The other AIDS epidemic
Twenty years after the first AIDS virus was identified, news about a second
“A RETROVIRUS belonging to the family of recently discovered human T-cell leukaemia viruses (HTLV), but clearly distinct from each previous isolate, has been isolated from a Caucasian patient with signs and symptoms that often precede the acquired immune deficiency syndrome (AIDS).”
With these words, in a paper published 20 years ago this week in Science, Luc Montagnier of the Pasteur Institute in Paris announced that he had isolated the virus that causes AIDS. He called it LAV (lymphadenopathy-associated virus). Now, after a priority dispute with Robert Gallo, an American researcher who claimed to have discovered it independently, and who called it HTLV-3, it has become more familiar under its compromise moniker, the human immunodeficiency virus, HIV.
In the decades since Dr Montagnier's paper, HIV has run riot. The latest report on the epidemic, issued on May 13th by the Global HIV Prevention Working Group, a committee of the great and good, reiterated how bad things are. If nothing changes, the world faces 45m new infections between now and 2010. And what needs to change, naturally, is that more money must be spent on prevention. The group thinks that tripling global spending to $5.7 billion by 2005 would be enough to do the job.
That would certainly be wise. But in all the brouhaha, it is easy to forget that the full name of the virus is HIV-1. For in 1986 a second AIDS-causing agent, now known as HIV-2, was isolated by Dr Montagnier's laboratory. And an important aspect of this virus's spread has just been elucidated in a paper in the Proceedings of the National Academy of Sciences.
HIV-2 has not rampaged to the same extent as HIV-1. It is more or less confined to West Africa, and it is believed to infect “only” about 1m people (HIV-1 infects more than 40m). Unlike HIV-1, which seems to be a chimpanzee virus that leapt the species barrier to infect people, HIV-2 came from a monkey called the sooty mangabey. When that happened, and exactly how the virus subsequently got its grip, have remained unclear. Until, that is, Anne-Mieke Vandamme, of the University of Leuven, Belgium, and her colleagues, examined the virus's genetic material. Now, they think they know.
HIV-2 seems to have leapt the species barrier twice, once in 1940, and again in 1945. These dates, though hedged within generous margins of error, can be estimated by looking at infected tissue samples taken at various times since, seeing how the virus's genetic sequence has changed over the years, and extrapolating backwards.
This explains a paradox about HIV-2's origin and spread. The evidence on the ground suggests that it started in Guinea-Bissau, in the 1960s, when that country was a Portuguese colony. But sooty mangabeys were extinct in the area by then. In the 1940s, though, they still thrived.
What seems to have happened, according to the genetic sequences, is that the virus was rare until the 1960s, and then started to spread rapidly. Its spread coincided with Guinea-Bissau's war of independence from Portugal, which began in 1963 and went on until 1974. War, with its attendant movement of armies of sexually active young men, provides an ideal climate for the spread of a virus such as HIV-2. Before the war started, it was confined to the colony. Afterwards, it spread not only around Guinea-Bissau, but to many of the country's neighbours as well. When sorrows come, they come not as single spies, but in battalions.
This article appeared in the Science & technology section of the print edition under the headline "The other AIDS epidemic"
From the May 17th 2003 edition
Discover stories from this section and more in the list of contentsExplore the edition
It’s not clear why
It can grow to be a centimetre long
A new study calls into question a published clinical trial