Naked Science Forum
Life Sciences => Cells, Microbes & Viruses => Topic started by: JennyDofat on 01/03/2004 19:38:32
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How soon after contracting HIV does ones immune system weaken?
Jennifer
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Variable depending on the state of health of the person in general and the state of health of their immune system. Most of the people will sero-convert, meaning you can detect it in their bloodwork, in six months.
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Nancy, does contracting HIV make acquiring AIDS a certainty ?
'Men are the same as women...just inside out !'
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Good question, and I'm not real sure of the answer. I would suppose, given enough time, that all people would develop AIDS, however, there have been cases of a positive result for HIV, which later turned negative. The last test I was familiar with was the ERISA test, which has, I thought, a pretty high error margin. Then again, some people stay HIV positive for years without ever developing AIDS. I think some of the babies born to HIV positive mothers are born HIV positive too, but some of them convert to negative after time.
A long time ago I attended a lecture at Tulane University, and the lecurer said that the AIDS virus actually mutates within the body about every two weeks, which was why they were having so much trouble getting rid of it. And your poor immune system has to reprogram every two weeks to recognize and attack the new mutant version. I guess it finally gets exhausted and you succomb and get AIDS. Maybe Chris could shed more light on that. I'm not an AIDS expert.
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I don't know that being HIV+ makes AIDS a certainty, but it's likely. HIV is such a pain because like all retroviruses, it integrates into your genome when it takes over the cell. I believe it behaves like some bacterial viruses in that it can pick up bits of your genome when it replicates, mutating the virus. The strain on the immune system (part of it anyway) is that it attacks helper T-cells, so the cells that are supposed to be killing it and preventing further infection are actually allowing it to reproduce further. Scary stuff.
There are several treatments given to people who are HIV+ to delay them from acquiring full blown AIDS. They involve inhibiting the replication of the virus by screwing with the enzymes it needs in various stages. (depending on the drug) The side effects are pretty bad though, from what I understand. Chris would know more about the pharmacology of these things.
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Speaking of retroviruses, read Darwin's (something can't remember) by Greg Bear, it's a fantastic book.
Am I dead? Am I alive? I'm both!
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Greg Bear has a couple of books in that series (that I know of). "Darwin's Children" and "Darwin's Radio".
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John - The Eternal Pessimist.
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I just bought Darwin's Radio (and a couple other Greg Bear books) a few months ago but haven't gotten around to reading it yet. Glad to hear some good reviews.
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Re: HIV and Immune system weakening.
Different people seem to have immune system weakening at different times after contracting the virus, eg 1-10 years. Some people get the AIDS defining illnesses before others and unfortunately die sooner. However with the modern drugs used to enhance the immune system in HIV infection people are living with the virus a lot longer and can survive for 15 to 20 years before getting the AIDS defining illnesses. Hope this is helpful.
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HIV (Human Immunodeficiency Virus) is the causative agent of AIDS (acquired immunodeficiency syndrome).
The virus was first identified in 1983 by Luc Montagnier and colleagues at the Pasteur Institute in Paris. In 1985, his team isolated the second human AIDS virus, HIV-2, from West African patients. American Robert Gallo is also credited as the co-discoverer.
The closest genetic relatives of HIV are a family of retroviruses called SIV (simian immunodeficiency virus), which are found in primates. One strain of SIV, SIVcpz, infects one species of chimpanzee (Pan troglodytes troglodytes) which lives in west central Africa. The SIVcpz strain carried by these chimps bears the closest genetic resemblance to HIV and is therefore viewed as the source of the human infection. Scientists suspect that at some time over the last 100 years the virus jumped from chimps to people and kick started the HIV epidemic.
How this species jump occurred has created a large amount of controversy. The theory which has probably attracted the most attention blames the experimental oral polio vaccine (OPV) which was being developed and tested in Congo (Central Africa, where HIV began) by American scientists from the Wistar Institute in the 1950's and 60's.
The argument put forward by proponents of the OPV-theory is that tissue and cells from locally-caught chimpanzees were used to make polio vaccines which were then administered to (a million or so) people in the region. If these chimpanzees were carrying SIVcpz (the probable genetic ancestor of HIV) then it is possible that it might have been a contaminant in the OPV stocks produced locally.
However, there are a number of problems with this theory. Firstly, we know how fast these viruses evolve or change genetically. By using this 'molecular clock' we can predict, on the basis of how different HIV now is from SIV, when the two viruses must have diverged i.e. when HIV began. On this basis, our current best estimates predict an origin for HIV sometime around 1930, plus or minus 10 years. This is 20 years too early for the polio vaccine trials.
Secondly, a 'fossil virus' was recently discovered (in 2000) in a sample from an African dating from 1959. The sample contains HIV and is currently acknowledged as the world's oldest reliable historical 'snapshot' of HIV from 40 years ago.
But this HIV is also very different from SIVcpz, indicating that by the time this strain of HIV infected the person who carried it, it had already evolved significantly since SIV jumped into people. It also 'fits in' in the right place on the evolutionary tree for a virus dating from about 1959 so it is viewed as a reliable specimen. Since the OPV trials were initiated at the time that this sample was taken, the origin of HIV must predate OPV because it would not have been possible for the virus in the sample to have evolved sufficiently rapidly within the time allowed.
This week researchers have been able to add one further, and possibly final, layer of evidence against the OPV theory. Because protagnosists of the OPV theory maintain that locally-caught chimpanzees were responsible for introducing the infection to man, scientists have visited the region of the Congo and analysed Chimpanzee faeces for traces of SIV. In a paper in this week's Nature Mike Worobey and colleagues announce that the local chimp population do carry SIV - but that it is a totally different strain of the virus to that which jumped into man. The version that caused HIV is carried by a different species of Chimp located over 1000 km to the west. This finding proves that locally-caught chimpanzees were not the origin of HIV in the Congo.
So how did HIV begin ? The most surprising fact is that SIV has probably jumped into people many times over. We know this is true because there is more than one type of HIV in circulation. The additional types represent independent jumps of SIV into people.
So why did none of these previous jumps become an epidemic ? The reason that it didn't become an epidemic is because it never spread far enough. The population were insufficiently mobile and local infections just fizzled out. It took Western doctors turning up in the early 1900's armed with syringes and needles and performing feats of vaccination like (according to one statistic) injecting 90,000 people with the same 6 syringes!
This kind of mass vaccination (against things like yellow fever virus) would now allow the spread of small localised outbreaks of HIV to involve people on a massive scale, and kick-start an epidemic.
But you'll notice that there is still one question left unanswered. How did the SIV get from the chimpanzee into people (several times) in the first place ?
The most likely answer lies in the popular bush fare - monkey meat. The cut-hunter theory, as it is widely known, argues that someone out hunting primates contaminates a skin wound with SIV-infected blood, thereby infecting themselves with SIV / HIV. But is there any evidence that this is happening ?
The answer is yes, indirectly. Scientists recently discovered people in Cameroon infected with another monkey virus called SFV (simian foamy virus) which is also a retrovirus like HIV. The infected individuals all gave a history of having previously butchered and eaten monkey meat. This result shows that butchering monkeys and exposure to monkey blood can cause another (unrelated) virus to jump the species barrier and get into people. If SFV can perform this feat it is not unreasonable to presume that SIV/HIV may do the same.
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"I never forget a face, but in your case I'll make an exception"
- Groucho Marx
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Wouldn't have wanted to be one of the scientists on the monkey sh-t team....
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I thought that for several years scientists had denied the suspicion of ape to human contact being a possible cause of AIDS, then I read on webmd that it was part of the timeline. Specifically the theory stated above by Chris. So upon Googling the theory I found this article. I know there's still alot of uncertainty, but I'm blown away by this.
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There is no doubt that the ancestor of HIV is SIV, the form of the virus carried by different species on non-human primates. But in claiming to be surprised that this species jump could have happened, what people do not realise is that it has happened many times in history. HIV-1 and HIV-2 are very different virological entities and can be traced back to two quite distinct primate carriers, chimps in the case of HIV-1 and sooty mangabeys in the case of HIV-2. What this tells us is that the likelihood of apparently improbable jumps like this occurring is not so low after all.
Chris