Thursday, February 10, 2005

AIDS and Polio

Wolf's Monkey at Bronx Zoo
A correspondent wrote a few days ago asking if I knew anything about allegations that AIDS originated in an oral polio vaccine prepared using chimpanzee kidneys.

It sounded very vaguely familiar, though it didn't sound so different from the stories about the CIA creating AIDS. I was, to be frank, skeptical. So I poked around and found some facts, and my correspondent explained how he was hearing about it. The Sundance channel is running a documentary on this, based on The River : A Journey to the Source of HIV and AIDS by Bill Hamilton, Edward Hooper. I haven't read the book, and I don't get Sundance, so a tape of the show is winging its way to me. Meanwhile, I have Google.

The CDC has a nice FAQ on this issue. Hooper has a longish argument here, where he goes after some of the arguments that follow.

The story, in brief is as follows. In 1957-60, Hilary Koprowski was administering oral polio vaccines (OPV) in Africa. The vaccine was cultured in monkey kidneys. The manufacturers say that rhesus monkeys donated the kidneys, Hooper suggests that chimp kidneys were used too. Several places where OPV was administered also had some of the first AIDS diagnoses.

There are two strains of HIV: HIV-1 and HIV-2. HIV-2 is almost genetically identical to SIVsm (simian immunodeficiency virus) found in sooty mangabee monkeys, and almost certainly originated in them. HIV-1 almost surely originated in chimps, but the exact population of origin is unknown, because known SIVcpz strains in chimps are more different from HIV-1 than SIVsm is from HIV-2.

I will point out that the current polio vaccine is not related in any way with the polio vaccine in question. The modern vaccine has been tested extensively, and is very safe.

It turns out, samples of the old vaccine have been tested too, and also seem safe. But that's jumping ahead.

Hooper suggests that extra chimps were bought on the market in Zaire and their kidneys used to produce extra vaccine. Koprowski says the chimps were only for safety testing, and were never used to manufacture vaccine. Hooper suggests that the medical and scientific establishment has covered up evidence that vaccines spread AIDS because it would turn people against vaccines. He claims that all samples have been kept within a community of sympathetic scientists, and questions the results of tests performed on samples.

As in all science, we proceed from hypothesis to predictions. If HIV originated from these vaccine lots, AIDS should have been documented throughout the areas vaccinated. The same lot was used in Poland and the Belgian Congo; no AIDS cases appear to have resulted from the Polish vaccinations.

We can predict that the genetic divergence of HIV-1 from SIVcpz should be around 1957. Molecular clock based work (pdf) suggests a divergence in 1931, with 95% confidence intervals from 1915-1941. This means that, examining rates of genetic change in recent years and extrapolating back from known HIV-1 strains, all the trajectories for a graph of changes versus year put zero changes around 1931, and almost certainly not after 1950. While assumptions can be challenged, this work looks very solid. All the different lines of evidence they used gave similar results, and their assumptions and methods are all reasonable. Molecular clocks are not my area of expertise, but neither I nor the editors and reviewers at Science have objections.

Hooper claims that they have methodological flaws, but it's unlikely that the process he discusses would have a significant effect on the result. At the very least, there is no reason to expect that this would bias the results in any particular direction, so we might be making the origin too recent.

If chimps were used to produce the vaccines, chimp DNA would be in the samples. If HIV-1 originated from SIV in the vaccine, the vaccine should have SIV. Tests in seven different labs found neither SIV nor chimp DNA in samples of the vaccine, several of which were labeled as being from the lots used in Africa. If rhesus monkeys were used in producing the vaccine, you would expect to find rhesus DNA, and all seven labs did.

Hooper argues that chimp kidneys may have been used in the field to produce more vaccine. The chimps throw a monkey-wrench in that argument.

If chimps from the area were the origin of SIV, you'd expect them to be infected with the most similar form of SIV to HIV-1. While local chimps are infected, their strain is very different from HIV-1 (pdf).

That last paper raises some complicated issues. The title is “Contaminated polio vaccine theory refuted” which suggests that this is the final nail in the coffin. In fact, this is the weakest piece of evidence. Hooper claims to have evidence that chimps were transported to the research facilities from all over. While demonstrating that HIV-1 probably originated somewhere in west central Africa, not around Kisangani, is important, that can be explained away. The other evidence all points to a different mechanism.

One suggestion is that dirty needles spread HIV-1. SIV contact is probably not a historic rarity. People hunt chimps for food, and in the butchering, it was likely that people got some body fluid contact and SIV infected people. Why didn't it start a rampant epidemic? Perhaps the doses were small enough for an immune response. Maybe most infections were rapidly fatal, so people didn't have time to spread it. Maybe slow transportation limited the disease's spread. By the 1930's transportation was cheaper and easier, so the disease may have gotten spread more widely through the population. Unsterile medical conditions may have allowed even more rapid spread of HIV.

It's even possible that vaccination teams were responsible for spreading AIDS even if the vaccines were sterile. They may have simply been spreading an existing infection through dirty needles. HIV doesn't last in the mouth or digestive system, so an oral vaccine is a poor candidate for the origin.

So, bottom line:
  • Modern vaccines are known to be safe.
  • The old vaccines test negative for infection and chimp DNA.
  • The local chimps carry the wrong SIV strain.
  • Other regions treated with the vaccine didn't experience HIV outbreaks.
  • HIV originated between 10 and 30 years before the vaccination campaign.
  • Therefore the old vaccine is almost certainly not the origin of HIV.
  • HIV-1 probably originated through the use of dirty needles in combination with natural SIV infections.

In a few days, I'll blog the bigger issue: why are people so willing to believe a conspiracy theory about scientists and vaccines. But maybe I'll leave that to someone on Skeptic's Circle or Grand Rounds.

Monkey Gone to Heaven” by The Pixies from the album Doolittle (2003, 2:56).