This discussion has been going on for some time, and a handful of recent events have prompted me to jump into it (beyond a simple comment or two). First, I saw a bunch of yammering among various biology teachers about this topic. Then Michael Osterholm wrote a well intentioned but seemingly deeply flawed opinion at the New York Times, then Dina Fine Maron wrote an excellent piece at Scientific American deconstructing Osterholm's piece, then the latter two (and more) were summarized and expanded on in a post by Ann Reid at the NCSE.
Here, I will expand on this by applying first principles from evolutionary theory, organizing our thoughts in Tinbergenesque Terms.
There are four categories of reasons that Ebola won't go airborne. I'm going farther out on a limb here than most others, who say things like "it is possible, but..." Imma say it just isn't going to happen. Technically, over time, the Sus lineage of mammals (pigs) could give rise to a flying form, like what happened with some earlier lineage of mammal that gave rise to bats. So what I'm really saying is that Ebola will go airborne when pigs fly. Both are possible. But if that is what you really think of as "possible" instead of just "no, it won't happen" than you may need to calibrate and stop buying those lottery tickets!
Here is why Ebola won't go airborne.
First, diseases in general, including viruses, do change which species they infect sometimes, and they change in virulence and the exact effects on the host, but they really don't change their mode of transmission. At the largest evolutionary scale there have been some novelties, obviously (or there would be no variation!). I am pretty sure many of the influenza viruses are not transmitted through the air, but the only ones we bother to name and study do, and are a subset of a larger group that transmits via water. I may have that wrong (going on old personal communications here) but if I am wrong that just crosses off Influenza as a virus that changed mode of transmission. Ebola is in a large group of viruses that are actually found in plants. Obviously, there was a change in transmission at the origin of Ebola. But really, this does not happen very often. If you can think of examples please tell me. (For a non virus example, Malaria is transmitted the same way all the time even if it changes (rarely) which species it affects or otherwise evolves like crazy to stay ahead of interventions.)
In short, we expect strong phylogenetic inertia in mode of transmission.
Second, there is no in place mechanism, probably. Ebola does not infect the tissues it would need to infect to make its way into a sneeze or cough. That would require a major change.
Third, developmentally, the first step in a virus's life cycle is getting itself into a cell. Airborne viruses need to have a key that matches a lock on the outside of respiratory tissues. So Ebola not only lacks the means for getting out through a sneeze or cough, it also lacks the ability to do much if it did.
Fourth, it is not adaptive. Yes, a virus can mutate to do something stupid and maybe get a Darwin Award, but the chances are at least somewhat reduced. Ebola is very deadly in humans. Humans and the animal vectors that may stand between fruit bats (the likely wild host) and humans are not good hosts for Ebola. The chances of Ebola evolving to infect an unsuitable host are reduced.
Phylogenetically unlikely, mechanistically unlikely, ontogenetically unlikely, adaptively unlikely. Evolution is like baseball but slightly different. Four Tinbergen Strikes and you are out.
Now, the usual arguments in favor of Ebola doing the Hollywood thing rely on references to other viruses, like Influenza. Well, Influenza is way different from Ebola in its reproduction. It has a whole way of evolving that Ebola does not have. In fact, the differences is greater than, potentially (and rarely, but not never) the difference between evolution under sexual reproduction and evolution under simple replication. If two different Influenza strains infect the same cell, they can recombine (reassortment) to make an entirely novel never before seen Influenza. That is a very big deal and is thought to be the primary mechanism for the evolution of novel dangerous flu strains. Ebola does not do that. Ebola can't do that.
Ebola does not do that. That thing Influenza does.
I said that twice. Now I'll say it another way. Using Influenza evolution as a model for Ebola evolution is like using Primate Behavior as a model for Sea Slug Behavior. In other words, it does not fit.
Will Ebola go airborne? No.
ADDENDUM
I'm adding a bit more because some are still missing the point. This is an analogy that I think might be helpful
Cars fly, and airplanes drive around on the ground. Ebola can possibly be transmitted across space in a closed room from one person to another, and you can catch a flu by having someone with the flu bleed directly into your nose*.
But really, airplanes are vehicles designed to fly, they only drive around on the ground a little. They have wings, special engines, an overall shape and design that is adapted to flight. But really, cars only fly into the air now and then, and it is generally an accident.
An airborne virus replicates in high numbers in respiratory tissues, and causes the lysing (or some other process) of cells to allow itself out into mucous tissues. It is able to survive in mucous tissues, and then it is able to survive in aerosolized droplets. An aerosolized droplet is not a bit of bodily fluid cast into the air, it is not a drop of blood shed from a wound or bleeding eyeball, or a loogie. It is a bunch of liquid (mainly water) molecules coherent at a size sufficiently small that air currents are more important then gravity, so it becomes part of the atmosphere, and a virus may or may not be residing in it. Then, and airborne virus needs to have the external morphology that links up with a receptor site on respiratory cells in the individual subject to infection, and then, it reproduces mainly in that tissue.
Ebola is none of these things, except possibly one. Ebola is known to survive in mucous tissue for some time after it has left an infected individual. This is not the same as surviving in an aerosolized droplet, but it indicates the possibility. But to go back to the car-airplane analogy, that is a bit like saying that some cars fly farther when they leave the road during an accident.
The distinction is very important. Jane, commenter below, has oddly implied that I'm not taking Ebola seriously. I would like to point out that I may have been the only person to complain about and argue against the trope that Ebola is not so bad because it is not Malaria. I may also be one of the few bloggers writing about Ebola who has lived in Ebola country, doing health care work, and who has actually worked on the problem of the natural reservoir and contributed to it. I am also one of the few people writing now who has pointed out that even though most people with Ebola are in a few African countries, where this needs to be taken very seriously, that it is also true that those communities, in West Africa, are global. This is how my neighbor, Patrick, managed to die of Ebola. He was an American who also worked for the Liberian government, and was in Liberia taking care of his sister, who died of the disease. His wife and family are here, in my town. Ebola affects communities that are not separate from those who have the privilege of being able to muse about it. And here is where the distinction becomes multi-dimensional. All the talk about airborne transmission is not scientifically grounded, and it is a distraction. But saying that it will not become airborne is not saying that it is not a horrible disease that is highly infectious and has pandemic potential. This, the nuances of the epidemiology of Ebola, isn't really that complex, but sadly, it is a bit too complex to be well managed by the press and others talking about it, in many cases.
And, the distinction is huge. Conflating the very small number of possible infections "across the room" (which are speculative but possible) in prior outbreaks (which, Jane, were not in East Africa) with an airborne mode of transmission is like working out transportation policy for the US but mixing up the part about how cars don't fly and airplanes do. I really think Ebola is not going to become airborne. But if it was airborne, the whole ballgame would be very very different. That, however, does not mean that Ebola is not a very serious thing that needs to be addressed. Also, the utter failure to address this by the systems in place tells us that we as a society/species/collection of governments are unable to address a serious public health crisis even if we were under the impression that we were. Trading in misinformation and badly conceived ideas of what is happening or what could happen sets us back, it does not move us forward.
More on Ebola:
- Two Ways Hollywood and Literature Have Confused The Ebola Problem
- Ebola in Dallas Texas: Is our response adequate?
- Ebola Will Not Become Airborne And Here Is Why
- Has the Ebola Death Toll Surpassed Malaria in West Africa?
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*Actually, this may not be true, to my knowledge no one has considered this, certainly not tried it!
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IT HAS ALREADY... so do more research !
No, it hasn't.
There is a frustrating amount of ignorance about the mechanisms of evolution even among the top news and opinion outlets. This combines badly with hysteria over a scary epidemic. I've recently written a bit about this:
http://monkeysuncle.stanford.edu/?p=1463
and
http://monkeysuncle.stanford.edu/?p=1443
It was refreshing to hear Pardis Sabeti actually use the terms "evolution" and "adaptation" on The World last week:
http://www.pri.org/stories/2014-09-24/scientist-cutting-edge-ebola-rese…
Aldo, Jamie, Ebola is not entering the human setting again and again, or continuously, as a diversity of different genomes to be tested by selection. The outbreak is a single genome to start with, diversifying, but starting with zero diversity.
Dithering about whether it's "airborne" or just "aerosolized", as the people wearing eyeshields seem to believe, is a good way of silencing the more hysterical but also brushing under the rug the fact that you do not, indeed, have to handle vomit to be infected. In previous outbreaks, a few people were infected just by visiting relatives in the hospital and having casual, or rarely no, physical contact. In this one, multiple people have been infected by sharing public transportation with a sick person. I don't think they'd agree that if they were infected through droplet contact with the eyes, or through the mouth after droplets landed on their skin, or what have you, rather than through inhalation, then there's no need to worry about it spreading too easily.
Jane, you are very wrong. The difference between being airborne vs not can not be described as dithering.
I don't know of any reported and evaluated cases of transmission of any kind for this outbreak. I'm not saying you are wrong but you'll need to back that up with a reference.
Ebola is very infectious. It does not have to be airborne to be very infectious. But if Ebola was airborne there would not be 6000 or so infections. It would be in at least a dozen other countries and millions would have it.
By the way, I don't think they should be letting people from the region onto airplanes without testing.
It seems that people need to have the constant threat of airborne infection or Ebola doesn't count.
We are un prepared for this type of outbreak in the usa. Try staying off Internet for a day. Fast for a week. Kill to eat.
As a sick vet from chem warfare I say you don't know and the .gov crowd does not give a crap about you. Maintaining the equipment and avoiding contact with NBC weapons or naturals is difficult. Try drinking water at MOPp4 or level A.
Science is the answer you are right about that but our populace is mostly ignorant.
I am a "conspiracy theorist", and i see a lot of hype regarding the spread of ebola... I wish other people were more willing to actually look into the disease, rather than scurrying to believe it has become airborne. As you stated, if it were airborne, then we would have already have a huge problem on our hands, and most like have a worldwide pandemic... but its not ..
Come on. Let's not be stupid all together. Ebola virus is secreted in blood and saliva, and you have both in your mouth. Both are given out in copious amounts when we cough and sneeze. There are already reports of possible aerial transmission. Wait and see when the annual flu epidemics enters the same area with everybody sneezing and coughing around..
Excuse my ignorance, but what about if Ebola and Marburg infected the same cell simultaneously...?
This essay is just a collection of strung together conclusions. Limited evidence provided. Weak analysis.
The conclusion may be correct, but the writing does not support it.
Craig, good question. The way they reproduce is different from influenza, so nothing would happen.
Erkki, there are no confirmed reports of airborne transmission. Airborne transmission does not happen just because Ebola is in saliva. Other things have to be in place as well.
Oh dear, I'm not just wrong but very wrong! Unfortunately, that's not a factual statement but a value judgement. The question I raise is not whether Ebola is airborne or not - it isn't - but whether, if it is contagious enough in certain common circumstances to spread exponentially in the literal sense of that word, the fact that it isn't airborne should be taken as comforting or reassuring. My opinion is that an R0 higher than that of flu, which those in the more sanitary developed world are all supposed to fear enough to get vaccinated against annually, in a disease of this severity is bad news for the public in affected areas no matter how it is achieved.
You can easily find the publication relating to transmission in past East African epidemics. Since this one is still unfolding, writing journal manuscripts that duplicate existing knowledge isn't on the priority list of people on the ground. However, we have been told of cases in which people on public transportation have infected multiple fellow passengers, and the doctors actually working there, who ought to know more about it than either of us, have expressed dismay that people who can't get into treatment facilities go home by taxi and may infect others while doing so. Now you and I both know that a taxi ride in Africa is not the same as a taxi ride in the U.S., but they're talking about at most casual contact or indirect contact via droplets on one's face or fomites, not sex or washing one's hands in somebody's blood.
On my favorite blog this week - one I suspect you wouldn't consider reading, unfortunately - commenters started discussing Ebola, and one of them insisted that it couldn't become a pandemic, because it can only spread this easily in poor, crowded and unsanitary places. The blogger and a fellow commenter immediately jumped on him, saying: Do you have any idea what percentage of the world's population lives in such places? (Hint, well over half.) The don't-worry-be-happy rhetoric - which may be motivated mostly by the feeling that a binary opposition to racist fearmongering is needed - sometimes skews towards saying that something isn't a real pandemic unless a lot of white people are dying; that won't happen with Ebola; therefore, hey, no problem!
Jane, see above, addendum.
I see the addendum above, Greg, and you have my sympathy for the death of someone you knew in this outbreak. One assumes you are not among the Pollyannas, given that. But it seems like some people are vehemently opposed to the mere possibility that filoviruses may be transferred directly or to fomites by droplet, even over a short distance, and never mind that epidemiological literature suggests it can happen. That says to me that many people, for one reason or another, just don't want to believe it.
But for the public, the crucial point is that you do have some small but non-zero chance of getting the disease if you spend much time in a taxi - flying or otherwise! - with a person who is sick. I suspect the public cares less about the mechanism than the fact.
On a minor point, I disagree with any suggestion that Uganda, which is the formerly "major" outbreak location that always comes first to my mind, is not in East Africa. I agree that the DRC, the other major outbreak location, is not in East Africa, so that was careless speech on my part. If the regional location of Uganda requires a value judgement, we can agree to disagree.
Jane:"But for the public, the crucial point is that you do have some small but non-zero chance of getting the disease if you spend much time in a taxi – flying or otherwise! "
Non zero, maybe near zero, but unknown and Ebola is serious stuff. I for one do not like the strategy of just checking for fever for people getting on long international flights. The Texas case is a good example of how that kinda worked but not really, not good enough.
Uganda is is East Africa by my reckoning, but most ebola has been in CA. Having said that, western Uganda is very central Africa, and the eastern Congo has shades of east Africa. For example, the lingua Franca in E. Congo is a form of Swahili, but with more French cognates and almost no English cognates. People in w. Uganda speak the Congolese version.
Fair enough.
There seems to have been a minor breakdown in Dallas, when he entered the hospital the first time. News reports say that
He was sent home from that visit with antibiotics, and returned two days later critically ill.
At any link of the chain where people are involved, the chance of an error is non-zero, apparently.
An informal observation: I watched several news stories about this today. Several of those stories included interviews with, or reports from, doctors from CDC or other facilities. All of the doctors clearly stated how Ebola is transmitted, and clearly stated that it was not as easily transmitted as the flu.
The news reporters, however, merely referred (several times) to the concern and "possibility" of the disease spreading from the newest patient to people he was visiting and those he may have encountered on the street, with none of the caveats given by the doctors. I wonder which message (difficult to spread vs fear of spreading to those simply because they were close) will be remembered by many viewers.
This is the crux of the confusion. Not airborne does not mean difficult.
What modification allowed ebola reston to become airborne
Mark, good question.
The mode of transmission of Reston is not entirely clear. It is an Asian virus, like Ebola but not the same thing. It is not a form of Ebola, but a related disease. It is not the case that Reston was a non-airborne virus that became an airborne virus. We don't even know that much about it. It is rather mysterious. It is probably the possibility that Reston was transmitted over the air (but in relatively close quarters, not clearly "airborne") that in part led to the dramatic what if stories concerning Ebola. But that is mainly a matter of building an unlikely scenario on the basis of a lack of knowledge.
Great blog and fair points. My only point is it is in the genus Ebola virus and is a a filovirus that is airborne and humans were infected with it and there are new strains (which we don't know a lot about) circulating in Africa so while albeit very low low chance of ebola going airborne it is theoretically possible. Thanks for your info.
FYI... sorry to burst your bubble.
http://www.telegraph.co.uk/news/worldnews/ebola/11135883/Ebola-could-be…
In a world of randomness... you lose.
Dallas case:
Saturday (20 Sept) Subject arrives in the U.S. from Monrovia via Brussels and Washington, D.C. with DFW destination.
Wednesday (24 Sept) First symptons appear
Friday (26 Sept) Patient self-reports to (Texas Health) Presb. Hospital of Dallas (locale: Vickery Meadow/Walnut Hill section of north Dallas); seen, examined and released (with medical prescriptions)
Sunday (28 Sept) (patient vomits in apartment complex parking lot / 10:30 a.m. Dallas F.D. EMTs respond and take the patient to Presb. Hospital.
Tuesday (30 Sept) Tests return "positive" results for Ebola; ambulance used two days previously taken out of service.
---
Man on the moon, how is a link to a Telegraph article an argument against the specific points I made in this post? Please feel free to address them!
Yeah, the more I hear about the Dallas case the more I want to take the "kinda" out of that previous comment and put in "dind't" (might require some rewrite)
At the larger scale we can almost certainly not have a Liberia like situation. Ten years ago, maybe not even in Liberia, but their health care system got wrecked by a civil war.
But short term I'm not developing a lot of confidence.
“Ultimately, we are all connected by the air we breathe.” – CDC Director Tom Frieden, Press conference on the first diagnosed case of Ebola in the US on September 30, 2014.
I'm so confused.
That was not a comment on Ebola being airborne. So you have no reason to be confused, Tim!
On Dallas: http://scienceblogs.com/gregladen/2014/10/02/ebola-in-dallas-texas-is-o…
Thx, Greg.
I'm still very, very frightened -- I'm a conspiracy nut.
What is the difference between a virus and a parasite? I am not a doctor but this seems to act more like a flesh-eating parasite than some kind of viral "disease"... some say that viruses are parasites but since the converse isn't true I don't know why they would confuse the two...
A parasite is an organism that takes energy/resources from a host and does not return the favor. Since a virus uses sells in a host to reproduce, and typically does not repay the favor, a virus is technically a parasite by a strict definition.
In practice, the term parasite is usually reserved for actual organisms and viruses are rather annoying in being not exactly organisms.
It is, in fact, a little confusing.
Greg, saw a snippet of a network morning show this morning and that attention whore Dr Oz was on there telling Matt Lauer that it was a certaintaty that ebola would mutate to become aerosolized in delivery. Dr Oz's drivel is likely infectious though.
What about the fact that Ebola crystallizes and deactivates itself when not actively infecting tissues? It has been said that Ebola is neither living nor dead. Is it possible that smaller crystalloids could "exist" in aerosolized droplets? And if so, could Ebola not create larger crystalloids? Certainly this has been seen within the livers of dead subjects, perhaps in a means to conglomerate and self preserve? If so, is it not possible that these crystalloids could reactivate, reduce size by separation from the central mass, and spread exponentially in a new host?
Not really, and that does not address the lack of receptors in the history.
I don't think viruses can ever be considered parasites: They are not living organisms. They are VERY sophisticated collections of complex molecules that have biologically significant properties, but they are not alive. They do not respire, they do not ingest, digest, or excrete chemicals to sustain metabolic processes, they do not reproduce (even though a host cell that *is* alive can replicate the complex molecules and assemble them into a copy of the original), and they do not grow, age, or do anything else that's associated with living cells or organisms.
Parasites, by contrast, do all these things, and also happen to 'feed' on other organisms for sustenance -- without killing them beforehand or (immediately) as a consequence of "stealing their chemicals" to provide materials needed for their own metabolism.
Viral "particles" don't fit the bill. They happen to contain genetic material, and their presence inside (some) living cells induces those cells to make copies of the particles, but that is far, far from any definition of "being alive".
"He was sent home from that visit with antibiotics,"
Do antibiotics in Dallas kill viruses?
He was handled. A black man in a poor clinic in a poor neighborhood. There is a life expectancy difference across color lines and across income lines. This is partly why, I'm guessing, though I don't know a lot about this particular hospital. But I'll be he was just one of the many people who were handled that day.
Brainstorms: Right. Parasitism is one of those words (commensalism, mutualism, etc) that expresses a relationship in simple well defined terms. If you had to put a pathogenic virus into one of those categories it would almost certainly be in the "parasitic" category.
The term Parisite, though, is usually used for organisms.
I don't agree with all the things you said, though. The word "reproduce" applies. They do a thing and after that there are more. Aging is not universal among organisms.
They do use an organisms resource to reproduce.
I haven't looked, but I imagine a scholarly book on "Parasites" would either have a chapter on viruses but cover all the viruses in one place with an apology that some might not think it appropriate, or a lengthy treatment in the introduction as to why there is not chapter on viruses!
So should we be concerned with the onset of flu season? I know you stated as much in your article but with the flu being highly contagious and spread through the air, is there any possibility that the flu virus could somehow alter its structure in someone infected with Ebola and mutate in a way that it becomes more easily spread? I've never gotten a flu shot in my life but I'm kind of considering it now...
Marisa, I would love to come up with an additional compelling reason for you to get a flu shot because you should get one!
The Influenza virus and the Ebola virus are not going to interact. By the way, flu has probably been all over the place in West Africa all along anyway.
I would imagine that someone with the flu who is then infected with Ebola would have a hard time, though. Seems like having those two things at once would be bad.
Greg,
a few points: First, ebolavirus has indeed been shown in the laboratory to be transmissible via "airborne" routes of transmission. Second, perhaps it hasn't been seen to date due to the nature of the geographical context of the previous outbreaks--they have occurred and been restricted to warmer climes (exception of related Marburg). It is untested and unknown what will happen in a temperate climate in the winter months--when most "airborne" bugs are most stable in the environment. Third, the moi of ebola is extremely low at 1-10 organisms (this is incredibly low). Fourth, ebola has indeed been recovered from naso-pharyngeal tissues of lab-infected pigs, so your argument that it does not infect tissues needed to be transmitted by a sneeze is not correct. Lastly, it is taken into cells via endocytosis and does not need a specific receptor to bind to. Yes, Greg, your pigs may be able to fly soon. stick to your expertise.
Link, if you take each of your points one by one and compare them to what I say in the post you'll see that my argument stands. Is it just that you did not read the post carefully?
I am actually kind of an expert on evolutionary biology and I've been working on the Ebola thing as a bit of a side line since doing some related field work in the 1980s. You, on the other hand, are a TV chimpanzee, though I admit a mighty impressive one. How's Mata Hairy doing, by the way?
"Ebola affects communities that are not separate from those who have the privilege of being able to muse about it."
Good one.
Jane is correct about there being a need on one hand about it being important to calm people down and to not promote hysteria/panic, but on the other hand not trying to trying to sweep modes of transmission under the carpet. While I don't believe anything like 12 Monkeys is possible, I do think it is best not to be glib about the potential for subtle and yet significant changes in infectiousness to occur when an epidemic reaches a certain critical mass — enters into dense population centers etc.
I think there has to be a happy medium centered on what we do and don't know — and circumspection about the limits of our knowledge.
First off, you address this a little in your addendum, but people need to understand the difference between airborne transmission [meaning a microbe that can remain viable and infectious in the air for a prolonged period — for instance, MTB droplet nuclei can swirl around in a room with poor ventilation for more than 24 hours] and droplet transmission in close quarters. To date, many studies have shown that ebola virus is not really stable/remains infectious outside the body for long (or only in certain conditions. But there is no reason to believe that Ebola virus (in saliva, mucous, blood when patients with haemoptysis or vomit) cannot be aerosolized and inhaled in close quarters — and most of the literature lists this as a possibility. It can also be aerosolized by cleaning procedures, etc, which is why it is recommended not to use water hoses for clean up. True monkeys in cages don't seem to be able to transmit the virus over short distances, but I've seen too many infection control presentations on how well humans can expectorate to feel confident about those observations. Both Ebola Zaire and Ebola Reston have been documented in the nasopharyngeal secretions of pigs, and we know that the pigs at least must have been able to aerosolize that well enough to transmit Ebola Reston to monkeys. I have to track down the citation, but there may have been concurrent respiratory condition, but concurrent respiratory conditions are common in humans. In sub-Saharan Africa, TB is epidemic, and community acquired respiratory infections common, particularly among people living with HIV.
In short, I'd say N95 masks are a reasonable precaution for the non-exposed in ALL health facilities, and maybe any other congregate setting. UV lighting and good ventilation too. It is just common sense.
Regarding documented cases of viruses changing modes of transmission. That is true, there aren't many, but there appear to be some, particularly, if you expand to non-human viruses. But there are questions even there because we haven't really had the tools to study mutagenesis and phylogeny very long, so maybe some of those viruses already had the capacity to be airborne before the period of our observation. Foot and Mouth was once thought not to be airborne right?
But the virus that has been most studied, HIV, clearly has not changed modes of transmission. It has however, changed in the efficiency of transmission/infectiousness adapting to different populations and risk practices, and in the use of cell surface receptors (the chemokine receptors — not the CD4 receptor) and in the range of cells it can infect. But those only require subtle incremental mutations... But subtle changes in viral properties do occur — and it isn't all on a path towards less pathogenicity.
Now, re whether infection can be caused by inhaling Ebola. True, Ebola doesn't infect alveolar cells, it is believed to first infect people by attaching to receptors on endothelial cells. But there are endothelial cells in respiratory track (in the mouth, in the esophagus, in the bronchi) and someone should tell these virologists that there are even endothelial cells in the lung — they are an essential part of the architecture. Reaching endothelial cells in the lung is really not difficult in anyone with any respiratory condition. Once again. Are people in Africa likely to suffer from respiratory problems? Well, yes, actually. And who else might be more susceptible to infection via inhalation? People with asthma, bronchitis, smokers, people with TB, people living with HIV (with LIP), people with COPD, people exposed to indoor pollution.
Back to ontogenetics: Viruses do mutate incrementally to latch onto other receptors, and usually only expand their repertoire to receptors that are similar to the ones they already infect.
But there is a lot we don't know or understand here. To infect cells, EV's glycoprotein probably has to bind to a cell surface receptor, though there are a number of papers suggesting that host factors, including antibodies to the virus, appear to help mediate the process.
But to my knowledge, at present, there are two primary candidates for cell surface receptors that EV might bind to: TIM-1 — which is on expressed in human mucosal epithelial cells from the trachea, cornea and conjunctiva — appears to be the critical receptor for the acute infection process, However, other receptors must be necessary in other cell types the virus infects. Recently, studies have shown that TIM-1 is not essential for EV to infect macrophages.
Using the rule of mutating to use similar receptors, TIM-3 (on activated CD4 cells) and TIM-4 (on macrophages — including alveolar macrophages — and dendritic cells may be reasonable receptors a mutation could permit or that it might be able to use already. There are a number of papers looking at the role of TIM family of receptors.
Other studies have suggested that Niemann–Pick C1 (NPC1), a transmembrane cholesterol transporter protein, is critical for viral entry — but it might be more involved in intracellular transport of the virus, early post entry. [Sort of the CCR5/CCXR4 etc for Ebola]. NPC1 is NOT restricted to epithelial cells. But again, I think it is an accessory receptor and perhaps only comes into play if there is a TIM-like receptor, or something else that the virus first binds to. I don't know enough about the structure of TIM yet to know whether there is any significant structural homology with other receptors. Nor have I seen much in the literature
My point is, there are a lot of question marks over all of this.
But no, if it only binds to TIM-like receptors, Ebola is not likely to be able to fit a squeeze a round peg into a square hole via a mutation or two... But I don't hear anyone giving specifics about the binding properties of the virus or its targets — every one speaks in generalities, I think, in large part, because we don't know for sure. The literature re TIM and NPC1 is all from the last few years.
So I think some circumspection is in order.
Re Ebola not being adaptive — I've always thought that sounds more like wishful thinking than a law. Do you mean the virus sees humans as a side trip from bats? A virus doesn't care about its host — it is driven to replicate and spread wherever it can — and the more of it around, the more likely it will find a gap to get through — a way for the. Adaptive mutations are more likely to occur once replication reaches a critical mass in the right setting. It may first mutate to kill less quickly, because that would be one way to improve its chances of being spread — that might be an easier way to adapt than dramatically changing receptors but there is no reason to feel confident about the virus not adapting in the current situation. It has all the hallmarks of situations where we have seen viruses adapt before [poverty, people living in congregate settings, increased mobility, and potential cofactors — no one is discussing the possible role of HIV or other viruses in this context].
Really, that is insulting to anyone working in the HIV field. The virus is not looking for a way to get back to chimps and macaques. It has greatly expanded its range by moving into humans. Sure, if left to its own devices (and we aren't allowing it to), it may become less pathogenic over time — but that could take awhile.
So forgive this long rambling thing. All I am saying is that it may be doing health care workers a disservice to tell them to only worry about physical contact. I think it would be wise to take infection control up another notch. If you saw Jon Cohen's pieces the other day, too many health workers are unsure of how they got infected, and think that they were only exposed in what they perceived as low risk situations. But I think if you have enough people with Ebola in a confined space, N95's have to be worn consistently, and it should be stressed in messaging, because they are uncomfortable, and people don't like keeping them on. As for the general population — in the epidemic settings, I think there need to be precautions in congregate settings and other community IC communication — which will not be easy given the distrust people have of the health facilities. I really wonder what people with other health concerns are doing in those countries at present.
"Re Ebola not being adaptive — I’ve always thought that sounds more like wishful thinking than a law. Do you mean the virus sees humans as a side trip from bats? A virus doesn’t care about its host — it is driven to replicate and spread wherever it can — and the more of it around, the more likely it will find a gap to get through — a way for the"
My point here is mainly that humans are usually, more or less, a dead end for Ebola, and the "life" history of Ebola in humans doesn't present much in the way of adaptive opportunities.
Think of this more broadly: If ground mammals that do not share space and slimed on food like fruitbats (and lacking other features of fruit bats) were likely places for Ebola to take residence, i.e., be selected to survive long term in, there would probably be reservoirs in any of the 50 or so species of primate or ground animal that we suspect can be cross infected but that we know are not reservoirs. On the other hand, several species of fruit bat are apparently reservoirs. To understand the adaptive argument better, one could explore the fruit-bat vs. antelope/primate/mongoose/etc differences. It may be lifestyle, diet, distribution, or something basic like the molecular underpinnings of cell receptor sites.
Intensive research should be done in the Philippines/Indonesia to run down Reston or its kin. There may be answers to some of this there.
Forgive the typo's I hit submit too soon.
Ok, because it reaches a rather pathological dead end in humans, or people mount a successful immune response. It kills too quick. I'd think that the adaptive pressure then would select for less pathogenic virus, or a virus that kills more slowly, and allowing the virus to have more opportunities to be transmitted. But that can happen over time if we don't respond effectively and quickly. Note — humans are much more mobile than other potential hosts, so our own behavior could change the equation.
Re Pigs:There is this paper, which actually involved transmission of ZEBOV from pigs to non-human primates: "The segmental attenuation and loss of bronchiolar epithelium and the presence of Ebola virus antigen in some of the respiratory epithelial cells in the lungs of all macaques suggest that the airways were one of the routes involved in the acquisition of infection, consistent with previous reports."
http://www.nature.com/srep/2012/121115/srep00811/full/srep00811.html
And this paper looks at ZEBOV primarily as a severe respiratory infection rather than a fatal systemic infection in pigs — whether they or other porcine animals could serve as a reservoir or potential reservoir isn't really clear, but it looks to me like they might be midway between what happens in bats versus what happens in humans http://jid.oxfordjournals.org/content/204/2/200.long
Theo, selecting for a lower virulence is what can happen in theory.
Fruit bats are pretty mobile.
Right. Keep in mind that Southeast Asian monkeys seem to be doing something with Ebola in the wild. I'm pretty sure the wild pigs of Africa were looked at as a host, or at least, bush pigs were, and found wanting, but one might worry a bit about domestic pigs.
Now that I think about it I'm not sure if anyone has looked at Central or West African domestic pigs. There are not many of them, just here and there.
My opinions only:
Terminology is important. As I understand it, Legionnaires' disease is not airborne, yet the original cases of this disease were traced to air conditioners. It is apparently spread via airborne water droplets from the cooling units, but is not airborne?
Any germ that kills 100 percent of infected people over a short period, will go extinct almost instantly. All germs, allowed to spread naturally without human interference will render themselves increasingly benign over time. Germs are as bison on the prairies; those bison that overgraze the habitat will die off sooner than those bison who possess more cleverness and restraint.
In my personal view, Ebola lies somewhere between AIDS (not contagious) and the common cold (very contagious). Ebola is not as hardy outside the human host as Hepatitis for example, but hardier than we would wish to see.
Any thoughts about how some medical workers contracted Ebola in Africa, in spite of wearing moon suits and following strict protocols? Is there some method of transmission of the Ebola virus that we have overlooked? Just asking.
Mr. Noatak: Yes, terminology is important. Good question about Legionnaire's disease.
Note that Legionnaire's disease is a bacterium, while Ebola is a virus, which is an important difference.
An airborne disease is a disease that is normally spread from one person to another by transmission in aerosolized droplets. So, the pathogen has to reproduce and be common in respiratory tissues, it has to survive in the aerosolized droplets, and it has to be catchable by a second person usually because the pathogen has a way of getting into respiratory cells in that person.
Ebola has the middle characteristic; it can survive outside a host pretty well. It does not have the first and third characteristic in humans, though in other organisms it might. But that matters. Airborne transmission between pigs is not the same as airborne transmission between humans if we are asking about humans (and the former is not proven, just possible in some unusual cases, maybe).
Legionnaire's disease is not transmitted between people at all, so it can't be considered "airborne." Rather, it lives in water under certain conditions, and when that water is aerosolized (like in a humidifier) it can then infect people who breath in that air.
The distinction is important because knowing the transmission mode of a disease is central to managing it. We don't want to call Legionnaire's disease airborne because that terminology .... airborne ... means transmission from person to person over sometimes long distances through the air. The disease is not transmitted that way so it is not airborne.
I don't think a one dimensional scale (i.e., running from HIV [AIDS is not a contagion, you mean HIV] to the "common cold" [which is a collection of viruses, so that term is also a bit iffy]) is all that helpful. The mode of transmission of HIV and a rhinovirus are not different because of some feature that is more or less of something, but rather, because of very different modalities.
Not being airborne does not rule out indirect transmission at all, but indirect transmission via bodily fluids and airborne transmission are simply very different things.
Interestingly, the flu (Influenza) is transmitted like Ebola is ... direct contact with bodily fluids, i.e., person A sneezes into person B's nose while they are breathing in. It is also transmitted, as is Ebola, by indirect means, where a person gobs on their hand, then shakes someone else's hand, and that person rubs their nose. Or the person with the gob on their hand uses a doorknob, and someone later comes along and uses it, and then rubs their nose. It is also transmitted via aerosolized droplets, unlike Ebola, and thus is airborne. But it is quite possible that most people who get the flu get it from direct or indirect transmission, not through the air. In fact, Influenza does not do so well in the air; conditions have to be favorable for that mode of transmission to work. (The relative contribution of these different modes of transmission is unknown for Influenza.)
Keeping that in mind, imagine treating people with the flu in hospitals in the absence of vaccines. A lot of hospital workers would get the flu, but a good number of them would get it from direct or indirect transmission, just as they might get Ebola if they were treating Ebola patients.
For Ebola, you wear the face mask to avoid direct transmission from a person who is shedding bodily fluid out of more orifices than usual. You wear the gloves to avoid indirect transmission. The system breaks down, you get some on you anyway. Have you ever worked with a contaminant where you need to wear gloves? Essentially, you need to use the gloves to take off your gloves or you end up touching the outside of the gloves. It is very easy to mess up. You have ick all over your gloves, you use one glove to take off the other, then you reach under the cuff of the second glove and grasp a bit of it, then pull that off and toss it out. But when you do that you miss and it bounces off your leg and now you have kooties on your pants. Or the glove snaps a bit and some fluid on the gloves flies over to your ungloved hand. Or you accidentally mess up the order of things and stick your infective finger from one glove under the cuff of the other glove and you've got the stuff on your skin. With thousands of patients and hundreds of workers under less than ideal conditions, some of the care takers get exposed directly or indirectly.
By mobility, I mean humans can move into dramatically different environments, and from isolated regions to dense population centers.
Re the pigs — I couldn't find any reference to Ebola research in warthogs. Who is doing those experiments? I know they've found bush antelope and porcupines (which are not related to pigs) with Ebola.
Re domestic pigs. I never really thought about it either. There are many pig farms in Southern Africa. I have never been to Liberia, Guinea or Sierra Leone so I haven't a clue about pigs there. I've been to Senegal (where I doubt there are pig farms) and Nigeria, of course, has pig farms, but there isn't really an outbreak there yet. Pigs are being promoted in Africa by development people as good/profitable small farm livestock — perhaps it is best not to unfairly label them as a vector of disease.
And I'm still not convinced that humans aren't more like pigs than small non-human primates — especially when you throw co-factors/other respiratory conditions in.
But here is another question. Do you think the R0 for ZEBOV could be changing?
Nobody has looked at warthogs, and there is no really good reason to do so, as they live in a very different habitat.
To my knowledge, the animals that have been found "with ebola" that are not fruit bats are found sick/dead. Among fruit bats, there are various indicators of Ebola association (like evidence that the animal had Ebola, or actual Ebola RNA, etc.) Several species of fruit bat show that.
I'm not sure how accurately R0 is measured for a disease that has emerged only a handful of times. The estimates I've seen range across almost an order of magnitude, reflecting this uncertainty.
I am not a scientist, therefore will never be qualified to comment in any way scientifically on this post. Tonight my 15 year ond son came in from school and said Dad - I am going to get some filter masks.
This is a worry for him - and I cannot do anything to help him. But Greg Laden's words have poured oil upon the waters for him. Thank God for men like Greg - who give people more understanding and more recognition of what they may be likely to be confronted with. Thank you Greg for answering all of the cranks and nuts with logical argument. Thank you for being here for us and thank you - for sharing your knowledge
Elsdon Ward
Let us keep in mind that the Flu was not identified to be truly airborne until the last few years. It was thought to spread through large droplets for decades. The flu is a common disease, and modern medicine has literally dealt with billions of flu patients for a long long time. By contrast Ebola is a poorly understood virus, with limited human to human transmission ever observed. It is accurate to say that we have seen more human Ebola transmission in the last 6 months, than we have in the rest of medical history...
Ebola is present in Saliva, and can enter through mucous membranes of the eyes, nose and mouth. It infects a variety of cells, including epithelial cells, which line the throat, and upper airway.
Various strains of Ebola have been effectively aerosolized in the lab, and both Ebola Reston, and Marburg are believed to be airborne filoviruses, therefor there is obviously no structural limitation preventing them from becoming airborne particles.
I have conferred with more than one medical doctor, epidemiologist, and virologist, and collectively they have been unable to provide a single definitive reason that Ebola Zaire couldn't become airborne, or couldn't in fact BE airborne. They could only say airborne transmission had not been observed, and that there was no solid scientific evidence that it was currently occurring. That said there IS limited anecdotal evidence that this kind of spread might be occurring.
Thanks for this Greg Laden and for the discussion in the comments (& on your blog generally) too. Interesting and informative and appreciated.
From Greg Laden #24 : It is an Asian virus, like Ebola but not the same thing. It is not a form of Ebola, but a related disease.
Okay. That was the exact thing I was going to ask about (#23 Mark beat me to it.) but I am confused by this. I thought Reston was a strain (variety?) of ebola along with the Sudan and Zaire/ Congo strains - admittedly based mostly on reading Preston's 'The Hot Zone' book - but you're saying it is actually a different disease altogether? That's news to me although I'm very happy if I'm wrong here! Can you elaborate on that a bit please?
Also sad to hear about your neighbor, Patrick and the others affected. My condolences to his family and friends and to those of all those affected by this horrible disease. I suppose its trite to note that this virus has claimed too many human lives and caused too much suffering and torment already but I'll say that anyhow. Just hope the experimental vaccine mentioned on this blogeralier is effective and gets used and cures this ASAP.
Tonight in Australia we've just had news of a possible case with a Cairns based health worker from an African ebola clinic having blood tests after having a low grade fever. It'll probably turn out to be nothing, something else a scare, like the last one here in Oz but we don't know yet. I think the fear of a global pandemic that'll kill us all is over the top -Occam's razor and the least dramatic possibility being the likeliest thing and all. But still. Glad for this reassuring article - expect and sure hope Greg's right.
PS. FWIW. I would've said Uganda was Central Africa, Congo West Africa and Sudan East Africa but that's a whole other and not at all significant issue.
PPS. How do you think the Spanish nurse was infected and what do you think of them euthanising her seemingly unrelated pet dog? Did you hear about that?
@ ^ See :
http://www.slate.com/blogs/the_slatest/2014/10/07/spain_will_euthanize_…
Plus see :
http://www.abc.net.au/news/2014-10-09/ebola-scare-woman-under-observati…
Plus :
http://en.wikipedia.org/wiki/The_Hot_Zone
Which was my first and most memorable source for info on the filovirii. Have you read that Greg Laden & if so what did you think of it - is it pretty much right or too dramatised?
For the record, I reckon putting down the Spanish nurse's dog was cruel and unnecessary and shouldn't have happened. Think they should've tested it for ebola and maybe quarantined and checked it but not just killed it. Pets are family where I'm concerned.
But I'm no expert - well on ebola &disease control anyhow - so could be wrong. Seems bloody rough on the dog & nurse alike though.
I read the Hot Zone a long time ago and I remember it being a bit dramatized. But my main memory is this: At about the same time I read four or five books written by infectious disease people, and discovered that there were strong internal rivalries in that profession, though you wouldn't know it from reading one book. They give different stories and to some extent one writer will leave out the other writer from the story totally even though they were both there. I found that interesting.
If you take those early Hot Zoneesque books and compare them to higher quality long form journalism of today, they were crap. Things have actually improved.
Laurie Garrett's The Coming Plague is, at least, based on scholarly work (it's her PhD thesis, essentially). That's good. Dated, but now an important historical document (no offense, Laurie... all of our theses become important historical documents!)
Link to an entertaining tweet on this subject:
"I wonder if all the conservatives yelling that Ebola might become airborne realize it means they now believe in evolution?" -- Charles Johnson
@66. Greg Laden : Okay. thanks illhave tosee if ican find a copy of that
.. Annnd of course, now I spot this :
http://scienceblogs.com/gregladen/2014/10/08/can-dogs-transmit-ebola/
Which I probably should've seen earlier -came here via a link, guess I should've refreshed and checked the blog page first. D'oh! Mea culpa.
Typos. Sigh. That's "I'll have to see if I can find a copy" natch.
BTW. Seems I was correct in one thing (if only one!) last night. turns out the Australian nurse has tested negative and does NOT have ebola :
http://www.abc.net.au/news/2014-10-10/cairns-nurse-tests-negative-for-d…
which is some good news on this issue for a change.
Vet Pathol. 2013 May;50(3):514-29. doi: 10.1177/0300985812469636. Epub 2012 Dec 23.
Pathology of experimental aerosol Zaire ebolavirus infection in rhesus macaques.
Twenhafel NA1, Mattix ME, Johnson JC, Robinson CG, Pratt WD, Cashman KA, Wahl-Jensen V, Terry C, Olinger GG, Hensley LE,Honko AN.
Author information
Abstract
There is limited knowledge of the pathogenesis of human ebolavirus infections and no reported human cases acquired by the aerosol route. There is a threat of ebolavirus as an aerosolized biological weapon, and this study evaluated the pathogenesis of aerosol infection in 18 rhesus macaques. Important and unique findings include early infection of the respiratory lymphoid tissues, early fibrin deposition in the splenic white pulp, and perivasculitis and vasculitis in superficial dermal blood vessels of haired skin with rash. Initial infection occurred in the respiratory lymphoid tissues, fibroblastic reticular cells, dendritic cells, alveolar macrophages, and blood monocytes. Virus spread to regional lymph nodes, where significant viral replication occurred. Virus secondarily infected many additional blood monocytes and spread from the respiratory tissues to multiple organs, including the liver and spleen. Viremia, increased temperature, lymphocytopenia, neutrophilia, thrombocytopenia, and increased alanine aminotransferase, aspartate aminotransferase, γ-glutamyl transpeptidase, total bilirubin, serum urea nitrogen, creatinine, and hypoalbuminemia were measurable mid to late infection. Infection progressed rapidly with whole-body destruction of lymphoid tissues, hepatic necrosis, vasculitis, hemorrhage, and extravascular fibrin accumulation. Hypothermia and thrombocytopenia were noted in late stages with the development of disseminated intravascular coagulation and shock. This study provides unprecedented insight into pathogenesis of human aerosol Zaire ebolavirus infection and suggests development of a medical countermeasure to aerosol infection will be a great challenge due to massive early infection of respiratory lymphoid tissues. Rhesus macaques may be used as a model of aerosol infection that will allow the development of lifesaving medical countermeasures under the Food and Drug Administration's animal rule.
Dianed: Context for this paper. First, the Soviets and the Americans probably tried to weaponize Ebola by making it airborne and were unable to do so do. They probably had limited time and resources, but the point is, it failed. Airborne has a certain definition and part of that is the species to which it applies. Kennel cough is airborne but human can't get or transmit it. Only dogs. Anyway, thanks for the abstrct.
If ebola is not airborne then please explain to me how a medical personnel can wear all of the proper PPO gear and STILL manage to get it. It can be transmitted through cough, and or sneeze which means it is airborne. This horrid disease is NOT strictly gotten by contact...if that is the case then the medical personnel are not wearing their proper PPO gear...and I know that if I still worked in the medical field and was in fear of a patient having it...I would be doubling the gown, doubling the gloves and wearing the mask the hospital made especially for me when I first started there. This crap IS airborne as well as contact given.
No it is not. That does not mean it isn't highly infectious.
The Center for Infectious Disease Research and Policy (CIDRAP; "SID-wrap") is a global leader in addressing public health preparedness and emerging infectious disease response. Founded in 2001, CIDRAP is part of the Academic Health Center at the University of Minnesota.....
‘We believe there is scientific and epidemiologic evidence that Ebola virus has the potential to be transmitted via infectious aerosol particles both near and at a distance from infected patients, which means that healthcare workers should be wearing respirators, not facemasks.”
Adequate protection is essential
To summarize, for the following reasons we believe that Ebola could be an opportunistic aerosol-transmissible disease requiring adequate respiratory protection:
•Patients and procedures generate aerosols, and Ebola virus remains viable in aerosols for up to 90 minutes.
•All sizes of aerosol particles are easily inhaled both near to and far from the patient.
•Crowding, limited air exchange, and close interactions with patients all contribute to the probability that healthcare workers will be exposed to high concentrations of very toxic infectious aerosols.
•Ebola targets immune response cells found in all epithelial tissues, including in the respiratory and gastrointestinal system.
Experimental data support aerosols as a mode of disease transmission in non-human primates.
Full article here.. http://www.zerohedge.com/news/2014-10-13/cidrap-we-believe-there-scient…
...
At this point Greg, it will be the public's perception of whether or not the virus is spread through the air that will have an irreversible impact on the outcome. The public does not trust what they are being told by the CDC. I can tell you from experience that ICU staff members must consider their own families when determining the dangers involved in caring for someone with an infectious disease. If these professionals believe the protection they are offered is not adequate... or that the risks are far too great...who will you find to isolate the patients? The infected population will overflow back into the general population and the consequences will be immense. It is my belief that Ebola should be treated as an airborne viral infection at this point for that reason.
DIaned, I'm familiar with the original report. I disagree with saying Ebola is airborne based on this.
The UMN researchers make two points that I agree with pretty much .First, they ask for brining the definition and discussion of "airborne" and aerosol etc etc. more into the modern age, pointing out that the modern nomenclature etc. is based on pre-knowledge considerations (knowledge of what is happening i water droplets, etc) and is arcane. I tried to infuse that into the current conversation several posts back but it was too difficult, but it should be done. Second, they are recommending respirators. I do not know if short distance "through the air but not airborne" transmission is happening though breathing. Aerosol is not just the kooties fly through the air, but that they are transferred via the respiratory system of the new host. That is incredibly important. But, your body is your body, including your mouth and the inside of your nose and you breath. Every breath in is an invitation to whatever is out there. A mask may not be enough. Respirators would be nice.
I think they should deploy respirators in one region where the outbreak is right away at whatever cost and see if it makes a difference. They could start at a hot zone and spread the use from there over time, so eventually everyone gets them. But there would be a record an that would allow a wedge of time/space change i use which would allow a quick check to see if it matters.
But, ebola is not airborne.
Plant virus jumps to Honey Bees
http://www.eurekalert.org/pub_releases/2014-01/asfm-ppv011714.php
SparrowShadow: I hate when that happens!
The premise of this whole discussion ignores one possibility, natural adaptivity is not engineered.
marryk: What do you mean?
Ebola already has been airborne 25 years ago in 1989 in Reston Virginia which is how the Ebola strain Reston Ebola got it's name. Granted it didn't show that it could harm humans and only monkeys at that time, but this PROVES that Ebola as with any disease can evolve and in fact become an airborne contagion. Assuming otherwise is absurd.
Sandman, Reston is an Asian virus. It is like Ebola (many call it a form of Ebola) but it may have a totally different ecology and certainly has a totally different history. It is not a human disease.
It's kind of scary how this guy who seems so sure about what he is saying, uses words like diseases "in general", "but they really don't change their mode of transportation"(tells me that they could),"I'm pretty sure", "this does not happen very often", "we expect..." (who is "we"?), "probably", "IF it did..."(if and it may or may not??), "the chances are" (oh, so there is a chance), "potentially", "rarely", "may or may not", "except possibly one". well, I'm real convinced now! the only absolute facts are that us humans are not in control, we don't know everything nor will we, we are not Omni-powerful, etc. but one thing for sure is God is, so put your trust in Him and not in the arm of the flesh. let me end this by saying I thank God for doctors (I go to them), and dentists and cancer research and vitamins and stitches and band aids and surgery and blood transfusions and God using people to save other people from ebola. my point is, we just can't think we know it all when it comes to ebola and other viruses. if we did, this guy wouldn't have used all those words.
Noreen, let me know how that goes for you. I'm sticking with the science. And yes, science is not certainty. Only faith provides perfect certainty. For what it is worth.
The other day, on a NEJM webinar, an MSF doctor pointed out that if Ebola were airborne, there would be more evidence of unlinked transmission — cases that did not have close contact with other cases. And that evidence has not been seen — with the possible exception of some of the nosocomial infections. But those could have been due to droplet transmission, or quite frankly, accidents. BTW, the CDC issued this fact sheet that makes a clear distinction between airborne and droplet spread: http://www.cdc.gov/vhf/ebola/pdf/infections-spread-by-air-or-droplets.p…
A hypothetical - I wonder if tomorrow the Directors of Health in Sierra Leone, Liberia and other West African countries were offered a 100% effective, proven vaccine (or even another 100% effective preventive strategy) against malaria or one against Ebola which would they choose - and which one would the donors give funding towards an "EPI type" program if they had to choose.
Malaria, hands down.
HIV, HCV, polio all undergo recombination during replication.
Why not ebola?
Ag shift is reASSORTMENT in flu, so yes, this is very different process.
Rather than focusing on airborne spread... it's probably a greater likelihood that a mutation creates a virus that makes it attenuated slightly... increasing chance of spread before people get really sick. All depends on how long this outbreak goes on.
Chris, I actually didn't use the term recombination, or reassortment, in the post, but you are right, there is a difference, and I added a word to clarify.
The viruses you mention have changed in the wild through recombination. But given the widespread nature of HIV, for example, it is interesting to not that it has not changed much, not at all in its mode of transmission. That supports, rather than refutes, the argument.
Also, again, the genetic source of West African Ebola is still a single individual. HIV probably existed for decades before it became a pandemic (see: http://scienceblogs.com/gregladen/2014/10/27/ebola-and-the-french-disea…) The time scales (a year vs. something approaching a century) are vastly different. And, again, HIV has not changed its mode of transmission.
But yes, the possibility that Ebola changes in a way that makes its spread more likely because of differences in the link between symptoms and the ability spread is a concern. But, since its current mode of spread is closely related to symptoms, it may not amount to much. I would worry a a lot more if it was already airborne and became more focused in that modality.