It can't be said often enough that "nothing in biology makes sense except in the light of evolution." Moving from physical characteristics--color, bone shape, the form of bacterial cells--to genetic characteristics in order to classify organisms--and infer phylogenies--was a giant advance. That the molecular characteristics confirmed what was known using physical characteristics was a breakthrough, and allowed for more sophisticated analyses of organisms that don't have bones or other easily-observable physical features that allow for simple classification into groups: microbes. I've previously pointed out the utility of phylogenetic analysis in tracking the spread of pathogens. A new study on the origin and evolution of HIV employs a similar approach in order to elucidate the history of the virus in Africa.
It's been known for over 15 years that viruses related to HIV type 1 (the most common type; a nice overview of different types and strains of HIV can be found here) could be found in non-human primates. This related virus is called the simian immunodeficiency virus (SIV). Like HIV, there are a number of different strains of SIV; the type that was previously detected in chimpanzees is therefore designated SIVcpz, to show it's from chimps (or even more specifically, SIVcpzPtt for isolates that come from the chimpanzee species Pan troglodytes troglodytes.)
The virus hadn't, however, been studied previously in chimps out in the wild, for a number of reasons. These chimps are endangered and reclusive, and live in remote areas where they are difficult to study. Therefore, our knowledge of SIVcpz in chimpanzees comes from studies done in captive animals. A combination of new methods has allowed researchers to track the virus in wild chimps in the west central African nation of Cameroon.
I mentioned how much you can learn from, well, animal shit. That's exactly what this study boils down to. Researchers collected almost 600 fecal samples from 10 sites in southern Cameroon. From these, they did three tests. One, they extracted DNA in order to examine the mitochondrial DNA of the chimp who'd been kind enough to provide the fecal sample. From this, it was found that 423 of them were the same subspecies: Pan troglodytes troglodytes. All samples were then tested for HIV-1 antibodies; 34 samples were positive, all from P. t. troglodytes. These antibody-positive samples were further examined using the polymerase chain reaction (PCR) to amplify viral genes. Additionally, they were able to examine portions in the chimp DNA that allowed them to distinguish individuals (so that it could be determined how many different chimps were represented by the positive fecal samples). They found they came from 16 different chimps--7 males, 9 females.
But all this was just the beginning. They then analyzed the genetic sequences of these 16 new viruses they collected and compared them to previously-identified viruses. They carried out these phylogenetic analyses using both individual genes as well as the entire viral sequences. A few key findings emerged from this. First, the viruses generally grouped according to geography: viruses which came from chimps geographically close together were more similar than those from chimps separated by physical distance, or barriers (such as rivers).
Second, in regard to the origin of HIV, this study also found viruses more closely related to HIV-1 than those previously identified. Indeed, SIVcpz strains from two sites--designated MB/LB in the very south eastern part of the country, and EK, in south central Cameroon--were more closely related to viruses in HIV-1 group M (the most common HIV-1 group) and N (a rare group), respectively, than they were to other isolates of SIVcpz. (See figures 3 and 4 of the paper). The group has carried out further studies in these areas with similar findings, and therefore conclude that chimps in these areas of Cameroon are the sources of these groups of HIV-1.
However, Cameroon doesn't appear to be the origin of the human pandemic. This may seem contradictory, so let me explain. Other studies (such as this Journal of Virology paper) have shown a high diversity among HIV-1 isolates in the Democratic Republic of Congo, suggesting many, many years of evolution and diversification of the virus in that area. This fits with what we know about the history of the virus as well. The first retrospectively-identified case of AIDS is from 1959 in Kinshasa, DRC. So while Cameroon is suggested as the place where the species jump occurred (and there may have been limited local transmission), the epidemic really began when it was carried to the bigger city of Kinshasa and spread there.
The research also suggests multiple transmission events of SIV into the human population. I mentioned previously how butchering or consumption of bush meat is one way animal viruses can be transferred to man. We cannot be certain this is what happened with the transmission of SIV into the human population, but it is one potential route. Indeed, as independent transmission events seem to have occurred for HIV-1 groups M, N, and O, they could each have had different transmission modes into the human population.
Additionally, this phylogenetic analysis has been used to track the origin of SIVcpz itself. It appears that this virus is a recombinant of SIVs that infected other species of monkeys in West Africa: red-capped mangabeys and Cercopithecus species. Chimps are known to be hunters and will kill and eat other monkeys, so it's possible that they, too, became infected due to their hunting and eating practices. Whether that recombination event occurred within chimps or prior to their infection with the virus isn't currently known, but it again shows just how much we can glean from analysis of the genetic sequence of these pathogens.
Finally, this research isn't the first to point to chimpanzees, and Cameroon, as the source of HIV-1. Previous studies of SIVs in captive but wild-caught chimpanzees from that country (for example, this study) showed high similarity to the human virus. Other evidence for a chimpanzee/Cameroon link is reviewed in this Science article. And transmission of SIVs (or other primate viruses) to man appears to be a regular occurrence. A study published in PNAS this time last year showed that cross-species transmission of viruses from primates to bushmeat hunters is an ongoing event. Since it appears SIV transmission into the human population has occurred on multiple occasions (leading to the M, N, and O groups of HIV), we have no reason to think it's not an ongoing process, and that nature may have something worse to offer than HIV. It also, of course, has implications for current surveillance of H5N1. No one knows how many times in history SIVs have entered the human population, only to meet a dead end in the infected human (as H5N1 generally has to date). As this study shows, it only takes one successful transmission event to lead to a pandemic.
References
Hahn et al. 2000. AIDS as a Zoonosis: Scientific and Public Health Implications. Science. 287:607-614. Link.
Keele et al. 2006. Chimpanzee Reservoirs of Pandemic and Nonpandemic HIV-1. Science. [Epub] Link.
Vidal et al. 2000. Unprecedented Degree of Human Immunodeficiency Virus Type 1 (HIV-1) Group M Genetic Diversity in the Democratic Republic of Congo Suggests that the HIV-1 Pandemic Originated in Central Africa. 74:10498-507. Link.
Wolfe et al. 2005. Emergence of unique primate T-lymphotropic viruses among central African bushmeat hunters. PNAS. 102:7994-9. Link.
Zhu et al. 1998. An African HIV-1 sequence from 1959 and implications for the origin of the epidemic. Nature. 391:594-7. Link.
Additional information: Christine Gorman at the TIME Global Health blog has a story on the paper as well, and an interview with study author Beatrice Hahn here.
Image from http://i.a.cnn.net/cnn/2006/WORLD/africa/05/25/chimps.AIDS.reut/story.C…
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Tara,
Great summary. I'm sure that when you refer to chimps eating "other monkeys" you're aware that chimps are apes, not monkeys.
Second GT's comments. Tara, you're letting me down. I'm quite disappointed. *insert obligatory chastisement here*
Cladist in the house to set these fools straight. Monkeys are a paraphyletic taxon made up of old world monkeys (OWM) and new world monkeys (NWM). Higher primates can be divided into OWM, NWM, and apes. Apes and OWM are the closest relatives, and NWM are the outgroup (ie, apes and OWM share a more recent common ancestor than aps/OWM and NWM).
For those familiar with phylogenetic shorthand, the relationship of the three taxa are:
((OWM,Apes),(NWM))
For a cladist, OWM, NWM, and apes are all just monkeys. The proper phrasing would be "Chimps eat OWM" (NWM live in the new world, and chimps live in africa). I see nothing wrong with saying, "chimps eat other monkeys."
Cladist, out.
In the English language, "monkey" can be used to refer to apes. Obviously it's less specific, but no less correct. Saying otherwise is prescriptivism and contrary to how languages evolve. The cladistic perspective is interesting but ultimately irrelevant; all that matters is how the word is used and understood by others.
It is so odd to me that science-minded people often take such an unscientific approach to language, insisting that one usage or another is correct and all others incorrect. It's kind of like saying that one particular mutation is correct and the rest are wrong, and if they happen anyway, evolution must've erred.
((((((Pan,Homo)Gorilla)Asian apes)OWM),NWM))
I hope RPM has no problems with referring to his/her spouse as a monkey.
Back to Tara's analysis. I think one of the lessons from this history of AIDs is the danger posed by the eating of bushmeat. What other viruses are prepared to make the jump to man?
Apparently the one that kills the sense of humor already has....
And incidentally, when discussing paraphyletic classification, (the way I understand it) it would still be appropriate to distinguish apes from monkeys since a paraphyletic designation does not have to contain all the descendents of the most recent common ancestor. Much like excluding Aves from Reptiles.
It's a bit off topic but I'm currently working on some methods to estimate epidemiologic parameters such as the probability of transmission at each stage of HIV infection and the rate of sexual mixing in (empirically or a priori) defined risk groups directly from phylogenies of HIV from human cases. I think that the role of phylogenetics in transmission system science and public health is undergoing a rapid and well-needed expansion. Thanks for the post.
Tara
I have no idea if you have ever addressed this, and it kind of fits here but not really. When people move to another place often psychosocial factors are blamed for them getting diseases that they don't usually get, or being sicker than usual. Could this have a different cause- like certain people who live in an area are used to the bugs, and the people who move in are not so it affects them more?
If I'm reading the paper correctly, I don't think we can conclude that Cameroon is necessarily the site of the original jump from chimp to human. The range of P. troglodytes troglodytes runs along the Congo River for a considerable distance upstream of the site that the first human case was identified. The Congo River historically has been a major "highway" with much human movement up and down stream. Two of the SIVcpz strains that most closely resemble human HIV1 were found in extreme southeastern Cameroon, the point where the study area is closest to the Congo River. I think it is reasonable to conclude that chimps just to the southeast of MB and LB, outside the study area, could also harbor similar SIV strains. Those chimps weren't assayed in this new study, and previous studies presumbly didn't use this sensitive new technique. Heck, the relevant populations might even be extinct by now.
Whether the disease arose along the Congo, or in Cameroon and then migrated down the Sangha to Congo as the authors of this study suggest, I'm inclined to favor the "Heart of Darkness" hypothesis to explain its subsequent spread: Chimp to human transfer of SIVcpz has probably occurred frequently in the range of P troglodytes troglodytes without getting much of a toehold in the human population. In the early 20th century, the brutal oppression of the Congolese population by Belgium produced widespread social disruption (including migration, prostitution, etc) and a great many stressed, malnourished people with depressed immune systems. Combine that with the widespread use of injectible medicines and probably less than perfect sterilization of needles, and you have a perfect storm for the mutation and spread of a new virus.
Ah, y'all are so picky. :) Thanks for the defense, RPM. I suppose I could have left out the word "other" but I didn't even think about it when proofing.
We really don't know. The other PNAS paper I linked mentioned another type of retrovirus, but it could be anything. Each species likely carries some of their own specific viruses, and we just don't know enough about the micro-ecology of individual species to say which ones may be most likely to adapt to man upon exposure. We generally only find them retrospectively, after something like HIV (or SARS, or H5N1, or hantavirus, etc.) has been found in man.
I'm not sure what you're considering as "psychosocial factors" here. Often when people move or travel, they get new diseases because the people who've lived there are already immune, and the new folks aren't. Could this be the case with HIV? IMO, unlikely. We don't have evidence that this virus has been circulating in the human population in Africa for longer than the past ~80 years, and we don't have any evidence that folks in the area investigated in this study were more likely to be resistant or immune to the virus than folks in, say, DRC.
True, but the abstract I linked adds a bit more data (and 700 additional fecal samples) and confirms a Cameroonian location. But you're right--we're far removed from the original jump, and both the chimp populations and the virus have changed a bit over time. It's impossible to definitively say "the virus jumped here," but the data point to Cameroon.
I wonder if there is reason to suppose that "butchering or consumption of bush meat" led to interspecies transmission rather than the obvious route of sexual contact.
True, but the abstract I linked adds a bit more data (and 700 additional fecal samples) and confirms a Cameroonian location.
Hmm, yes, but again the samples were all collected in Cameroon and nowhere else. The authors say that their studies are the first of this kind to look at wild chimpanzees, so it seems that for the pandemic HIV-1 Group M, we have a strong link to the southeastern corner of Cameroon and "no data" for the adjacent regions of Congo. I think it's worth noting that the MB and LB sites are at the edge of the study area and could easily represent the northwestern border of a larger range for those particular SIVcpz strains.
A Cameroonian origin seems fairly well supported for HIV Group N, but since that strain of HIV has only been found in Cameroon, it's not exactly a surprising result.
To support a Cameroonian origin for HIV Group M, we would need data from chimpanzee populations located between LB/MB and the Congo River. If those populations are negative for the relevant SIVcpz strains, then (and only then) can we conclude that Cameroon is the source of HIV-1 group M. Since there are geographic, epidemiological, and sociopolitical reasons for suspecting that the AIDS pandemic originated along the Congo River, I think that it is premature to point to Cameroon as the origin of Group M.
"Obvious?" Sexual contact with animals is something you consider more ordinary than hunting and eating them?
Man... I suppose we don't want to know details about your lifestyle, do we?
Tara
Thanks!
The psychosocial factors are things like adjusting to a new country, moving from rural to urban and customs and foods and distance from relatives. The comment that twigged the question was: First, the viruses generally grouped according to geography: viruses which came from chimps geographically close together were more similar than those from chimps separated by physical distance, or barriers (such as rivers).
This led me to think that introducing a new person to a new bunch of bugs in a different area would cause more serious illness in the person that is coming new than someone who is native, if bugs are sort of (I don't know if this is right) a certain way in a certain area.
Kind of like the reverse of smallpox coming into a native population - the native population is going into the smallpox. Does that make sense?
I just question the psychosocial models of disease usurping a more scientific explanation.
Could a big city have different and more/less virulent bugs in certain areas? How far away or sheltered does one have to be in order to be introduced to a "new" bug? I am probably saying it wrong, but can a major urban centre have bugs that are specific to certain areas?
Ah, yes... It's sentences such as this one that set the tone of the article:
"Chimps are known to be hunters and will kill and eat other monkeys, so it's possible that they, too, became infected due to their hunting and eating practices."
Hm, "it's possible"... That may make it a good bedtime story for your kids, but where did science go?
Great conversation for the kids, too: "What does your dad do?" - "He's looking for ape shit in Africa."
What do we need this fiction for? Do we really have to believe that the virus came out of Africa, just to infect the gay community in N.Y.C. and S.F., while it proved unable to make even one monkey sick there, after which it went back again to Africa to infect the whole populace?
Monkeys are full of viruses, but none of them bother them much. But I can reveal the origin of all these monkey stories: Once upon a time there was a virologist named Robert Gallo. He was not a very good virologist, because he had weird ideas, like searching for a virus that causes cancer. But one day he stumbled upon a virus preparation that he called HL23, which he presented proudly as the first human leukemia virus. But most of the virologists of that time were rather skeptical. They showed that the "HL23" virus actually consisted of no less than 3 (!) monkey viruses. The reason? Viruses are frequently grown in cultures of monkey kidney cells. That is the origin of the connection between virtual human viruses and real monkey viruses. And Gallo? He finally got famous for the invention of a virus that was rumored to cause a disease that was specially invented for this purpose. And he lived happily in clover ever after.
That is science. It's called a "hypothesis."
Of course, that's not even close to the scenario suggested.
**Do we really have to believe that the virus came out of Africa, just to infect the gay community in N.Y.C. and S.F., while it proved unable to make even one monkey sick there, after which it went back again to Africa to infect the whole populace?
*Of course, that's not even close to the scenario suggested.
That IS the prevailing paradigm, believed by hundreds of millions of people the world over. *Somehow* you and your friends are going to connect the dots for us: from monkeys in Africa to gay Canadian airline stewards ("patient zero"), to a handful of men in L.A. in 1980, to San Francisco to New York City, then back to Africa to infect millions. It's been 25 years, can't you guys get your ducks in a row in regard to this mythology?
Surely you know that the appeal to popularity is a logical fallacy. Just because "hundreds of millions of people" believe something doesn't necessarily make it so.
Thing is, it never had to go "back" to Africa--it never left. That's always been the epicenter--it spread out from there after smoldering for many years. You mention mythology, yet you spread it by naming "patient zero," which was overplayed to the point of mythology. Even if he did contribute to the spread of the epidemic, the virus was already circulating outside of Africa by that point, and spreading within that continent as well. Your explanation suggests a straight line of spread, but it wasn't. Think of it more like a pool of water you throw a stone into--it radiates out. It simply wasn't recognized until it got into a population unique enough that health officials could say, "there's a strange pattern forming here...we need to check this out."
"Surely you know that the appeal to popularity is a logical fallacy. Just because "hundreds of millions of people" believe something doesn't necessarily make it so."
I absolutely agree. What I'm saying is this the story the media have been peddling for 20+ years. Is it any wonder that so many people accept it as truth?
So when are you and your colleagues going to set the record straight? When are you going to connect the dots for all of us lesser mortals? Isn't this what you do?
"Surely you know that the appeal to popularity is a logical fallacy. Just because "hundreds of millions of people" believe something doesn't necessarily make it so."
You couldn't have said it any better, Dr. Tara. Just because hundreds of millions of people believe HIV causes AIDS, doesn't necessarily make it so. Thank you.
Who in "the media" has been saying that HIV went "...from monkeys in Africa to gay Canadian airline stewards ("patient zero"), to a handful of men in L.A. in 1980, to San Francisco to New York City, then back to Africa to infect millions" ?
Avert.org has a very straightforward page on it that says nothing of the sort, and certainly I didn't suggest any of that above.
And I agree with that--it doesn't make it so. The evidence, however, isn't popular opinion, and the evidence does definitively point to HIV as the cause of AIDS.
"The evidence, however, isn't popular opinion, and the evidence does definitively point to HIV as the cause of AIDS."
Two examples of the "evidence" being popular opinion...
first, the "Durban Declaration". The only time I've ever heard scientists coming together to state an hypothesis as fact, in an attempt to refute critics.
second, the fact that Gallo found "HIV" in only one-third of his AIDS patients, and that awkward fact somehow continues to survive scrutiny and become the mythology we all know and love.
So when are you and your colleagues going to set the record straight? When are you going to connect the dots for all of us lesser mortals? Isn't this what you do?
I'm still waiting...and so is the whole world.
That's not evidence. It's a document summarizing the evidence that HIV causes AIDS, and showing the massive support of the hypothesis on behalf of the scientific and medical community, but it's not the evidence itself.
Funny how all HIV deniers seem to think the research started and ended with Gallo. If no other studies had confirmed his findings, do you really think HIV would still be touted as the cause of AIDS? Plenty of other scientists that were more respected than Gallo have been proven wrong in their careers, and from the personality conflicts I understand swirl around Gallo, I'm sure he has plenty of people who'd like to knock him down a notch. And yet thousands of studies have confirmed HIV as the cause of AIDS. That's not an appeal to popularity; it's just the way science works.
"Funny how all HIV deniers seem to think the research started and ended with Gallo.'
Funny how when Gallo's incredibly flawed research is mentioned that the faithful quickly abandon Dr. Gallo.
"And yet thousands of studies have confirmed HIV as the cause of AIDS. That's not an appeal to popularity; it's just the way science works."
It IS an appeal to popularity, a blatant one.
Now, did those thousand of studies begin by questioning whether HIV causes AIDS, or did they work under the assumption that HIV causes AIDS? There's a distinction there, that I'm sure you can appreciate.
You see, if the hypothesis is flawed at it's base (Gallo's research), and you do all your work from that flawed base, then you'll simply expand that flaw exponentially.
Can you please answer these questions? The world has been waiting twenty five years...
So when are you and your colleagues going to set the record straight? When are you going to connect the dots for all of us lesser mortals? Isn't this what you do?
Interesting how another parallel between evolution denial and HIV denial emerges. You set up scientists as a church with Gallo as their deity, as evolution deniers accuse scientists of a similar "faith" with Darwin at the head of the table. What neither of you seem to realize is that there's science beyond Gallo and Darwin.
There has been both. In the early years, of course it was questioned, and extensively so. Gallo's studies needed to be--and were--replicated by other labs. Now that this as been replicated many, many times, it's of course the starting point of new studies that HIV causes AIDS, just as we also assume Mycobacterium tuberculosis causes TB, and Streptococcus pyogenes causes strep throat. Do you chide scientists for making those assumptions as well?
"Gallo's studies needed to be--and were--replicated by other labs."
It's obvious then that others have no trouble duplicating Gallo's flaws. But thank you for agreeing that Gallo's research is the foundation of this hypothesis.
Dan,
You know you got Doc Smith on the ropes when she does 2 things:
1. Vaguely mentions the "thousands of studies have confirmed HIV as the cause of AIDS" ---without citing an actual study
2. Injects ID or strep throat to the discussion -- her 2 default opinions.
Well done!!!
HankBarnes
Oh, indeed, he sure has me. He even got me to admit that the HIV hypothesis can be traced back to Gallo (among others, of course). What a crafty bloke that Dan is to get me to make that startling admission.
And Hank, I see you ignored the 4 studies alone on the emergence and evolution of HIV that I cited in the post above. Don't suppose you'd actually surpise me and address the acutal content of a post for once?
"When are you going to connect the dots for all of us lesser mortals? Isn't this what you do?"
Unfortunately, it seems as if Dr. Smith will need to sit next to you, put the pen in your hand and guide your hand herself. But, it is very difficult to do this and hold your eyelids open at the same time and convince you that there are dots to connect.
In fact, this is not what she does. She points out interesting science and gives her opinion. I am sure she welcomes reasoned debate. Which can be fun. Your comments (and Hank's troll-ments) are just boring.
What I am curious about is, what science (published peer-reviewed science if you please) you or Hank are in agreement with? Maybe your top 2 or 3?
Mine would be, the Germ theory (microbes cause infectious diseases including AIDs), evolution (both micro and macro), and Space Aliens are NOT among us probing our nether regions, dissecting our cows and vandalizing our corn fields. (The last bit is meant to be facetious. I actually have not thoroughly investigated the literature on the subject).
D
And Hank, I see you ignored the 4 studies alone on the emergence and evolution of HIV that I cited in the post above
I didn't ignore them. I liked the one where they spent 7 years sifting thru apeshit -- to determine that HIV originated in Cameroon chimpanzees:)
I think Dr. Hahn said it nicely:
We're 25 years into this pandemic," Hahn said. "We don't have a cure. We don't have a vaccine. But we know where it came from. At least we can make a check mark on one of those."
Hank B
One of Tara's pearls of wisdom:
>"And yet thousands of studies have confirmed HIV as the cause of AIDS. That's not an appeal to popularity; it's just the way science works."
Well, I hope not that science works this way. But let's not be too demanding and ask to see these "thousands of studies". I'd be willing to settle for just one. Yes, that's reasonable, isn't it, Tara? Just show us one scientific paper that presents proof that HIV causes AIDS (or even that HIV exists). If you can do that, I'll even support your nomination for membership in the National Academy of Sciences. It's also a perfect opportunity for you to show up Kary Mullis, who was not able to find such a reference.
Yes, there are thousands of papers, even hundreds of thousands. I've read many of them (waste of time). Just read them carefully, and you'll see that, without exception, they base their conclusions on the basic assumption that HIV exists and causes AIDS. As if that were an unquestionable fact. And the material they work with? Oh, they just mindlessly assume again that the supernatant of that cell culture it is a pure preparation of "HIV". Why? Because they have sequenced whatever crap is in there. What standard do they compare these sequences to? Well, eh... nothing. It's HIV RNA, ya hear! That just IS so. You can't blame these chumps, because this (fully automated) sequencing technique is the only thing they know. Today's crop of virologists is so incompetent they would make the old pros cry. They just do what all the others do. Originality is completely foreign to them. And you can tell your colleagues that I said so.
Of course it's easy to duplicate the work of Gallo and Montagnier. Their original experiments were failures; neither one of them found any virus particles in a density gradient.
I don't have to explain to you what the difference is between correlation and causation. But even the correlation between the serological test (which is supposed to show HIV antibodies) and the AIDS-defining diseases was bad. So the CDC had to come up with a new name for "AIDS without HIV".
They call it "idiopathic CD4 lymphocytopenia". (yuk! yuk! yuk!)
So the CDC had to come up with a new name for "AIDS without HIV". They call it "idiopathic CD4 lymphocytopenia". (yuk! yuk! yuk!)
And ICL apparently represents something like 1% of all CD4 lymphocytopenia while ~ 90% of HIV positive individuals (who represent less than 1% of all Americans) go on to develop CD4 lymphocytopenia. I'm no mathematician but it seems to me the odds are much better being HIV seronegative.
Note that I'm not related to any medical field, but I really fail to see how you can substantiate the belief that HIV doesn't cause AIDs. Just statistically speaking, they obviously directy correlate. "second, the fact that Gallo found "HIV" in only one-third of his AIDS patients" Maybe the other two thirds didn't have AIDs at all, but a similar either misdiagnosed or unknown desease. After reading various articles on the subject, apparently those classified with ICL tend to not fit the usual profile for AIDs patients. How can you explain the fact that as AIDs incident rates go up, so do HIV rates. Not only that, but HIV rates tend to lag behind the AIDs rate by a few years...which makes sense as HIV patients are expected to live a few years before developing AIDs.