Ever since the controversial announcement by Dr. Robert Gallo of the National Cancer Institute of USA in 1984* of the recognition of HIV as the cause of AIDS, speculations seethed about the descent of the virus. Some fertile minds even went to the extent of dubbing it a direct product of molecular biology, created by evil scientists in a secret lab sometime in the early seventies. Other, more cautious ones, postulated that the virus was passed on from apes to humans through trans-species transmission.

The problem with the former theory is that even today, molecular biology cannot cope with such intractable virus as HIV is, much create it from scratch some thirty years ago. And the trouble with the second postulate was that scientists were unable to identify anything like HIV from any primate species.

Up till now, only three chimpanzees infected with HIV-like viruses have been documented. Two of these belonged to the sub-species Pan troglodytes troglodytes, and the third was a member of Pan troglodytes schweinfurthii. But the viruses were so different ¾ especially in the last species ¾ from HIV that it was troublesome to establish a clear-cut connection.

Now researchers from the University of Alabama at Birmingham, USA, have isolated a strain of lentivirus SIVcpzUS from another member of P. t. troglodytes. The research team, led by Dr. Beatrice Hahn, sequenced the genome of SIVcpzUS and determined by mitochondrial DNA analysis that it and all HIV-1 strains known to infect man (M, N and O), are close relations. The UAB researchers further found that the natural habitat of P. t. troglodytes coincides with areas where the above-mentioned types of HIV are endemic: Cameroon, Equatorial Guinea, Congo and Central African Republic. This bit of information nicely puts the pieces of the puzzle together ¾ establishing that P. t. troglodytes is in fact the primary source and reservoir of HIV.

Like many other scientific breakthroughs, this discovery was also not without its share of serendipity. One day in 1998, Larry Arthur of the American National Cancer Institute's AIDS Vaccine Program was cleaning his specimen freezers when he stumbled on to some 13 year old frozen blood tissues. The tag read something like this: Marilyn; age 26; died in childbirth. The preserved specimen was from a lab chimp that had died in 1985. Dr. Arthur handed these samples to Dr. Hahn to see if there was something in them for her. The rest is history.

There are three sub types of HIV: M (responsible for the pandemic), N and O, which are confined to the West Equatorial Africa.

The cross-species transmission, called zoonosis, may have been going on for centuries in Africa, where "bushmeat" trade is in vogue and chimpanzee steak is a considered a delicacy. Unsuspecting hunters, who still use primitive butchery techniques, may expose themselves through open wounds in their hands or other body parts while skinning the corpses of infected chimpanzees. People may have been contracting AIDS and dying of it in their villages without having a clue to the causes of their disease. Because of great difficulties involved in the cross-continental travel, AIDS remained confined for centuries in Central Africa. It was only after establishment of the so-called "World Wide Web" of international air travel in the later part of the twentieth century, coupled with increased sexual promiscuity due to the advent of the pill, that AIDS started propagating throughout the globe. Today, about 35 million people are thought to be infected with HIV in the world.

This discovery is important not only because it puts to rest a decades-old controversy, it can also help find a cure for the scourge. Having established that HIV originated from a particular sub-species of chimpanzees, and because more than 98% of the genetic material of chimpanzees is identical with that of humans, new treatments can be discovered for the treatment or prophylaxis of AIDS, given that the SIV does not cause AIDS in chimps.

Certainly, more studies of wild infected chimps are required to meet this end. But there is a problem. Due to the rampaging bushmeat trade, the chimpanzee population curve is taking a nose-dive. Unless measures are taken to prevent the slaughter of this closest relative of man, the species will become extinct, perhaps burying with itself a potential cure of AIDS.

Meanwhile, AIDS has climbed to the number four spot on the roster of lethal diseases, up three notches from the previous year. According to a report published by the World Health Organization in May 1999, AIDS is now only behind ischemic heart disease, cerebrovascular disease and acute lower respiratory disease on the ladder of killer diseases. In Africa, the situation is even grimmer. AIDS is now the leading killer there, outranking malaria as the most deadly ailment of the Dark Continent.

*NCI had to fight a long battle with the Pasteur Institute in France, which also laid claim to the discovery of HIV.

References:

1. Gao, Feng, et al. Origin of HIV-1 in the Chimpanzee Pan troglodytes troglodytes. Nature. 1999;397:436-441
2. Weiss, Robin, Wrangham, W. From Pan to pandemic. Nature. 1999; 397