The Chimp and the River: How AIDS Emerged from an African Forest

by David Quammen

  The second surprise came once he extracted viral fragments from the samples, amplified those fragments, sequenced them, and fed the genetic sequences into a program that would compare these new strains with many other known strains of SIV and HIV. The program expressed its comparisons in the form of a most-probable phylogeny—a family tree. Keele recalled watching the results for a certain chimp, an individual labeled LB7, whose feces had been collected at Lobeke. “We were just shocked,” he said. “I mean, I had ten people around my computer, all waiting to see what that sequence looked like.” What it looked like was the AIDS virus.

  When his computer delivered its latest tree, LB7’s isolate of SIVcpz showed up as a twig amid the same little branch that held all known human strains of HIV-1 group M. (In scientific lingo, it fell within the same clade.) It was at that point “the closest thing” to a match, Keele told me, that had ever been found in a wild chimp. “And then we find more, right? The more we dig, the more we find.” The other close matches came from that same little area: southeastern Cameroon. A chilling, historic epiphany, at which Keele and his colleagues were thrilled. “You can’t make this stuff up, as Beatrice would say. It’s too good.” Their joy lasted about ten seconds, after which everyone became hungry for more samples and more results. Your celebration is always provisional, Keele told me, until you’ve written the paper and gotten that congratulatory note of acceptance from the editors of Science.

  Keele and the group now sequenced entire genomes (not just fragments) from four samples, all collected in the same area, and on those sequences ran their genetic analyses again. Again they found the new SIVcpz shockingly similar to HIV-1 group M. The similarity was so close as to leave almost no chance that any other variant, yet undiscovered, could be much closer. Hahn’s lab had located the geographical origin of the pandemic: southeastern Cameroon.

  12

  So much for where as well as when. AIDS began with a spillover from one chimp to one human, in or near that small southeastern wedge of Cameroon, around 1908 (give or take a margin of error). From there it grew, slowly but inexorably, from a spillover to an outbreak to a pandemic. That leaves our third question: how?

  The Keele paper appeared in Science, on July 28, 2006, under the title “Chimpanzee Reservoirs of Pandemic and Nonpandemic HIV-1.” In addition to Brandon Keele as first author, there was the usual list of coauthors, including Mario Santiago, Martine Peeters, several partners from Cameroon, and last again, Beatrice H. Hahn. The data were fascinating, the conclusions were judicious, the language was careful and tight. Near the end, though, the authors let supposition fly:

  We show here that the SIVcpzPtt strain that gave rise to HIV-1 group M belonged to a viral lineage that persists today in P. t. troglodytes apes in southeastern Cameroon. That virus was probably transmitted locally. From there it appears to have made its way via the Sangha River (or other tributaries) south to the Congo River and on to Kinshasa where the group M pandemic was probably spawned.

  But the phrase “transmitted locally” was opaque. What mechanism, what circumstances? How did those crucial events occur and proceed?

  Hahn herself, along with three coauthors, had addressed that back in 2000, when she first argued the idea that AIDS is a zoonosis: “In humans, direct exposure to animal blood and secretions as a result of hunting, butchering, or other activities (such as consumption of uncooked contaminated meat) provides a plausible explanation for the transmission.” She was alluding to the cut-hunter hypothesis. More recently she addressed it again: “The likeliest route of chimpanzee-to-human transmission would have been through exposure to infected blood and body fluids during the butchery of bushmeat.” A man kills a chimpanzee and dresses it out, hacks it up, in the course of which he suffers blood-to-blood contact through a cut on his hand. SIVcpz passes across the species boundary, from chimp to human, and taking hold in the new host becomes HIV. This event is unknowable in its particulars but it’s plausible, and it fits the established facts. Some variant of the cut-hunter scenario, occurring in a forest of southeastern Cameroon around 1908, would account not just for Keele’s data but also for Michael Worobey’s timeline. But then what? One man in southeastern Cameroon is infected.

  “If the spillover occurred there,” I asked Hahn, “how was it that the epidemic began in Kinshasa?”

  “Well, there are lots of rivers going down from that region to Kinshasa,” she said. “And the speculation, the hypothesis, is that is how the virus traveled—in people, not in apes. It wasn’t the apes that got into the canoe for a little visit of Kinshasa. It was the people who carried the virus down, most likely.” Sure, she acknowledged, there was a slim chance that someone might have brought a live chimp, captive, infected, all the way down from the Cameroonian wedge—“but I think it is highly unlikely.” More likely the virus traveled in humans.

  Sexual contacts in the villages kept the chain of infection alive, though barely, by this line of speculation, and the disease didn’t explode as a notable outbreak—not for a long while. When someone died of immunodeficiency, the death may have seemed unremarkable amid all other sources of mortality. Life was hard, life was perilous, life expectancy was short even apart from the new disease, and many of those earliest HIV-positive people may have succumbed to other causes before their immune systems failed. There was no epidemic. But the chain of infection sustained itself. Each HIV-positive person infected, on average, at least one other person. The virus seems to have traveled just as people traveled in those days: mainly by river. It made its way out of southeastern Cameroon along the headwaters of the Sangha River, then down the Sangha to the Congo, then down the Congo to Brazzaville and Léopoldville, the two colonial towns on either side of a huge broadening of the river, which was then known as the Stanley Pool. “Once it got into an urban population,” Hahn said, “it had an opportunity to spread.”

  But still it moved slowly, like a locomotive just leaving the station. Léopoldville contained fewer than ten thousand people in 1908, and Brazzaville was even smaller. Sexual mores and the fluidity of interactions were unlike what prevailed in the boondocks, but not yet so unlike as they would become. The arithmetic of the outbreak was still modest, with scarcely more than a single transmission onward per infected person. In the language of disease ecologists: the basic reproduction rate (the average number of secondary infections from each primary infection at the beginning) barely exceeded 1.0, the minimal level required for the outbreak to continue indefinitely. Then, as time passed, more people drifted into the towns, drawn by the prospect of working for wages or selling their goods. Habits and opportunities changed. Women came as well as men, though not so many of them, and among those who did, more than a few entered the sex trade.

  By 1914, Brazzaville contained about six thousand people and was “a hard mission field,” according to one Swedish missionary, where “hundreds of women from upper Congo are professional prostitutes.” It was the capital of the colony then known as French Equatorial Africa. The male population included French civil servants within the colonial administration, soldiers, traders, and laborers, and they probably outnumbered females by a sizable margin, due to colonial policies that discouraged married men, coming there to work, from bringing their families. That gender imbalance heightened the demand for commercial sex. But the format for bought favors, in those early years, was generally different from what the word “prostitute” might suggest—grindingly efficient, wham-bam encounters with a long succession of strangers. Instead there were single women, known as ndumbas in Lingala and femmes libres in French, “free women” as distinct from wives or daughters, who would provide their clients with a suite of services, ranging from conversation to sex to washing clothes and cooking. One such ndumba might have just two or three male friends who returned on a regular basis and kept her solvent. Another variant was the ménagère, a “housekeeper” who lived with a white colonial official and did more than keep house. Commercial arrangements, yes, but these didn’t represent th
e sort of prodigiously interconnected promiscuity that could cause a sexually transmitted virus to spread widely.

  Across the pool in Léopoldville, meanwhile, the disparity of genders was even worse. This town was essentially a labor camp, controlled by its Belgian administrators, inhospitable to families, where the male-female ratio in 1910 was ten to one. Travel through the countryside and entry into Léopoldville were restricted, especially for adult females, though some women managed to get false documents or evade the police. If you were a restless, imaginative girl in one of the villages, poorly fed and poorly treated, to be a ndumba in Léopoldville could well have seemed enticing. Here too, though, even with ten horny men for each woman, commercial sex didn’t happen in brothels or by streetwalking. Free women had their special friends, their clients, maybe several contemporaneously, but there was no dizzying permutation of multiple sexual contacts, not yet. One expert has called this “a low-risk type of prostitution,” with regard to the prospects of HIV transmission.

  Léopoldville also supported a lively market in smoked fish. Ivory, rubber, and slaves were traded there, for export, with profits going mainly to white concessionaires, well into the colonial era. Although a deep canyon and a set of forbidding cataracts stood between the Stanley Pool and the river’s mouth, isolating both cities from the Atlantic Ocean, a portage railway built in 1898 had breached that isolation, bringing more goods and commerce, which brought more people, and in 1920 Léopoldville replaced a downriver town as capital of the Belgian Congo. By 1940, its population had edged up to forty-nine thousand. Then the demographic curve steepened. Between 1940 and independence, which came in 1960, the city grew by almost an order of magnitude, to about four hundred thousand people. Léopoldville became Kinshasa, a twentieth-century African metropolis, where life was very different from what passed in a Cameroonian village. The tenfold population increase, along with the concomitant changes in social relations, might go a long way to explain why HIV “suddenly” took off. By 1959, the ZR59 carrier was infected, and a year later in the same city the carrier of DRC60 too. By that time the virus had proliferated to such a degree, mutating and diversifying, that DRC60 and ZR59 represented quite different strains. The basic reproduction rate now must have well exceeded 1.0, and the new disease spread—through the two cities and eventually beyond. “You know,” Hahn said, “a virus was at the right place at the right time.”

  When I read Keele’s presentation of the chimp data and the analysis, in early 2007, my jaw dropped like a pound of ham. These folks had located Ground Zero, if not Patient Zero. And when I looked at the map—Figure 1 in Keele’s paper, showing the Cameroonian wedge and its surroundings—I saw places I knew. A village where I had slept, on my way to a Congo assignment for National Geographic. A river I had ascended in a motor pirogue. It turned out that, seven years earlier, during an arduous footslog expedition through the forests of the Republic of the Congo and Gabon, with an American ecologist named J. Michael Fay, he and I and his forest crew had passed very near the cradle of AIDS.

  After talking with Beatrice Hahn, I thought it might be illuminating to go back.

  13

  Douala is a city on Cameroon’s western coast, with a seaport and an international airport. I escaped it, with my own crew, as quickly as possible. We rode east in a beat-up but sturdy Toyota truck, leaving at dawn, getting ahead of the crush, our gear stashed under tarps in the pickup’s bed. Moïse Tchuialeu was my driver, Neville Mbah my Cameroonian fixer, and Max Mviri, from the Republic of the Congo, was along to handle things when we reentered his country in the course of the crazy loop I had planned. Max and I had flown up from Brazzaville the night before. We were a genial foursome, eager to move after the hassles of preparation, rolling past the closed shops and the billboards to the city’s eastern fringe, where traffic thickened in a haze of blue diesel exhaust and the outlier markets were already open for business, selling everything from pineapples to phone minutes. Highway N3 would take us straight to Yaoundé, Cameroon’s inland capital, and then another big two-lane onward from there.

  During a stop in Yaoundé, around midday, I met with a man named Ofir Drori, head of an unusual group called LAGA (the Last Great Ape Organization) that helps government agencies in Central Africa enforce their wildlife-protection laws. I wanted to see Drori because I knew that LAGA was especially engaged on the problem of apes’ being killed for bushmeat. I found him to be a lean Israeli expat with dark, alert eyes and a patchy goatee. Wearing a black shirt, black jeans, a black ponytail, and an earring, he looked like a rock musician or, at least, a hip New York waiter. But he seemed to be a serious fellow. He had come to Africa as an adventure-seeking eighteen-year-old, Drori told me, and gotten involved with human-rights work in Nigeria, then moved to Cameroon, did a little gorilla journalism (or was it guerrilla journalism?), and became a passionate antipoaching organizer. He founded LAGA, he said, because enforcement of Cameroon’s antipoaching laws had been terrible, nonexistent, for years. The group now provided technical support to investigations, raids, and arrests. Subsistence hunting for duikers and other abundant, unprotected kinds of animal is legal in Cameroon, but apes, elephants, lions, and a few other species were protected by law—and increasingly by actual enforcement. Perpetrators were finally getting busted, even doing time, for dealing in ape flesh and other contraband wildlife products. Drori gave me a LAGA newsletter describing the efforts to stem poaching of chimps and gorillas, and he warned me against the myth that ape hunting is a problem because local people are hungry. The reality, he said, is that local people eat duikers or rats or squirrels or monkeys—if they eat meat at all—whereas the fancy stuff, the illicit delicacies, the chimpanzee body parts, the gobs of elephant flesh, the hippopotamus steaks, get siphoned away by upscale demand from the cities, where premium prices justify the risks of poaching and illegal transport. “What brings the money are the protected species,” he said. “Things that are rare.”

  Drori’s newsletter mentioned a raid against a hidden storage room, at a train station, that served at least three different dealers; the room had contained six refrigerators and its seized contraband included a chimpanzee hand. Another bust, against a dealer whose car had held fifty kilos of marijuana plus a young chimp with a bullet wound, suggested diversified wholesale commerce. And if chimp meat travels toward money, chimp viruses presumably do too. “If you’re thinking about infection,” he said, knowing that I was, “don’t just think of villages.” Any chimpanzee killed in the southeastern corner of the country, including an SIV-positive individual, might easily end up here in Yaoundé, being sold for meat in a back alley or served through a very discreet restaurant.

  We left the city in early afternoon, headed eastward again, moving against a stream of log trucks hammering toward us in the opposite lane, each one burdened to capacity with a load of just five or six gigantic stems. Somewhere out there, in that sparsely populated corner of the country, old-growth forests were being sheared. Around sundown we reached a town called Abong Mbang and stopped at the best local hotel, which meant running water and a lightbulb. Early next day, an hour beyond Abong Mbang, the blacktop ended though the log trucks kept coming, now on a ribbon of red clay. The temperature climbed toward midday equatorial heat and, wherever we encountered a little rain shower, the road steamed in red. Elsewhere the landscape was so dry that powdery red clay dust rose on the gusts from passing vehicles, coating trees along the roadside like bloody frost. We hit a police checkpoint and endured a routine but annoying shakedown, which Neville handled with aplomb, making two phone calls to influential contacts, refusing to pay the expected bribe, and yet somehow recovering our passports after only an hour. This guy is good, I thought. The road narrowed further, to a band of arsenical red barely wider than a log truck, leaving us hugging the shoulder when we encountered one, and the forest thickened on both sides. Around noon we crossed the Kadéï River, greenish brown and slow, meandering southeast, a reminder that we were now at the headwaters of the Co
ngo basin. The villages through which we passed became smaller and looked progressively more spare and poor, with few gardens, little livestock, almost nothing for sale except bananas, mangoes, or a bowl of white manioc chips set out forlornly on an untended stand. Occasionally a goat or a chicken scampered out of our way. In addition to the log trucks, we now met flatbeds loaded with milled lumber, and I remembered hearing how such trucks sometimes carried a concealed stash of bushmeat, rumbling toward the black markets of Yaoundé and Douala. (A photographer and activist named Karl Ammann documented that tactic with a photo, taken at a road junction here in southeastern Cameroon, of a driver unloading chimpanzee arms and legs from the engine compartment of his log truck. The photo appeared in a book by Dale Peterson, titled Eating Apes, in which Peterson estimated that the human population of the Congo basin consumes roughly 5 million metric tons of bushmeat each year. Much of that wild meat—though no one knows just how much—travels out of the forest as contraband cargo on log trucks.) Apart from the trucks, today on this stretch of red clay, there was almost no traffic. By late afternoon we reached Yokadouma, a town of several thousand. The name translates as “Fallen Elephant,” presumably marking the site of a memorable kill.

  We found a local office of the World Wildlife Fund and, inside, two earnest Cameroonian employees named Zacharie Dongmo and Hanson Njiforti. Dongmo showed me a digital map plotting the distribution of chimpanzee nests in this southeastern corner of the country, which includes three national parks—Boumba Bek, Nki, and Lobeke. A chimpanzee nest is simply a small platform of interwoven branches, often in the fork of a smallish tree, which provides just enough support for the ape to sleep comfortably. Each individual makes one each night, though a mother will share hers with an infant. Tallying such nests, which remain intact for weeks after a one-night use, is how biologists estimate chimpanzee populations. The pattern on Dongmo’s map was clear: a high density of nests (and therefore of chimpanzees) within the parks, a low density outside the parks, and none at all in areas adjacent to the roads leading to Yokadouma. Logging and bushmeat were the reasons. Logging operations bring roads and workers and firearms into the depths of the forest; dead wildlife consequently travels out. Dongmo and Njiforti explained it as an informal, ad hoc form of commerce. “Most of the illegal trade is man-to-man,” Njiforti said. “A poacher meets you and says, I have meat.” But it’s also woman-to-man, he added: Much of the trading is done by “Buy ’em–Sell ’ems,” women who travel between villages as petty traders, dealing openly in cloth, or spices, or other staples, and covertly in bushmeat. Such a woman buys directly from the hunter, often paying in bullets or shotgun shells, and sells to whomever she can. Commerce is relatively fluid; many of these women have cell phones. And there are all sorts of tricks, Njiforti said, for getting the meat out. It could be tucked into a truckload of cocoa pods, for instance, a cash crop from this region. The police and the wildlife wardens may get tipped off, and they can stop a truck and search it, but at some risk to themselves. If you stop a truck and demand it be unloaded, and then there’s no illegal cargo, Njiforti said, “the guy can sue you. The information has to be very good.” That’s why Ofir Drori’s network has proved itself useful.