Are we *sure* Ebola isn't airborne?

Since yesterday's post, several people have asked me on various social media outlets about the airborne nature of Ebola. Didn't I know about this paper ("Transmission of Ebola virus from pigs to non-human primates"), which clearly showed that Ebola could go airborne?

Indeed I do--I wrote about that paper two years ago, and it in no way changes my assertion that Ebola doesn't spread between people in an airborne manner.

Let me back up. The paper in question was an experimental study done in the wake of the 2008 finding of the Reston Ebola virus in pigs and a previous study looking at the Zaire virus in pigs. In the air transmission study, they inoculated pigs with Ebola and examined transmission to macaques (who were not in direct contact with the infected pigs). They did find aerosolized Ebola in air samples, and some of the macaques did come down with symptoms of Ebola. So, it looked like pigs could spread Ebola through the air, which is something that had already been suggested by the epidemiology of the 2008 pig Ebola outbreak. It's always nice when experimental data matches up with that observed during a real-life occurrence of the virus.

*However*, the kicker was not that Ebola is transmitted by air in human outbreaks, but rather that there may be something unique about pig physiology that allows them to generate more infectious aerosols as a general rule--so though aerosols aren't a transmission route between primates (including humans, as well as non-human primates used experimentally), pigs may be a bigger threat as far as aerosols. Thus, this may be important for transmission of swine influenza and other viruses as well as Ebola.

So unless you're sitting next to an Ebola-infected pig, seriously, airborne transmission of Ebola viruses isn't a big concern. (Perhaps this corollary should be added to this handy diagram examining your risk of Ebola).


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Pigs don't wear pants.

Read it as sufficient number of pigs, humans or other potential hosts infected and living in close quarters for the above comment. Such mutation events are more likely in industrial farms

By Able Lawrence (not verified) on 03 Aug 2014 #permalink

I would like to see some molecular epidemiology study of ebola virus

Considering the symptoms for a late-stage Ebola victim are heavy sweating, vomiting and diarrhea, I am not so sure that humans arent effective at creating aerosols at the height of infection.

Do we actually have data on the aersolization potential of humans at the height of infection, or are you assuming?

By mulletman99 (not verified) on 03 Aug 2014 #permalink

We have 40 years of epidemiological studies in humans and many experimental manipulations of various non-human primates.

If this ebola variant isn't airborne, how did more than 100 health workers outfitted with Biohazard suits contract the disease? It is pretty obvious, I think, that this ebola outbreak is spreading through the air.

By TJ Harvey (not verified) on 03 Aug 2014 #permalink

HCWs are special cases. One, they're in very close contact with a variety of body fluids. Two, they don't always have access to the protective suits you mention. This outbreak has dispersed so widely that especially when it hits a new area, most workers will not have such gear, and that's typically when it's most lethal for doctors/nurses/etc. If it were indeed spreading efficiently through the air, you would expect other close contacts who live in proximity to cases to become infected at high rates. We just have not seen this epidemiologically, and if it were efficiently airborne, honestly the number of cases would be much higher than it is right now.

Ebola is a very bad disease but why that doctor that treat this disease must cover there body mostly there face when this disease isn't airborne? Moreover can this disease be transmitted by hand shake or by sharp object like needle,blade etc.....|

By folorunso temitope (not verified) on 04 Aug 2014 #permalink

This is an excerpt from an update on the CDCs website. Correct me if I'm wrong but this sounds like the definition of a airborne virus (or bacterium) and the same words are used when describing airborne TB, influenza and others.

"Provide the sick person with a surgical mask (if the sick person can tolerate wearing one) to reduce the number of droplets expelled into the air by talking, sneezing, or coughing"…

TJ Harvey @#7 - I think it'll be most telling to ultimately hear from Dr. Kent Brantly as to how he thinks he was infected. Since Ebola hadn't been seen in west Africa since 1994, facilities were underprepared administratively for such an outbreak. Patient intake was reported as chaotic and not well-controlled. All you need is one infected person running in from outside and you getting vomited on (often at your nose and mouth) for you to be infected when the suit is off.

By David Kroll (not verified) on 04 Aug 2014 #permalink

Until the new virus is tested in human / primate scenarios, we will not know if this version of Ebola is spread via air. Any volunteers?

Drew, that is basic protocol for a lot of illnesses. Ebola also doesn't seem to be spread efficiently by fomites (inanimate objects such as doorknobs, countertops etc.) but using a mask like that will also minimize any fomite contamination and therefore exposure to others in numerous ways. Of course when transporting or caring for someone who is infected, they will always recommend an abundance of caution--understandably so.

"So unless you’re sitting next to an Ebola-infected pig"

So how does that not apply to half of africa? I have seen no mention of domestic animals being considered as disease vectors in current outbreak, even tho its known that most domestic animals can get infected with ebola and thus spread it.

By r2k-in-the-vortex (not verified) on 04 Aug 2014 #permalink

Is it "not airborne" in the same way that norovirus is not airborne? (i.e. - can be ingested in the aerosolized droplets of vomit/feces if you're standing near the person when they get sick?)

Because norovirus is not technically "airborne" like influenza, but you can still become infected by breathing in the airborne vomit/diarrhea droplets of an infected person. If that's the case for Ebola, this article is not wholly truthful.

By Reality Chick (not verified) on 04 Aug 2014 #permalink

#15 r2K, animals are usually considered as a possible source of an outbreak (eg an animal becomes infected by the bat reservoir, humans hunt/eat it, and become sick). It is theoretically possible domestic animals may also become infected by their ill owners but that doesn't really seem to be a factor once the outbreak is already underway.

Until someone in the know can make statements that do not contain "may be" (appears 3 times in the above 316 word blog) - I suggest assuming the worst and taking maximum precautions against infectious spread of ebola via all routes, including airborne..

By Lawrence Frieders (not verified) on 04 Aug 2014 #permalink

Reality chick, again, theoretically that is possible, but you have to consider the difference in infectious doses between the two viruses and their route of entry into the body. It only takes ~18 viral particles for Noro to cause an infection, and typically the issue with aerosolized vomit and other materials is that they can land all over and then be ingested (landing directly on food, landing on fomites where food will touch, contaminating hands, etc.) Very different picture with Ebola, where it needs to be directly inhaled.

Lawrence, absolutely--and they are. Dr. Brantly arrived and has been transported in a suit and so were others working with him (…). An abundance of caution is always used. However, my point is that for the average Joe, even if Dr. Brantly were ill and next to you on a bus/train etc. (as happened with Patrick Sawyer, the American who died in Nigeria), you're at extremely low risk of contracting the virus. Thus, all the panic about bringing Ebola victims into the U.S. as if that were going to set off an epidemic are extremely overblown, and particularly those who are using the research article cited above to do so.

I am shocked, LITERALLY shocked, that no one--not a single person on here including the author(op)--has read "The Hot Zone". It was proven back in 1983 and 1986 by nancy jaax and eugence johnson thst ebola zaire was airborne. These two people both worked in level 4 biolevel labs at USAMRID in maryland. In the book both commented and proclaimed how monkeys came down with ebola without direct contact (no, pigs weren't even mentioned in the book at this point. It would take a minute to text their work, but feel free to read it yourself. Theh have known for years of its airbornw capability.

I've read the Hot Zone more than once. Please don't get your science from the Hot Zone. It's a great book and very entertaining but...dramatized. Please note the lack of any citations or references in that book as well. Or, frustratingly, an index. Do you have a page # for that so I can comment?

I understand that. My concern is how they word it exactly the same way for TB, influenza and others. They keep mentioning "air" in new updates which is what bothers me. Also the NIH has a document about how it can be aerosolized.

Set aside I want to thank you and all other health professionals for what you do. It's truly an honor the battle you all fight. It's the unknown and the extremely rare possibility of a mutation that scares me.

I also fear that the disease is airbone, if not, then how come its spreading so fast? 700 cases is a huge & a very serious number

By pumla cele (not verified) on 04 Aug 2014 #permalink

So is evolution of the primate viral strain out of the question?

Pumia, it's actually more than 700 cases, but remember that is spread over (now 4) countries. There are more malaria cases than that every hour.

Drew, well, the news often gets things wrong. And sure, it *can* be aerosolized mechanically. That's a concern for bioterrorism--that someone would make Ebola in large quantities and somehow spread it via aerosols. Pretty much any pathogen can be aerosolized, but what I'm talking here is what actually happens during an outbreak, not theoretical manipulations of the virus. And multiple studies have shown that aerosol transmission just is not a factor in spreading this virus in human outbreaks.

Eric, I'm not sure what you mean by "primate viral strain."

I don't think this is correct. There are papers discussing human cases of Ebola and Marburg in which no direct contact with an infected person or animal can be shown. I will look for them as I've lost track of which ones they are.

Also, these are viruses we're talking about, which evolve faster than any known organisms. To some degree it doesn't matter whether or not there have been definite transmissions apart from direct contact, what matters is whether that potential exists, such as where different strains recombine in a carrier or host. That's exactly the concern with H5N1 flu and humans.

By Jim Bouldin (not verified) on 04 Aug 2014 #permalink

I´m no doctor like most of you but isnt the zaire strain (among others) quite likely to fail in its reproductions process? In other words, likely to mutate.

Isnt it just math. Eventually it will mutate and become airborne right? The most efficient strain at infecting new hosts will eventually be the prominent one.

So. If we dont already have more then one strain going its pretty likely that we will eventually, right?

We have never had such a large outbreak before, so the risk of getting a serious mutation is now larger then ever before and it will become theoretically larger for each new victim infected.

Then again, Im no doctor and I dont really know this stuff. But that was my theory anyhow. Please prove me wrong.

Best regards. Tobias

Jim, you are correct, there are. But that doesn't necessarily mean they are airborne--it just means there is a gap there and we can't definitively identify the source.

I'm well aware of the rapidity of viral evolution, but will point out again that this strain has been very stable over the 40 years that we've been observing it, despite it being an RNA virus. And again I'll ask if you think, then, that the same precautions should be taken with HIV? Also an RNA virus, also evolves rapidly, also transmitted by close contact with blood and body fluids. Do you expect it to become efficiently airborne any minute? If not, why not, and why the focus on Ebola in this manner?

Tobias, yes, it mutates. However, there is no inevitable path that the virus will take to become readily transmissible by air. Evolution is always a tradeoff between advantages to the virus and disadvantages experienced by the host, and whatever combination of factors that enables more efficient transmission to a new host will win over the long term. However, keep in mind that humans aren't really Ebola's host--bats are. We're incidental.

I am reading that the medical personnel in Africa wore BL3 suits and became infected. The returning Ebola-infected missionaries are now being handled with BL4 suits which have O2. Another interesting read:

"Why Aren’t Previously Successful Methods Used to Stop Ebola Working Against This New Strain?" (Pacific Standard) by Rebecca Buckwalter-Poza

By Charles Whitlatch (not verified) on 04 Aug 2014 #permalink

Tara - It is true that some of the HCWs may not have taken the appropriate precautions. But we're talking about more than a handful of HCWs. Some of the top ebola doctors have become infected and died, and we can only presume they were aware of the dangers and were taking every possible precaution. Moreover, if you read journal entries of some of the HCWs you will notice that extreme precautions were being taken (rubber boots, gloves, biohazrd suits, masks, etc.) and yet in those entries HCWs were still reported as contracting the disease.

If you graph the progression of ebola cases (and deaths), you will see that the disease has been spreading at an exponential rate, with a noticeable upturn in the "hockey stick" in early June. The non-linear nature of the incidence rate suggests we are dealing with a virus that is more akin to an airborne flu than a "fluids exchange" virus.

Looking at the numbers you will also see that the fatality rate is presently around 50%, which is historically a low rate for ebola. However, you will also see that despite a lower fatality rate, the virus is infecting and killing far more people than any other ebola outbreak in history. In my opinion, this seems to suggest that this variant has mutated and is achieving increased transmission combined with reduced host fatality, which is a hallmark of evolving pathogens.

So in short, I'm very concerned at this point, and think it very unwise to assume that airborne transmission is off the table.


By TJ Harvey (not verified) on 04 Aug 2014 #permalink

I looked at the set up they have to transporting the two infected persons to the US.

It's basically a gutted Gulfstream III with plastic tent in it. The pilots do not wear Racal suits.

The pilots are either craziest or bravest people in the world.

By King Ferdinand… (not verified) on 04 Aug 2014 #permalink

TJ, that chart does look concerning, but if you look at the doubling intervals going back to March 25th, I don't think it's necessarily showing exponential growth that would be evidence of easy airborne transmission.

Starting with 86 cases on 3/25, the doubling period to 170 cases was only about 16 days. If the infection were spreading at an exponential rate, then you'd expect to see subsequent doubling periods of roughly the same duration.

But the next doubling took about 50 days. The next two doubling periods after that have each taken about 30 days - with 1200 total infections being reported on July 23rd.

My read on that is that the infection started out spreading rapidly in one location (Guinea), but once it was recognized and a response was organized, the rate of new infections began to slow... until it spread into new areas, Sierra Leone and Liberia, where the process of organizing a response and educating the population had to start all over again.

So that's a plausible alternate explanation for why you might see a "knee" in a curve that isn't necessarily demonstrating exponential growth - we may be seeing an uptick in infection rates when the virus appears in a new area.

With more data, which unfortunately is a certainty at this point, the picture should become more clear.

By Paul Anderson (not verified) on 05 Aug 2014 #permalink

I am no scientist and I am no virologist, but I feel that the virus has either become airborne or has become MUCH easier to transmit. I am also horribly angry that the risk, no matter how small, has been taken to bring these people back into our country for treatment. I'm literally petrified to touch anything outside my home. I am going to go tomorrow and buy masks and gloves and hand sanitizer and bleach. My home is now a 'no one in' zone. All foods will be thoroughly cooked until nothing could have survived and water will be boiled and all items coming into my house will be cleaned with a bleach solution. Call me crazy, I don't give a damned, but I am protecting myself and everyone else should be too. Regardless if this woman says it mostly is not airborne. To me that means she doesn't have any more of a clue than I do.

"Eric, I’m not sure what you mean by “primate viral strain.”"

I mean the strain of the virus that has evolved to infect primates more specifically. I am assuming that there is not a single strain that infects all living hosts. The virus must evolve to different hosts at different rates depending on the virus life cycle, and this would lead to genetic differences that increase the infection rates of the virus within certain hosts. I am ignorant of the Eboli virus. My question is, more explicitly, why is the pig strain more easily transmitted? Is it due to a viral phenotype? Could the stain of the virus that infects primates more readily evolve to increase host-to-host infectivity?

Hi Tara,

Been reading your some of your papers on Staph aureus ST398, interesting reading…I'm a materials scientist not an epidemiologist thou. Been following the Ebola outbreak since March… With the numbers that we are seeing what do you think the possibilities of droplet transmission are?

I'm sorry Tara i just read your post of earlier today! Oops!

I know comparably nothing on the subject of VHF's and other viral pathogens compared to you but I agree with you about the possibility of increased transmission efficacy!

No, that was not by you but TJ Harvey…Coffee and wake up required…I'm not usually this dappy with my reading, honest!

Tara re. Nancy Jaax and transmission of Ebola zaire between monkeys with no direct contact, there was an article in the Lancet the abstract of which can be found here…
And another regarding the aerosolized transmission of ebola zaire in rhesus monkeys can be found here… (this is a full pdf version)

Rachel, if you live there you've already been an hour and a half away from Ebola, as it's been at the CDC since the 1970s. Nothing has changed so no need to panic. You may want to check out this post by Maryn McKenna, a reporter who covers infectious diseases and lives 2 miles away from Emory/CDC in Atlanta.

Chris, thanks--I've seen those before. Nice studies but still not what one would be exposed to during an outbreak situation unless, again, you're either a HCW or a family member of a victim--in which case odds are you'd have other exposures anyway.

TJ, to add to what Paul said, the epidemic curve alone doesn't show the route by which Ebola is transmitted. You can have the exact same curve for an infectious agent transmitted by air versus, say, oral-fecal. The curve will just tell you whether the outbreak is growing and if person-to-person transmission appears to be the reason why. We already know Ebola is transmitted person-to-person so the use of the curve is not as helpful in these situations (other than to monitor how bad it's getting in various areas in order to allocate resources).

Also, no one is taking airborne transmission "off the table." In every outbreak, a full work-up is done to figure out what can be done better, examine transmission, etc. That will surely be done in this case since it was so large and has so many complicating factors. If airborne transmission is shown to be a route of infection, that will be published and noted. But until that happens, inciting panic about airborne Ebola when years of studies and dozens of outbreaks have shown that type of transmission just isn't occurring in human outbreaks is irresponsible.

Eric, none have evolved "to affect primates more specifically." All are bat viruses which occasionally spill over into other animal populations (including primates).

Here's what I don't get. The argument is that the HCW who were infected just didn't take the right precautions or didn't have the right equipment available. However, some of these docs were leading Ebola experts. Not only did they know how to protect themselves, but they had (presumably) encountered the virus before, treated patients and never been infected. I'm assuming this of course, because I don't know how you become known as an Ebola expert without having treated Ebola patients. So what changed? Why did they become infected now? Something must be different in the virus to increase the infection rate and make the typical precautions ineffective in limiting exposure.

In response to Paul Anderson:

"Starting with 86 cases on 3/25, the doubling period to 170 cases was only about 16 days. If the infection were spreading at an exponential rate, then you’d expect to see subsequent doubling periods of roughly the same duration."

Except that there are reports speculating that family members are secretly burying their dead and failing to report some cases. As news of the outbreak spreads, there may actually be increasing numbers of unreported cases (due to fear, superstition, ignorance, political pressure, etc). Just because the rate of reported cases is not following a more aggressive track doesn't mean the reality matches the spin.

Tara, my heart goes out to you, having to deal with questions from all us laypeople, some of whom are pretty far out on the limb.

That said...;-)

What are the current best conclusions about:

1) Transmission via direct contact with a patient's sweat?
2) Transmission via contact with sweat recently deposited on fomites?
3) Transmission via any other bodily fluids recently deposited on fomites?

From those three points, we should be able to arrive at reasonable opinions about the risk of transmission under the conditions that people are worrying about in the US, such as if an Al Qaeda suicide terrorist got himself infected over there, came over here, and sought to spread it.

Re. HCW cases:

"In the field" precautions such as are being used in Africa, are less effective than the kinds of precautions we have at these special hospital facilities and in labs where dangerous bacteria and viruses are handled.

Per an interview on Public Radio, with a volunteer who had returned from Africa: Temperatures inside the field suits get up to 134 degrees, you're sweating rivers and it's getting in your eyes and causing serious discomfort, meanwhile you're trying to handle patients' IV lines and so on. The heat and dehydration alone make for compromised cognitive performance, increasing the chances of a fatal mistake.

OTOH, the systems in use at these hospitals include positive air pressure to the HCWs' suits, presumably air conditioned, and various measures to prevent dehydration and the like. If someone would publish a complete writeup about the safety precautions in use there, it would do much to reduce the anxiety and overt paranoia about this.

What I'm most baffled by is the fact that we even brought the cases here in the first place. My biggest question I'm left with is why didn't the doctors go to them? Is it because there were too many and that would be more difficult and dangerous? Because that seems rather preposterous.. They could've set up an isolation unit IN AFRICA but hey let's bring them here because there's "little odds of it spreading."

So Tara, you're absolutely positive that there is no possibility at all Eboila will not mutate to an airborne disease among humans?

I read this morning that four health care workers in Nigeria who attended to Patrick Sawyer have now contracted ebola. So are we to assume that there was an exchange of body fluids between Sawyer and four separate individuals? I really think it stretches credulity at this point to continue with the standard refrain that ebola cannot be transmitted through the air. At the very least, our health care experts should be warning the public that we simply not sure at this point.

By TJ Harvey (not verified) on 05 Aug 2014 #permalink

Common sense tells me that if an animal can spread Ebola thru the air to another animal, then humans can possibly become infected from that animal with ebola from the air, which can possibly mutate at that point to an airborne disease. Am I right or wrong?

Too many uncertainties to just assume it is safe. I don't know why we would risk spreading an outbreak here...just doesn't seem logical to me. Why couldn't they treat the patients there? Fly all the equipment there and treat them in the plane on the tarmac, but to bring it back to Atlanta?! If you have to bring them back they why not Alaska? Why Georgia where the climate is more comprable to what you would find in Africa?

Ebola is not something anyone wants to expierience, and I wouldn't take anyones word on this not being airbourne. The real answer current signs point to it not being so, but noone knows for sure.

And for anyone to have much faith in the CDC is a bit ludacris considering the recent smallpox viles found "lost" in some storage closet. I don't feel too cozy...

Tara - If you extrapolate the current epidemic curve, you find that by June 2015 every person in the world will have caught this disease. Now we all know that this is impossible, but my point is that we are looking at very significant rate of exponential increase. I'm not a microbiologist, but I have a hard time believing that a virus that can only be spread by an exchange of bodily fluids would move at such a rapid rate.

It is true that no one is taking airborne transmission "off the table." So I apologize for my loose choice of words. But there can be no doubt that at present the overwhelming message coming from the media and its "popular scientists" is that ebola is not an airborne disease, that this is a typical ebola virus, and that for most of the world there is not yet a real concern. I think these are very dangerous assumptions to make.

You state that "If airborne transmission is shown to be a route of infection, that will be published and noted." So let me ask you a few questions on that point:

> What is the objective standard for making the formal, worldwide determination that this ebola is airborne?

> Who gets to make that determination? The medical establishment? The CDC? The UN?

> How is that determination made? Unanimity between a certain group of bureaucrats? A proclamation from the President? A majority vote from a panel of international scientists?

> What is the time table for making that determination? Do we give a week for debate? A month?

My hunch is that neither you, nor any other person in government, academia, or medicine, has any idea how to answer these questions. And that is a big problem because when dealing with non-linear, complex systems that enter positive feedback loops, you don't have the time to figure these things out on the fly. You don't have the time to engage in a debate about the evidence. You don't have the time to engage the bureaucratic process. You don't have the time to weigh your options. By the time you recognize that a positive feedback loop is in place and is becoming a threat it is too late to do anything about it. This is especially the case with a disease like ebola, where there is a significant lag in the time that it takes for the disease to produce visible symptoms in its victims.

So in closing, what I am saying is this: You and other experts will be proven correct about ebola until you aren't. And when you aren't we could very well witness the greatest loss of life in the last 10,000 years of recorded human history. When dealing with non-liner systems, nothing is gained (in the long run) by trusting that standard assumptions (all based on a very short historical period) will hold true. Nothing is gained by assuming a best case scenario. Nothing is gained by allaying people's concerns for the sake of preventing a panic. To the contrary, when dealing with a virus that could potentially kill the majority of human beings on earth, we should be assuming the worst, and should be taking every precaution available ensure that the world is protected should standard assumptions fail.


By TJ Harvey (not verified) on 05 Aug 2014 #permalink

If we are so sure the virus isn't airborne, then how are so many ppl that were in contact with Patrick Sawyer now infected with the disease. We know once he collapsed they whisked him away to quarantine, they knew where he originated from. I doubt very seriously people in the airport where rushing over and getting in contact with his bodily fluids. They are terrified over there.

Don't get me wrong I'm not panicking nor do I believe this will turn into a worldwide pandemic. Anything of course is possible, but I choose not to freak out just yet. I am very curious though, we all know the government will not tell us right away if it is airborne or any real threat to the US. We are on a need to know basis as far as the government is concern. I understand in part, not wanting to panic an entire country.

TJ, instead of looking at the infection growth as a single curve, I think it makes more sense to look at the curves for each country where there has been an outbreak.

Each country has its own public health system and its own challenges in term of educating the population in how to avoid becoming infected, and each one started dealing with the problem at different times.

When you look at the data that way, the growth in Guinea looks linear, and the later outbreaks in Liberia and Sierra Leone, which are still in the early rapid growth phase are expanding more rapidly than the original Guinea outbreak, but also in a linear fashion.

I think it's the combination of those numbers into a single chart that creates the impression of an exponential curve.

Take a look at the charts at this link to see what I mean:…

By Paul Anderson (not verified) on 05 Aug 2014 #permalink

Scott, I haven't seen a good report on the level of experience some of these docs have. They're characterized as "leading doctors" etc. but they were in & from Sierra Leone & LIberia, countries which had never seen Ebola before. I don't know (and haven't seen) info on whether they worked in outbreaks previously in DRC or Uganda etc., but it's possible they were "leading experts" just because of this epidemic and had no experience previously treating Ebola. Just take some of those characterizations with a grain of salt for now.

G, yes, exactly re: suits etc. Re these:

"What are the current best conclusions about:

1) Transmission via direct contact with a patient’s sweat?
2) Transmission via contact with sweat recently deposited on fomites?
3) Transmission via any other bodily fluids recently deposited on fomites?"

1) risky. 2 & 3) uncertain. Fomites probably do play a role (bed linens, virus on protective gear/suits etc.) but it's tough to quantitate how much during an outbreak like this.

Re Nigeria, I've seen only 2 cases confirmed.… from 4 hours ago. Excerpt: "Idris noted that the occurrences of secondary cases disease was expected giving the nature of contacts these persons had with the patient from Liberia adding that this was because they were unaware of his status until the management of the hospital reported their suspicions to the State government."

Realist--"So Tara, you’re absolutely positive that there is no possibility at all Eboila will not mutate to an airborne disease among humans?"

I've never said that. I've pointed out the analogy to HIV. Why aren't people worked up about that "mutating to an airborne disease among humans"? Because it's biologically implausible. Not impossible, but unlikely. Same for Ebola. Some small amount of aerosolized transmission (usually mechanically) is not the same as saying Ebola is an airborne disease.

TJ, science works by reporting, evaluating, and re-evaluating facts and observations. There are already a number of publications on the West African outbreak. In 1999 there was an entire issue of the Journal of Infectious Diseases devoted to Ebola. It has nothing to do with a presidential proclamation and everything to do with weight of scientific evidence.

Scott, I agree that the reported numbers very likely understate the actual size of each outbreak.

But it's not the magnitude of the numbers that's of as much concern as the rate of change. In other words, let's say for the sake of discussion that 80% of infections are not reported.

If those infections were reported, that would change the scale of these curves, but it wouldn't necessarily change their slope.

If there's some reason to believe that the rate of reporting is dropping as time goes by and more effort is put in to tracking cases and educating the public, then that would be a reason to question the rate of change in the infection curves, but thus far I haven't heard of any reason why the reporting rate would trend in that direction.

By Paul Anderson (not verified) on 05 Aug 2014 #permalink

The pig study is meaningless . The evidence to look at are the more than 100 medical staff and doctors who have contracted ebola while treating patients.
I could even ponder that the staff were at fault for mishandling urine and other bodily fluids. But not the doctors . They would not touch any of them without gloves.
This indicates that the ebola virus has mutated and now is airborne.

By Dr Warzburb D (not verified) on 05 Aug 2014 #permalink

I am not a physician or scientist, but I think that most people here are making some serious errors in deduction. If the virus had become truly "airborne", meaning that it could spread in a similar fashion to influenza or the common cold, we would be seeing a dramatically higher rate of infection. For example, of all the people who came into contact with Patrick Sawyer while he was symptomatic, the first person to contract the disease was his doctor. None of the passengers who share the flights with him have been diagnosed positive.
You can argue semantics, but I think Tara has acknowledged the possibility that the HCWs could have been subjected to aerosolized (not airborne) infected fluids from their patients. This is much more likely than a true airborne mutation.
And yet another point which which I agree, is that we seem too ready to believe that this disease has become airborne, when so many other blood-borne viruses, like HIV, have not.
Is it scary? Hell yes! But I think the panic is going to hurt more people in this country than the Ebola outbreak ever will.

Re the comments in "Hot Zone" and airborne transmission-
It's been years since I read it, but I reread the section where Nancy Jaax relates that she believes EBOV spread via air from monkeys injected with the Reston strain to uninjected ones. In her quoted statement, she notes that monkeys "throw poop", literally, in such settings.

She showed, that when forced to inhale EBOV directly, that primates can be infected (Johnson, E., Jaax, N., White, J. & Jahrling, P. Lethal experimental infections of
rhesus monkeys by aerosolized Ebola virus. Int. J. Exp. Pathol. 76, 227–236 (1995).)

A more precise way to summarize the evidence is that while experimental airborne transmission to primates via an airborne route is possible only under very constrained conditions, the human epidemiology shows that practically, it isn't transmitted between humans by air. Absence of proof isn't proof of abscence, but well designed, controlled experiments in primates show "that airborne transmission of EBOV between NHPs does not occur readily, and ... suggests that the route of exposure may impact shedding and the subsequent opportunity for transmission"

Evaluation of transmission risks
associated with in vivo replication of
several high containment pathogens in a
biosafety level 4 laboratory
Judie Alimonti1*, Anders Leung1*, Shane Jones1, Jason Gren2, Xiangguo Qiu1, Lisa Fernando1,
Brittany Balcewich3, Gary Wong1,4, Ute Stro¨her1{, Allen Grolla1, James Strong1,4,6 & Gary Kobinger1,4,5,7

I totally get why people are concerned about airborne transmission, but it seems like it really isn't a thing.

I've yet to see any study that shows person to person airborne transmission. In lab settings, we've got pig to monkey, and monkey to monkey. This suggests that Ebola is reproducing at higher rates in different tissues in different species, and/or there is something about they way those non human animals are producing aerosols that is different.

There are, at the same time, a couple of studies that looked for airborne transmission in humans and ruled it out, along with the general observations of people in the field.

Abstract: The surviving members of 27 households in which someone had been infected with Ebola virus were interviewed in order to define the modes of transmission of Ebola hemorrhagic fever (EHF). Of 173 household contacts of the primary cases, 28 (16%) developed EHF. All secondary cases had direct physical contact with the ill person (rate ratio [RR], undefined; P < .001), and among those with direct contact, exposure to body fluids conferred additional risk (RR, 3.6; 95% confidence interval [CI], 1.9–6.8). After adjusting for direct contact and exposure to body fluids, adult family members, those who touched the cadaver, and those who were exposed during the late hospital phase were at additional risk. None of the 78 household members who had no physical contact with the case during the clinical illness were infected (upper 95% CI, 4%). EHF is transmitted principally by direct physical contact with an ill person or their body fluids during the later stages of illness.
Between 31 July and 6 October 1979, 34 cases of Ebola virus disease (22 of which were fatal) occurred among five families in a rural district of southern Sudan; the disease was introduced into four of the families from a local hospital. Chains of secondary spread within the family units, accounting for 29 cases resulted from direct physical contact with an infected person. Among all persons with such contact in the family setting, those who provided nursing care had a 5.1-fold increased risk of infection, emphasizing the importance of intimate contact in the spread of this disease. The absence of illness among persons who were exposed to cases in confined spaces, but without physical contact, confirmed previous impressions that there is no risk of airborne transmission. While the ecology of Ebola virus is unknown, the presence of anti-Ebola antibodies in the sera of 18% of persons who were unassociated with the outbreak suggests that the region is an endemic focus of Ebola virus activity.

Airbonre transmission in Ebola does not seem to happen at this time. There is no reason to think it would emerge as a characteristic of this disease, but there is also no reason to rule it out for the future. But there is also no way to assess the probability of that happening other than to say that it seems very unlikely with this kind of pathogen.

Now, put on your tin hats for a moment. Various military research units around the world have, it seems, looked a Ebola very closely. On one hand one might want to make a nice airborne version of it but, officially and (hopefully) more likely, one might want to assess the efficacy or possibility of that, in order to respond if the bad guys (whoever they may be) do so. As far as I am aware this led to nothing for Ebola. If Ebola could be made to be airborne, one might expect that there would be a USAMRIID response to that.

Also worth mentioning since the comparison is made here and there.. Influenza reproduces in such a way that the chance of a major genetic change in the virus is potentially very high. Ebola does not, I'm pretty sure.

Ok so the consensus I'm getting all over everything about Ebola is they are mistaking droplets being expelled by coughing and sneezing as being defined as airborne. From what I can tell that is not the scientific definition or a airborne classification. That's also where I got confused. I think people need to understand the difference between the two because it confused me along with almost everyone I seen about it. Education and not fear mongering should be our goal. Another ignorant response I see from people is why do they suit up in full gear when "it's transmitted the same as hiv". Being ex military who responded to CBRNe incidents we always dressed up to respond at the highest level until we can prove and justify lowering ppe. My conclusion is I think the lack of factual education is the number one problem in the US while the main problem in Africa is the lack of human resources and medical supplies/facilities. Since my first post I have changed my perspective about Ebola. Dangerous yes but awareness and proper ppe and proper decon procedures must be strictly followed as one mistake could lead to infection. Also I want to add that most people seem to think that the 2-21 incubation period means that people can be contagious without knowing it. According to cdc and WHO you must be experiencing symptoms to be contagious. Correct me if I'm wrong but that's where I'm sitting on the situation now compared to the earlier "i don't understand definitions but it sounds like they are saying it's airborne". Also reading that 2012 study the hot zone is seemed very flawed as a experiment.

I think I know where this problem is coming from:

People are confusing "aerosol" with "airborne." Aero as in aeroplane, and since aeroplanes are airborne, QED (mistake).

Therefore the following descriptions (I'm doing this from memory):

Aerosol: Sprayed into the air but NOT carried by air currents. Droplets, usually macroscopic, that can be sprayed into the air but rapidly fall out of the air onto surfaces. Think of someone spitting by going "pppppptooie!" and large and small droplets of spit landing on whatever is nearby. You don't generally inhale aerosols, but if the droplets land on your skin and get into an unprotected cut or scrape, or if you get them on your hand and touch your face, the infectious material can get to you that way.

Airborne: Sprayed into the air AND carried by air currents. Very tiny droplets, usually microscopic, that remain floating in the air and can be carried by air currents. Think of a cough or sneeze: you usually don't see the droplets spewing into the air but there they are, and there they remain, floating around to be picked up by anyone who is breathing nearby. Airborne particles aren't usually picked up through cuts and the like, but are usually picked up by breathing the air in which the particles are floating.

Is this useful?

Hi, thank you for your time. What about the following comments that this version of Ebola is not actually the Zaire strain?

"This particular strain of Ebola is not Ebola Zaire. This is a new strain, and it may in fact be more dangerous than the Zaire variety. Not because of any difference in the symptoms (the symptoms are identical), but because this new virus seems to be harder to contain. Whether this is due to some characteristic of the virus itself or merely dumb luck is uncertain at this time, but the rate at which this outbreak has extended its range is unprecedented.

According to the CDC this virus is genetically 97% similar to the Zaire strain. However if you are interested in this virus’ phylogenetic relationship (genetic lineage) to the Zaire strain you should look read “Phylogenetic Analysis of Guinea 2014 EBOV Ebolavirus Outbreak” on

Another study by the New England Journal of medicine (this was the one referenced by the CDC) specifically names the parts of the genetic code which differ:

The three sequences, each 18,959 nucleotides in length, were identical with the exception of a few polymorphisms at positions 2124 (G→A, synonymous), 2185 (A→G, NP552 glycine→glutamic acid), 2931 (A→G, synonymous), 4340 (C→T, synonymous), 6909 (A→T, sGP291 arginine→tryptophan), and 9923 (T→C, synonymous).

Note that there doesn’t yet seem to be a consensus as to what this new strain is called. One study referred to it as “Guinean EBOV”, another as “Guinea 2014 EBOV Ebolavirus” and others are still referring to it as Zaire. Given that we can specifically name the points where the virus has mutated, using the old name is misleading. "

Source, which has further links to other sources:

Unfortunately, some comments are being censored by the moderator.

However, regarding the aerosol issue - here are the definitions from the CDC:

The following definitions are used in
the list of diseases and guidelines
developed pursuant to Section 2695[42
U.S.C. 300ff–131]:
Aerosol means tiny particles or
droplets suspended in air. These range
in diameter from about 0.001 to 100 μm
(Baron P, accessed 2010) (Baron PA and
Willeke K, 2001; 1065).
Aerosolized transmission means
person-to-person transmission of an
infectious agent through the air by an
aerosol. See ‘‘aerosolized airborne
transmission’’ and ‘‘aerosolized droplet
Aerosolized airborne transmission
means person-to-person transmission of
an infectious agent by an aerosol of
small particles able to remain airborne
for long periods of time. These are able
to transmit diseases on air currents over
long distances, to cause prolonged
airspace contamination, and to be
inhaled into the trachea and lung (Baron
P, accessed 2010) (Seigel et al., 2007;
Aerosolized droplet transmission
means person-to-person transmission of
an infectious agent by large particles
only able to remain airborne for short
periods of time. These generally
transmit diseases through the air over
short distances (approximately 6 feet),
do not cause prolonged airspace
contamination, and are too large to be
inhaled into the trachea and lung (Baron
P, accessed 2010) (Seigel et al., 2007;
Contact or body fluid transmission
means person-to-person transmission of
an infectious agent through direct or
indirect contact with an infected
person’s blood or other body fluids
(Seigel et al., 2007; 15).
Exposed means to be in circumstances
in which there is recognized risk for
transmission of an infectious agent from
a human source to an ERE (Seigel et al.,
2007; 14).
Potentially life-threatening infectious
disease means an infectious disease to
which EREs may be exposed and that
has reasonable potential to cause death
or fetal mortality in either healthy EREs
or EREs who are able to work but take
medications or are living with
conditions that might impair host
defense mechanisms.

what I would like to see more of is how we CAN catch the disease?..for example..yes by direct contact with bodily sweat on a persons hand? that during the incubation stage..(is that 3 weeks from initial contact?)..or does the contact have to be in the later stages?..I am planning to go to Kenya soon to meet someone flying there ALSO from LIBERIA...He has had a medical and blood examination to clear him for leaving the country... but that was a week before he plans to leave!!!...when I meet this person should I avoid physical contact with him of any kind??

By denise jones (not verified) on 06 Aug 2014 #permalink

Denise - From what we know historically, a person is not contagious until the symptoms are present. At that point, all bodily fluids, including sweat, can carry the virus.
A lot has been said about this strain being harder to contain, which has led to speculation that something has fundamentally changed with the virus. People are claiming that it has to have become airborne, or may now be contagious during the incubation period. In reality, it is the same cultural and sociological factors that are contributing to the ongoing outbreak, compounded by the fact that it appeared in a region that was not used to handling Ebola outbreaks.
As long as the person you are meeting is not sick, you should be OK.

Wasn't there also a case in the 80s with monkeys? The monkeys spread it to each other through the air ventilation system. So it can happen with 2 different types of animals but never humans?

I think you're being too dismissive of the *possibility* of airborne transmission. There are some paper in the literature suggesting that it's possible. For instance, a study back in the 90s that found transmission among monkeys without direct contact.

The best way to state this is that airborne transmission is not likely. Not that it doesn't happen.

I think you're being too dismissive of the *possibility* of airborne transmission. There are some papers in the scientific literature suggesting that it's possible. For instance, a study back in the 90s found transmission among monkeys without direct contact.

The best way to state this is that airborne transmission is not likely. Not that it doesn't happen.

Andrew, 97% still makes it Zaire per naming conventions. That's pretty damn closely related.

Questions and concerns:
So, because Ebola symptoms appear to be just like influenza in the begining but Ebola has high fatality rates, and requires the medical staff who treat your symptoms to test something that presents the same way as the flu...more than likely, the medical staff will send you home with scripts for nothing and wont take it seriously, nevermind how dangerous it is or easily communicable to others who are lax about sanitation and protection..Just walk into any ER these days....unless you are bleeding profusely from an known accident, they dont wear masks, the dont wear gowns, it is all "business as usual".. Why would they test vomiting and diarrhea and dehydration symptoms as anything other than common ailments, with a special Ebola test that they are unfamiliar with? They WONT until it is TOO late and many others are exposed.

i still struggle to understand how intelligent american health workers who know EXACTLY how to avoid contamination, know EXACTLY how to use safe hygiene, wearing max security hazmat suits or whatever, still caught the virus if it's not airborne. i refuse to believe either of them directly touched an ebola patient without protection.

if the ebola patient coughs on his hand and then turns a door knob, can i catch it by touching the same door later? that's just as bad as airborne to me. elevator buttons, bathroom door handles, stair rails, hand shakes... we are an unsanitary society. this virus will spread like wildfire if it gets out and can be transmitted this way.

not just cough on hand. i meant anything.. wipe sweat from forehead, suck their thumbs, etc.

My two cents on the "how can the HCW get infected if they were wearing PPE" issue - We dont know just how closely they are following their protocols, and they are putting themselves at risk every time they come in to contact with these patients. Ebola is so infectious that it only takes a tiny glove tear, improperly sterlized equipment, or other small mistake, to become infected. In a high stress environment such as that, human error is highly probable and even the "experts" are at risk.

By Jen PharmD (not verified) on 06 Aug 2014 #permalink

Amber, the 80's case with the monkeys was the Reston strain, which does not cause disease in humans. Very different virus.

Paul, I'm addressing human to human transmission in the context of this outbreak. Note I said right in the opening story that it's "not a concern." Not that it never can happen, but that it's rare enough that it's never been documented in humans to date, that experimentally it's rare even in animal models--hence, not a concern.

Andrew, they are doing this already. There have been reports from all over the country of possible patients being tested, including one in my neck of the woods in Ohio. It's more likely they're going overkill on this than missing cases with obvious symptoms.

"me" #82, except that they're *not* using "max security hazmat suits" or anything of the like in most of the hospitals/clinics. They're using suits but they're really just to keep off most of the fluids. Sometimes these are even washed/reused. It's very basic protection and sometimes it's not enough. Plus I noted earlier the issues with how hot the suits are, they can be claustrophobic, doctors and nurses are tired/overworked, etc. It doesn't take much of a lapse to expose one's self, unfortunately.

I appreciate your cogent explanations, but wish you'd stop using HIV as a counter-example. HIV when first identified was the subject of the same hysterical fear-mongering that we're now getting about Ebola from certain quarters - the American obsessions with doorknobs, toilet seats, and skin color were on full display. But HIV is actually far harder to spread. A news story has claimed that after the index case for one local outbreak took a long bus ride to the city where she was hospitalized, four or five of her fellow passengers came down with Ebola. That suggests not airborne transmission (otherwise there'd be a million cases, just like in flu epidemics), but pretty darn effective aerosol transmission. If you're in a vehicle with a guy with AIDS and he happens to have a stomach bug and vomits near you, you simply aren't going to catch HIV. I agree that the precautions they're taking at Emory are quite adequate, but the cheery statement one physician offered a while back that you'd be safe sitting on the bus next to a sick person doesn't seem to be true, at least in this outbreak.

Tara, thank you for your efforts and patience here. You are a hero for dealing with general scientific illiteracy and a freakin martyr for attempting to deal with conspiracy theorists. This has been a very informative article and Q&A. Thanks again!

Jane, yes, and in Africa Ebola is carrying the same or worse stigma because of all the misinformation. I've not seen that news story but I'd caution against some of those--there is, again, a lot of inaccurate information that is out there in the early days, and after actual scientific study, ends up getting rescinded. I'm also talking about the *evolution* of HIV--it's currently a blood-borne pathogen like Ebola, so why aren't people freaking out about its potential to become airborne? It is a more mutable RNA virus than Ebola is, which is my point on that comparison.


It takes 18 particles to infect with the norovirus.... How many particles does it take to infect with Ebola?

By Jerry Linebaugh (not verified) on 06 Aug 2014 #permalink


Sorry left some details out let me rephrase the questions.

1) It takes only 18 particles to infect with a Norovirus GII.4. Genotype so how many particles does it take to infect with the Zaire strain of Ebola or do we know?

2) what are the particulates exactly?

3) and thank you for shedding some much needed light as to the mechanical heavy aerosols humans make but more talk is needed. There are only a few studies I have found on human sneeze on aresolization but the best one suggested that some of the particulates (saliva droplet) could be airborn for hours. Explain the relationship to the up to 40,000 droplets especially the smaller ones that come rushing out nearly 100 MPH and how these particles suspended potentially for hours are not infectious?

Thanks again for your commitment to the science, the truth.

Jerry L

By Jerry Linebaugh (not verified) on 06 Aug 2014 #permalink

Tara, never mind HIV; why aren't we freaking out about airborne rabies or airborne HPV (hardly deadly, but an American peur du jour just the same)? Because there's been no indication that these viruses can ever be dispersed into the air, enter an intact human body, and cause infection. Same for HIV. I, not a virologist, would have assumed that just like some plants wouldn't survive in the desert no matter how much selective pressure to do so they might experience, some viruses just won't ever go airborne. But even if you assume there's no such thing as a virus that couldn't somehow become transmissible by respiration and tough enough to survive on surfaces, if a given virus isn't even aerosol-spread, it's a long, long way from being airborne.

I don't know that "scientific study" is either needed or possible in the case I asked about, unless by that you mean "waiting to hear results of final diagnostic tests, should those ever be publicized". It's either true or false that five bus passengers near this woman fell sick. If it's true, that's reason enough for people in the region to be uncomfortable sitting for long next to someone who looks acutely ill. The stigmatization of people who have had Ebola and recovered is a real shame, but where avoidance of sick people is concerned, you can't expect people to be comfortable possibly exposing themselves to a disease with a 55% to 60% mortality rate just because official experts have not yet definitively confirmed that they'd be in danger.

I just read that there are now eight health care workers in Nigeria who came into contact with Patrick Sawyer and died from ebola. This seems to suggest that this variant of ebola is highly transmissible, whether it be by air or even very slight contact with a victim's fluids.

Honestly, at this point the difference between airborne transmission and highly contagious droplet transmission is largely semantic. If this ebola virus is so contagious that it can be contracted by very slight contact with a droplet (e.g., touching a contaminated door handle, pen, or credit card) - which seems to be the case - then we are dealing with a very serious worldwide threat, and serious countermeasures need to be taken now.

By TJ Harvey (not verified) on 06 Aug 2014 #permalink

TJ - I read that Patrick Sawyer urinated on his nurses when they told him he had tested positive for Ebola. If true, it seems the most likely reason they got infected, not from exposure to single droplets of fluids. Sensational stuff, but no more so than all of the uncertainties and half-truths that are being reported out of Africa.
Whether the urination story is true or not, it seems likely that Mr. Sawyer was in denial about the cause of his symptoms, and had dangerous contact with others while symptomatic.

I'll note for TJ and Jane that the WHO still, as of today, doesn't list any confirmed cases in Nigeria--so most of those which are being reported are still awaiting laboratory confirmation. Again, with cases like these, the news gets ahead of the science which is where a lot of misinformation comes from.

Jane - There are two or three rabies deaths per year in the United States. If we suddenly experienced 20 or 30 rabies deaths in a three month period would you be concerned? Would you be even more concerned if some of the victims hadn't been bitten by rabid animals, and had simply been in the same vicinity of other victims? Would you register alarm if there seemed no end in sight to the rapid increase in rabies deaths and we were on track for 10,000 deaths per year?

What we are witnessing in Western Africa is unprecedented in the history of the disease (by many multiples). To not recognize the reality that something has changed seems more motivated by wishful thinking than actual logic or reason.

The media, medical establishment, and governments, are uniformly repeating the refrain that this is typical ebola and that there is nothing to fear if you live outside Western Africa. But the message is so consistent, so (dare I say) nonchalant, and so seemingly contrary to the facts on the ground that many people are doubting the veracity of the message and are left suspecting the worst. A more balanced message - one that recognizes that something is very different with this particular outbreak - would do a much better job allaying people's fears and helping the world properly prepare for what might be coming our way.


By TJ Harvey (not verified) on 06 Aug 2014 #permalink

I'm with TJ. The facts don't add up. This virus is spreading too quickly and infecting too many medical professionals. Last time I checked a person with HIV or rabies didn't infect their doctor and everyone that saw them when they went to the doctors office. Aerosolized transmission is likely IMO. Only a matter of time before it evolves to full airborne. The world needs to quarantine west Africa immediately, though it might be too late.

TJ, what you are minimizing is the behavioral aspects. Yes, unprecedented--but we simply cannot jump to the conclusion that it's because somehow, the virus has changed. Much more likely (& based on historical precedent) that large outbreak is due to fact that it's multi-national, in places that have never seen Ebola before (and thus are untrained & inexperienced), in countries with weak governments & infrastructures because of years of civil wars and instability.

Scared, actually, people with HIV have and do infect medical workers. The difference is that now we have protocols in place if workers get exposed (eg needlesticks) and we have drugs to treat/control HIV infection. We don't have that for Ebola.

I'm still not buying it. The comparison to HIV infecting workers isn't comparable - you're telling me a person with HIV can get off an airplane and infect 8 people they came into contact with that cared for them? Not happening. The story about him urinating on the nurses and that's how they got infected is ludicrous.

As far as poor facilities/training being to blame, the previous high for outbreak in Uganda (I think) was 430 cases or Uganda a shining beacon of healthcare and safety protocols and that's why the otubreak was limited? I don't think so.

Hi Tara,

Thanks for this post. You've done a great job addressing the issue and answering questions and comments. The more one looks at the popular media frenzy now occurring, the more one appreciates a sane response like this.

Regarding comments 32 and 34, I do agree that, AFAIK, there are no confirmed cases of aerosolized transmission. And even if there were a few such, this transmission mode would pale by comparison to direct contact with the symptomatic and/or their body fluids. This is very fortunate and it's definitely very important that people realize this, so as to avoid elevating the panic level even more than it already is. My point is simply that we cannot fully rule out this mode of transmission (which I think you agree with), even in the present, and definitely in the future.

I need to read that Science Reports article you reference, which I'd not seen before, to see what it says about the difference between pigs and humans w.r.t. clinical pathology and transmission mode, because that's a big concern, obviously, w.r.t. the possibility of genetic recombination of strains of potentially different transmission modes. Regardless, I think it's important to remember that the Filoviridae are still negative sense RNA viruses, and hence require RNA-dependent DNA polymerases, which have high copy error rates compared to DNA-dependent polymerases. This does not promote stability.

Here are a few references that discuss the possibility of airborne transmission. None are definitive, they just discuss the possibility. There are more, including some for Marburg, but I ran out of time tracking them down.

1. Gatherer, 2014, (in press). The 2014 Ebola virus disease outbreak in west Africa, lines 185-198

2. WHO RISK ASSESSMENT, Human infections with Zaïre Ebolavirus in West Africa, 24 June 2014.
pg 4, "Evidence of human-to-human transmission"…

3. Roels etal 1999. Ebola hemorrhagic fever, Kikwit, Democratic Republic of the Congo, 1995: risk factors for patients without a reported exposure

4. Bausch etal 2007. Assessment of the Risk of Ebola Virus Transmission from Bodily Fluids and Fomites
First paragraph of discussion section regarding live virus in saliva.

5. Dowell etal 1999. Transmission of Ebola Hemorrhagic Fever, A Study of Risk Factors in Family Members, Kikwit, Democratic Republic of the Congo, 1995
Table 2: "Exposures during late illness: Conversation"

By Jim Bouldin (not verified) on 07 Aug 2014 #permalink

Scared - The reason I brought up the urination story (and I agree, it is pretty ludicrous) was to highlight the fact that simply reading the stories published about this outbreak is not enough to really develop an informed and rational opinion. Added to this is the fact that Ebola is a virus that triggers a primal fear response in many people.
I think Tara has done a great job commenting on the specific, historical data that help explain how this outbreak grew to where it is now. Your reference to the previous high death total for an outbreak is actually relevant. The very first outbreak in Zaire (DR Congo) in 1976 killed 280 people. That was the first time it had ever been experienced in that country. Now it is in three countries (maybe four) where it has ALSO appeared for the very first time. That alone is enough to magnify all of the things that make an Ebola outbreak dangerous. There are no space suits, healthcare workers are overheated and overworked, and the locals are scared to death and threatening violence against the doctors trying to control the epidemic. It is already a perfect storm of awfulness, without the additional panic that somehow the virus has mutated and now we are all at risk.

Tara, let me thank you for your dedication to enlighten us and assuage our fears. I also want to thank the CDC for bringing our citizens back home to be treated. I too have read the Hot Zone ages ago, which is why I know it was the right coarse of action and the safest place to treat them as effectively as possible. Like others though, I am concerned about this outbreak. I do not believe that this particular strain of the virus has gone airborne. If it had gone airborne, then the infection rate would be exponentially higher than what it is now. I do not however, rule out short travel through the air by means you have already covered.
Notice how so many keep saying, something about it has changed for it to infect so many. They are correct. Ebola Zaire had a high (90% or so) mortality rate and a very short incubation period (24-48hrs if remember correctly) which is why it basically "burned itself out" once the world's health organizations stepped in. This slightly mutated version has a significantly lower mortality rate and a much longer incubation period which helps a pathogen spread more easily. One of the first symptoms people tend to miss when they become infected with almost anything, is a low grade fever. They tend to write it off to being hotter out or they're working harder than normal and think nothing more of it until other symptoms hit and they have a noticeable fever. But if this pathogen is like most, then even with a low grade fever with no other symptoms yet, they could be contagious if someone were exposed to their bodily fluids. So I think it is quite possible, it is being spread in the earlier stages before people realize what they are dealing with and seek medical treatment. Close family members are more likely to become infected. After putting their very ill relative in the hospital, they probably went to stay with extended family members or close friends that lived nearby not realizing that by this time, they themselves were infected, thereby giving the pathogen new hosts to infect and spread from.
From my understanding of infectious diseases, the lower the mortality rate and given a decent incubation period, the more likely it is to become widespread (not as widespread if it were airborne) before it became noticed. So, to me, it's not surprising that this slightly mutated version has infected so many. I'm just thankful that it's spread has been so slow as maybe this will give the CDC, NIH, and/or WHO the time to come up with something to effectively combat it before it takes too many more lives.

there may be something unique about pig physiology that allows them to generate more infectious aerosols as a general rule

I've worked with pigs as lab and farm animals. Pigs snuffle, snort and produce amazing quantities of snot (nasal mucus) even when they are healthy ... it's an adaptation to keep their nostrils clear of dirt when they are rooting for food. One big snort blows the dirt out, stuck in a glob of mucus.

By Tsu Dho Nimh (not verified) on 07 Aug 2014 #permalink

Thanks for this. It's nice reading a professional opinion on the matter with some clarity about the pig/monkey report. I know many people who are freaking out about this. We hear the weird outbreak and think the world is ending. It is a very serious outbreak, but there are many factors that have made this outbreak worse, including lack of proper supplies, lack of doctors, and many people afraid of taking loved ones to the hospital (they don't trust them from past experiences, and they believe ebola to be fatal anyway, so they don't see the point in going).

As said before by others, I take my hat off in admiration for the health workers who selflessly and relentless strive to care for those currently affected by ebola… After seeing the WHO press conference regarding their declaration of International Emergency and the unavailability of experimental agents due to them being untested and in extremely short supply, I find this explanation a little weak. As if health care professionals didn't have a hard enough time over streched and battling 40 C heat in protective suits, they have no drugs to offer both to the citizens or to each other.

I just read a paper on an incredibly simple molecule which would be both cheap, easy to produce (in a reactor not a monkey) and has also been through phase I, II and III trials for Influenza viruses, H5N1 and others, which has shown at least some efficacy in small animal models. The drug, Favipiravir, showed suppression of replication of Zaire EBV (Mayinga 1976 strain) in cell cultures by 4 log Units and in type 1 interferon receptor lacking mice when administered 6 days post infection (2-4 days before death in control animals) prevented lethal outcome in 100% of mice. With the safety assessed in phase I trials already established and it's simplicity and low cost to make I wonder why this is not on the table to establish its efficacy in health workers and patients at this current juncture in the proceedings?

yes. I have a post on that ready to go but was waiting on a comment from the senior author. I'm guessing that probably won't be forthcoming though...

Tara, I think it's awesome you posted this AND also follow up, patiently answering concerns. Thank you for doing this and for the education.

Question(s): Can the virus (or any virus) be spread by both bodily fluids AND be airborne or aesolized? Can they have multiple modes of transmissions? Can mosquitoes be spreading this current form of Ebola?

I have read every single comment and your answers Tara. Thank you so much for giving straight answers to difficult questions in such a way that I now have more insight into this disease than any news article, WHO or the CDC have given us up to now. And thanks to others who have posted on here who actually KNOW what they are talking about.

By Sue James (not verified) on 08 Aug 2014 #permalink

Dr, Smith, thank you so much for the great information!

And PEOPLE, PEOPLE...calm down. Like I told my dad twenty years ago, if AIDS was as easy to get as the common cold, it would spread just as quickly as the common cold.

I'd still love to know why ZMapp and TMK Ebola, both I think yet to complete Phase I trials, and therefore without any proven safety, when Favipiravir has phase 2 completed and showed such promising results with EVD. It's cheap and simple to make, I mean damn, its got a molecular weight of 157.1, Ibuprofen's is 206. Any comment Tara?

There was some question about the number of confirmed cases in Nigeria. The CDC is reporting on August 9th that Nigeria has 13 suspected cases and 2 deaths. . The the health minister for Nigeria 2 days ago said there were 10 confirmed cases and two deaths. .…

So at the time of the story, Patrick Sawyer arrived in Lagos July 20th, so the maximum time that they had to be infected by him and show symptoms is 3 weeks. Frankly 10 confirmed cases from one guy is pretty astounding given that the transmission is bodily fluids. The article states that they were all close to Patrick Sawyer.

Dr. Smith,
I just finished reading hot zone. Let me clarify a couple of things. It is non-fiction. It is not dramatized. It is not a study by any means, therefore citations were not made. However he does quote many phd and md type people. In particular, Peter Jahrling Ph.D, who is the co-discoverer of Ebola Reston which was brought to the US by infected monkeys in Reston, Virginia, and is currently Chief scientist NIAID, emerging viral pathogens section, and who became, after the 1990 Reston outbreak, principal scientidt at USAMRIID. All four monkey caretakers tested positive for Ebola, only one of whom cut himself. They all recovered and were asymptomatic during their infection. Although USAMRIID did not do experiments to verify airborne transmission, it was clear that the monkeys transmitted the virus to each other through the air and hundreds of monkeys were euthanized in the Reston Virginia facility called Hazelton. The caretakers' viral load lessened and eventually disappeared.
Genetically, Ebola Reston and Ebola Zaire are almost identical, and appear identical under the electron microscope. This is what Dr. Jahrling said: ”Why is the Zaire stuff hot for humans? why isn't Reston hot for humans, when the strains are so close to each other? The Ebola Reston virus is almost certainly transmitted by some airborne route. Those Hazelton workers who had the virus- I'm pretty sure they got it through the air.” Reread the last section of the hot zone about the Reston outbreak and see what you think. For everybody else- if you want a vivid description of what ebola can do to a human being, without hyperbole, read the hot zone. It is a hell of a book. I challenge Dr. Smith to find a factual error in the book.

I just read the study, and I agree with you. The sad truth is that Favipiravir is too simple, too cheap to manufacture, not profitable enough. Besides, Zmapp us being developed by a private company through some kind of development contract with the US army.

Rick, just because the Hot Zone may not contain few "factual errors" doesn't mean it's not dramatized. I love the book, but Preston chooses what facts to include and which to leave out, which overall leave the impression that things are much worse than they really are regarding the virus. Ask any Ebola researcher and you'll get the same answer--they cringe when anyone mentions "The Hot Zone" because it's NOT a textbook.

Thanks for your response Rick. Tara... What do you think about my previous post? Am I missing some vital facts perhaps?

Yes, I still think it's not airborne. As you note, close contact with Sawyer...not minimal contact (as in the airplane, airport, etc.) If that was the case you'd expect way more cases. Not surprising that the case count is also currently understimated--I've been talking about this on Twitter for days.

harry, sorry, day job calls. I'm not as familiar with the drugs so beyond the basics I don't have anything to add.

Nah, I don't think it's airborne either. Thanks for the reply Tara!

Ok, so we should be concerned of airborn Ebola if we are around pigs that have Ebola right? Well what happens if the West Africa outbreak gets worse as it appears to be doing so, not because of the deadliness of the decease but more so because of human fear and lack of education. As the disease spreads and more people get infected couldn't the chances of pigs get infected thus creating a spiral of new strains of the virus potentially an airborne version of the disease? I guess that brings me to one question, do West Africans eat pig? Apparently not but that doesn't mean there is some other animal out there that has to potential to do the same...

By Jason Hunter (not verified) on 22 Aug 2014 #permalink

Ok here's a question Tara--why has our US Ebola gentleman been released into the general public if as the Canadian government asserts that Ebola can be transmitted via semen for up to seven weeks. This obviously puts his wife at risk--what if he had a mistress. The CDC who oversees these things should not take these blatant risks. Also has anybody else noticed from CDC reports that this disease is now doubling in number of cases in less than 30 days and accelerating. By that logic we could have 10,000,000 cases by this time next August. Something to consider.

Dr Tara, I read your article and ALL the comments and have to commend you on your handling of questions and queries thus far. Unfortunately there is breaking news of an unrelated outbreak in the Democratic Republic of Congo (DRC) where up to 70 people are reported to have died in the last 10 days of hemorrhagic fever. Out of 8 patients' samples tested for Ebola, 2 are said to have been positive for EVD. Although this appears to have no connection with the West African outbreak, this now makes 5 countries that are dealing with Ebola concurrently. Should we start worrying now?…

Jason, that is a possibility, but remote. Dave, even if he is positive per seminal fluid, that's not exactly putting "the public" at risk. I already wrote about that here if you want to read my overview:… TL;DR: not even a very big risk to his wife. Bob, keep in mind that as of now, it is only 2 confirmed cases, and we're not sure if they're linked to the West Africa outbreak or if these are separate. Obviously DRC has a long history with Ebola.

Dear friends, am glad about the excellent info on ebola. Here are my opinions
1. Ebola is an RNA virus, not a retrovirus, it multiplies rapidly but doesn't mutate to other forms, like being airborne, I would still think it can be spread through air if the air is moist and people in closed room and sweating, since all that is required is just a slight mucosal entry, I would think that the Nigerian doctor who died of ebola could have got it this way. So the word airborne is quite tricky.

2 . The second point is about shaking hands, I wouldn't think for a moment that shaking hands is a risk, how in the world could a virus breach the innate protection we all which way?? so we shouldn't panic over such a thing, yes offcourse see the has to come in contact with an ebola infected person.... again that person has to sweat, and then you shake's safe...and then unless you rub your nose or eyes..perhaps that's when it's pathogenic...We don't know the role of our innate defences at the mucosa like the dendritic cells, neutrophils and macrophages...perhaps they could play a role in preventing the virus from binding on to cells. So hand shakes to me is ok.

3 . Had it been airborne the entire plane carrying the American sawyer could have been infected..If we are to fight the virus..we should fight the panic that is being caused, and in the media they paint a frightening picture that blood comes out from eye balls etc.... that's not true, only ten percent percent of victims experience this...the British nurse who survived ebola said he didn't even vomit..

For a virus to mutate from its current transmission into being airborne is only theoretically possible.. for a pathogen to change course is not usual.

Thanks, samuel kumar

By samuel kumar zambia (not verified) on 08 Sep 2014 #permalink

from USAMRIID 1995,
"Lethal experimental infections of rhesus monkeys by aerosolized Ebola virus"

We also demonstrated aerosol transmission of
Ebola virus at lower temperature and humidity than that
normally present in sub-Saharan Africa. Ebola virus
sensitivity to the high temperatures and humidity in
the thatched, mud, and wattel huts shared by infected
family members in southern Sudan and northern Zaire
may have been a factor limiting aerosol transmission of
Ebola virus in the African epidemics. Both elevated
temperature and relative humidity (RH) have been
shown to reduce the aerosol stability of viruses
(Songer 1967). Our experiments were conducted at
24ºC and < 40% RH, conditions which are known to
favour the aerosol stability of at least two other African
haemorrhagic fever viruses, Rift Valley fever and Lassa
(Stephenson et a/. 1984; Anderson et a/. 1991). If the
same holds true for filoviruses, aerosol transmission is
a greater threat in modern hospital or laboratory
settings than it is in the natural climatic ranges of

So, aerosolized transmission on humane primates of filoviruses is pretty much established.
Maybe, the environmental conditions on equatorial and tropical Africa are not ideal for this route, but it could well be the case, that in colder climates, given the high infectivity shown in this study (400 FPU vs the usual 1×10^4, 1×10^6, or 1×10^8 for Influenza viruses) it could become a very viable route for infection on settings similar to the ones where Influenza viruses thrives, that is, confined, cold and dry spaces common on developed countries.

By Marcos Eliziar… (not verified) on 23 Sep 2014 #permalink

Marcos, I have no idea of your background--do you understand the difference between experimental studies between lab monkeys within the setting they describe, and what actually happens in an outbreak? Hint: they are quite different, as is even noted in the part you quote. It's the pig paper all over again--just because it can be artificially created doesn't mean it actually happens. Just about any pathogen can be artificially put into an aerosol form using physics and chemistry alone, but clearly they all are not spread in that manner.

Thanks for your response Tara.
Yes, you are right and by no means I am trying to create panic or be a scare monger, I am just curious if given the fact that we only have data on outbreaks that occurred in vastly different environmental conditions than the ones that are common in western countries, how EBOV could behave in said different conditions.
So, forgive me for being so insistent, but those are my questions:
As mentioned in that article aren't those experimental settings closer to the environmental conditions on a modern western hospital setting in terms of temperature and Relative Humidity? Could this be relevant in your point of view?

And then, given the high infectivity and the possibility of EBOV infecting epithelial cells on the respiratory tract, couldn't be possible for a patient in such a setting to generate aerosolized particles enough to be infective, should said particles remain viable on open air for a certain amount of time?

By Marcos Eliziar… (not verified) on 23 Sep 2014 #permalink

"As mentioned in that article aren’t those experimental settings closer to the environmental conditions on a modern western hospital setting in terms of temperature and Relative Humidity?"


"Could this be relevant in your point of view?"

No. Here's the thing and why I asked about labs. Creating an artificial aerosol really has no bearing on what's out there in nature, so the first part of your question regarding humidity really doesn't matter, because we have no reason to think that those conditions would ever exist in a real life setting. Our bodies don't work the same way an artificial device does in creating these Ebola aerosols, period, so how they behave at various temperatures and humidities etc. is an interesting theoretical question, but one that has little real-life application. Everything else follows from your first assumption, which is fatally flawed. Vincent's article here may be of interest to you on airborne Ebola:…

I also missed your CIDRAP comment earlier, but they're like a hammer who sees everything as a nail. I'll just say there has been a lot of controversy over that article and a lot of people who were not fond of it and leave it at that.

Fair points Tara,
I see now things from another point of view. I've searched if other institutions went ahead with this position from CIDRAP, and it looks like they have taken an isolated stand.
Liked a lot the article you've linked, but also for a very different reason. As a layman, I always thought that the outcry against Fouchier and Kawaoka with making H5N1 airborne in mammals obscurantist fear-mongering, but couldn't quite explain why I thought so in practical terms. Now I see the relevance of their research and can explain as a layman for other layman why this kind of research is important.
Thanks for your patience Tara.

By Marcos Eliziar… (not verified) on 24 Sep 2014 #permalink

Hiya Marcos Eliziario Santos!
Glad to hear you understand Tara's points about Ebola and aerosolization. However, it's really important to not conflate the Ebola models with what Kawaoka and Fouchier are doing. They're very different scenarios; no one is suggesting that Ebola research is gain-of-function or dual-use research of concern, whereas the flu-related studies are.

I don't want to derail Tara's excellent Ebola-explanation thread on the differences and details, but suggest that you read up on GOF and DURC concerns, especially as put forth by Marc Lipsitch and the Cambridge Working Group.


By Kelly Hills (not verified) on 24 Sep 2014 #permalink

The article published by CIDRAP may draw a slightly alarmist, and certainly costly, conclusion, but it offers literature citations showing that the virus could survive in droplets long enough to be inhaled and that a few people in past outbreaks have been infected through casual, or occasionally no physical contact with a symptomatic person. The reported case where one woman in a taxicab infected four or five other people is a recent example. The news didn't say whether she might have gotten sick in the cab, but surely she didn't vomit directly on everyone around her.

You said we should wait to draw any conclusions from that case until the disease suffered by all the secondary cases was definitively identified, but it doesn't appear that that information will ever be publicized - the health authorities have bigger fish to fry by now - and as far as I know the original diagnoses have not been debunked. Surely the passengers' exposure was less than that which a nurse or nurse's aide would experience. Given that this virus is often fatal, though surely the death rate in a place with good supportive care would be under 60%, and that it seems to spread that readily at least sometimes, I'd sure want to use some kind of protective gear if I were taking care of actively sick people.

Also, reading that kind of article always makes me think I should find someplace other than the shelf above the toilet to keep my toothbrush. Blech.

A newspaper story that "has not been debunked" is a pretty low bar for scientific investigation.

First let me premiss my comment with I am by no means educated in virology nor am I much for the sciences. So with that 1 could a virus be tricked or manipulated to become asymptomatic in a human host? Also can you tell me have there been any studies on the effects on the virus on dogs?

I would think that when Tara says it's not airborne that she would mean though breath not inhalation on vomit etc...Isn't that obvious?

"Michael T. Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota, acknowledged in a recent New York Times op-ed that virologists are 'loath to discuss openly but are definitely considering in private' the possibility that Ebola has gone airborne. Some have questioned why hundreds of health workers have become sick and died from Ebola given that they take extreme precautions to avoid bodily contact with victims."

"there may be something unique about pig physiology that allows them to generate more infectious aerosols as a general rule"

There MAY be? That's comforting.

Scared, you sound like one of those people that will panic no matter what anyone more knowledgeable than you tells you. You worried about something before this outbreak and you'll find something to worry about after this outbreak - whether it's another disease or lizardmen or whatever else conspiracy you fear that gives you some (non)purpose in life.

Just wondered if you had commented on the NIH.GOV article PMC3100998 which under the Heading "TIM-1 Expressed on Human Airway..." includes the following statement: "One established route of infection for Ebola virus is the inhalation of aerosolized particles"?

Robert, that refers to a lab setting. Just about any pathogen can be mechanically made into an aerosol. Doesn't mean they are actually transmitted via that route.

Also, Martha, Osterholm has backed off that (after being told by virologists how unlikely it is). Se for example

"Ebola going airborne would be devastating, says Dr. Michael Osterholm, with the Center for Infectious Disease Research and Policy. But he said such a mutation of the disease is not a big risk.

"A much bigger risk is this virus moving out of West Africa and getting into the slum areas like Lagos and Nairobi and making the cases in West Africa only a small part of the outbreak," Osterholm said in an interview with CNN's "The Lead with Jake Tapper.""

I imagine that pig physiology is radically different than human in the sense that a pig snout has larger orifices, and is predominantly a wet configuration. The content of expelled air would contain larger quantities of non-dry air than humans, even if exhaling via the mouth. To reproduce a similar amount of moist exhaled air, we would need to cough, or sneeze. It is at this point that infectious particles would be distributed, up to 10 feet from an infected person. With a 16 hour life on fomite surfaces, this provides a bit of a window for risk. The NBC cameraman that became infected says he thinks it was a result of assisting in the decontamination of a transfer vehicle used to transport an infected patient. That would mean he came into contact with the fomite variance, but then what? Wipe his face? Inhale air droplets?

By Patrick Nolan (not verified) on 09 Oct 2014 #permalink

What about: and ???

Clearly, aerosolized Ebola can infect the lungs. The only issue is the aerosolized viral load put out by someone who is sick. I would tend to think that someone with the Flu could generate a similar or worse aerosolized viral load compared to the pigs in the aforementioned study. This will be a significant problem.

By Sam Bernstein (not verified) on 15 Oct 2014 #permalink

If the virus proteins mutate will a vaccine be useless?

Are we sure it's not airborne? Well... Just as a population may contain a statistical outlier, such as how the human population contains a few people who can multiply faster than a computer - so to, then, there are people whose systems will be statistically different enough from normal that they could aerosolize anything. But I feel that is localized and rare. If you are really curious about ebola being airborne, cia has a paper by james petro called "mitigating threats from bioterrorism". In this paper in the second bulleted list, Mr. Petro discusses how scientists at the university of pennsylvania created a special virus that would help treat leukemia patients. It uses the surface proteins of ebola combined with parts of HIV plus some cool genetic engineering. This way they were able to spray it into the lungs of leukemia patients (aerosolization) and the little viruses were able to repair a certain type of genetic damage. You see, Ebola and Hiv both share the exact same budding technique, about as rare as lightning striking the rose bush you don't have in your front yard 50 times. Anywho, oh! where are my manners? Here is the link.…
Finally-er, many moons ago, there was this man that was very bad. His name was shoko asahara. He led a cult and they were the ones behind the sarin subway attacks in tokyo. Well, this wasn't enough for our little friend, so he starts a multi-million dollar research lab and breeds weaponized anthrax, and still wasn't happy, so he actually sent a team to south africa to find live samples of eeee-bola. Unfortunately for them they used digital communications systems running across eshy's backbone, and apparently as soon as they stepped into the jungle they met a very untimely demise.