Chimp to man The circuitous path of AIDS

Researcher sifts a blizzard of scientific papers and works out the most likely path the virus took

It involves chimps and monkeys, hunters and butchers, ‘free women’ and prostitutes, syringes and plasma-sellers, evil colonial lawmakers and decent colonial doctors with the best of intentions. And a virus that, against all odds, appears to have made it from one ape in the central African jungle to one Haitian bureaucrat leaving Zaire for home and then to a few dozen men in California gay bars before it was even noticed – about 60 years after its journey began.

Most books about AIDS begin in 1981, when gay American men began dying of a rare pneumonia. In ‘The Origins of AIDS,’ published last week by Cambridge University Press, Dr Jacques Pepin, an infectious disease specialist at the University of Sherbrooke in Quebec, performs a remarkable feat.

Pepin sifts the blizzard of scientific papers written about AIDS, adds his own training in epidemiology, his own observations from treating patients in a bush hospital, his studies of the blood of elderly Africans, and years of digging in the archives of the European colonial powers, and works out the most likely path the virus took during the years it left almost no tracks.

Working slowly forward from 1900, he explains how Belgian and French colonial policies led to an incredibly unlikely event: A fragile virus infecting a small minority of chimpanzees slipped into the blood of a handful of hunters, one of whom must have sent it down a chain of ‘amplifiers’—disease eradication campaigns, red-light districts, a Haitian plasma centre and gay sex tourism. Without those amplifiers, the virus would not be what it now is: a grim pilgrim atop a mountain of 62 million victims, living and dead.

In the early 1980s, Pepin was a young doctor fighting a sleeping sickness epidemic at a hospital in Nioki, in what was formerly the Belgian Congo, then Zaire, and is now the Democratic Republic of Congo. The virus was then unknown in Africa, but his work gave him clues that would later help him on its trail. In retrospect, he says in his book, he may have inadvertently infected some of his patients. Ideally, the glass syringes used in Nioki were sterilised in the hospital’s autoclave. But with the electricity often out, nurses boiled them instead. “And I did not pay too much attention to how long they were boiled,” he said in an interview.

Later, he worked in Guinea-Bissau on HIV-2, which is related to HIV-1 but causes a milder and harder-to-transmit form of AIDS that some victims live with for decades.

Noting that cases were more common among older people, he concluded that it was dying out. If sexual transmission among young people was not keeping it alive, he reasoned, some other route must have first made it so widespread among the elderly. He suspected the aggressive campaigns that colonial doctors waged against syphilis, yaws, leprosy, tuberculosis and other ills until independence arrived in the 1960s. They all used injections, since pill versions of many antibiotics did not exist or were costly.

Surprisingly complex

Blood and tissue samples stored in freezers in Africa and in European hospitals that treat Africans—a few going back to the 1950s – form a map of AIDS viral subtypes, which is surprisingly complex. For example, white and black South Africans have different subtypes. Simian immunodeficiency virus, which infects monkeys and apes, is similarly mapped; it was first found in zoo animals, but now is tracked by jungle teams who extract DNA from feces.

The ancestor to AIDS is in one chimpanzee subspecies, Pan troglodytes, which in nature lives only between the Sanaga and Congo Rivers. (Chimpanzees can’t swim.) It is a blend of simian viruses from red-capped mangabeys and mustached guenons, small monkeys that chimps hunt and eat.

From colonial archives in Paris, Marseilles, Brussels, Lisbon and London, Pepin dug out old records of clinics where, as early as 1909, African prostitutes were required to have venereal disease inspections. He went through stacks of newspapers, like the Voix du Congolais, which wrote extensively about polygamy and prostitution, and pored over studies by European ethnographers. (His own fluency in French was crucial, of course.)

In brief, his recounting of the epic journey is this: In nature, only about 6 per cent of troglodyte chimps are ever infected. Within a troop, each female mates with many males, but mating with outsiders is rare, so most troops are untouched while a few are heavily infected. HIV-1’s four genetic groups, M, N, O and P, show that it made the chimp-human jump at least four times in history. But group M accounts for more than 99 per cent of all cases.

Why did only one spread?

Molecular clock dating shows that M reached humans somewhere near 1921.

Chimpanzees are too big and agile to be hunted with anything but guns, which until the 20th century were almost entirely in white hands. Using colonial census data, surveys of how modern bush-meat hunters butcher kills, and infection rates among nurses stuck by dirty needles, Pepin calculates that, in the early 1920s, a maximum of 1,350 hunters might have had blood-to-blood contact with troglodytes chimps.

Only 6 per cent of the chimps – about 80 – would have been infected, and fewer than 4 per cent of the scratched hunters probably could have caught it. That would suggest only three infected hunters at most.

Given how inefficient most sexual spread is – in some cases, a husband and wife can have sex for months without passing it – sex alone would not have let three hunters, or even a dozen, pass on their virus to today’s millions, he argues. There must have been an amplifier.

The next link was Haiti. Because white Belgians never trained an African elite, only about 30 Congolese outside the priesthood had university degrees at independence.

To fill the gap, the United Nations hired bureaucrats and teachers from abroad.

About 4,500 Haitians answered the call; they were black, well educated, French-speaking and eager to earn more than they could at home.

Now Pepin’s calculations get slightly more speculative. Group M of HIV-1 is, in turn, broken into subgroups A through K. Haiti’s epidemic, like that of North America and Western Europe, is nearly all subgroup B. But subgroup B is so rare in central Africa that it causes less than 1 percent of cases. That suggests AIDS crossed the Atlantic in just one Haitian. Molecular clock dating indicates it reached Haiti roughly in 1966.

Once again, Pepin argues that rapid expansion through sex alone is mathematically impossible and that there must have been an amplifier. He believes the culprit was a Port-au-Prince plasma centre called Hemo-Caribbean that operated only from 1971 to 1972 and was known to have low hygiene standards.

Haiti was also a prime destination for gay US sex tourists; the Spartacus travel guides described how much young men expected to be paid. By the early 1980s, subgroup B was killing both US homosexuals and hemophiliacs, suggesting it arrived via both routes. The modern history of AIDS had begun.

Along the way, Pepin debunks other origin myths. The most grotesque was what he called the ‘surgical Viagra’ fad of the 1920s. About 2,000 American and European men – mostly rich, old and impotent – had chimpanzees’ testicles implanted in their scrota. The fad died after the word of tissue rejection spread, and after a few women had chimp ovary implants, which scandalised editorial writers who suggested they would give birth to ape-human hybrids.