Spillover: Animal Infections and the Next Human Pandemic (55 page)

Downstream from Moloundou, the last Cameroonian outpost on the Ngoko River is Kika, a logging town with a big mill that provides jobs and lodging for hundreds of men and their families, plus a dirt airstrip for the convenience of its managerial elite. There was no direct riverside road (why would there be? the river
is
a road) so we circled back inland to get there. Arriving in Kika, we reported promptly to the police station, a small shack near the river that served also as immigration post, where an officer named Ekeme Justin roused himself, pulled on his yellow T-shirt, and performed the necessary formalities for me and Max: stamping our passports
sortie de Cameroon.
We would exit the country here. Officer Justin, upon receipt of a fee for his stamp work, became our great friend and host, offering us tent space there beside the police post and help in finding a boat. He went off to town with Neville, the all-purpose fixer, and by sunset they had arranged charter of a thirty-foot wooden pirogue, with an outboard, capable of getting Max and me to Ouesso.

I was up at five the next morning, packing my tent, eager to turn the corner on this big loop and head back into Congo. Then we waited through a heavy morning rain. Finally came our boatman, a languid young man named Sylvain in a green tracksuit and flip-flops, to mount his outboard and bail the pirogue. We loaded, covered our gear with a tarp against the lingering drizzle, and after warm goodbyes to the faithful Neville and Moïse, also Officer Justin, we launched, catching a strong current on the Ngoko. We pointed ourselves downriver. For me, of course, this journey was all about the cut-hunter hypothesis. I wanted to see the route HIV-1 had traveled from its source and imagine the nature of its passage.

99

L
et’s give him due stature: not just a cut hunter but the Cut Hunter. Assuming he lived hereabouts in the first decade of the twentieth century, he probably captured his chimpanzee with a snare made from a forest vine, or in some other form of trap, and then killed the animal with a spear. He may have been a Baka man, living independently with his extended family in the forest or functioning as a sort of serf under the “protection” of a Bantu village chief. But probably he wasn’t, given what I’d heard of Baka scruples about eating ape. More likely he was Bantu, possibly of the Mpiemu or the Kako or one of the other ethnic groups inhabiting the upper Sangha River basin. Or he may have been a Bakwele, involved in the practice of beka. There’s no way of establishing his identity, nor even his ethnicity, but this remote southeastern corner of what was then Germany’s Kamerun colony offered plenty of candidates. I imagine the man thrilled and a bit terrified when he found a chimpanzee caught in his snare. He had proved himself a successful hunter, a provider, a proficient member of his little community—and he wasn’t yet cut.

The chimp too, tethered by a foot or a hand, would have been terrified as the man approached, but also angry and strong and dangerous. Maybe the man killed it without getting hurt; if so, he was lucky. Maybe there was an ugly fight; he might even have been pummeled by the chimp, or badly bitten. But he won. Then he would have butchered his prey, probably on the spot (discarding the entrails but not the organs, such as heart and liver, which were much valued) and probably with a machete or an iron knife. At some point during the process, perhaps as he struggled to hack through the chimp’s sternum or disarticulate an arm from its socket, the man injured himself.

I imagine him opening a long, sudden slice across the back of his left hand, into the muscular web between thumb and forefinger, his flesh smiling out pink and raw almost before he saw the damage or felt it, because his blade was so sharp. And then immediately his wound bled. By a lag of some seconds, it also hurt. The Cut Hunter kept working. He’d been cut before and it was an annoyance that barely dimmed his excitement over the prize. His blood flowed out and mingled with the chimp’s, the chimp’s flowed in and mingled with his, so that he couldn’t quite tell which was which. He was up to his elbows in gore. He wiped his hand. Blood leaked again into his cut, dribbled again into it from the chimp, and again he wiped. He had no way of knowing—no language of words or thoughts by which to conceive—that this animal was SIV-positive. The idea didn’t exist in 1908.

The chimpanzee’s virus entered his bloodstream. He got a sizable dose. The virus, finding his blood to be not such a different environment from the blood of a chimp, took hold.
Okay, I can live here.
It did what a retrovirus does: penetrated cells, converted its RNA genome into double-stranded DNA, then penetrated further, into the cells’ nuclei, and inserted itself as DNA in the DNA genome of those host cells. Its primary targets were T cells of the immune system. A certain protein receptor (CD4) on the surface of those cells, in the Cut Hunter, was not very different from the equivalent receptor (another CD4) on the T cells of the butchered chimpanzee. The virus attached, entered the human cells, and made itself at home. Once integrated into the cellular genome, it was there for good. It was part of the program. It could proliferate in two ways: by cell replication (each time an infected T cell copied itself, the retroviral genome was copied also) and by activating its little subgenome to print off new virions, which then escaped from the T cell and floated off to attack other cells. The Cut Hunter was now infected, though apart from a slash on the hand he felt fine.

Forget about Gaëtan Dugas. This man was Patient Zero.

Maybe he carried the chimp carcass, or parts of it, back to his village in triumph—as the boys of Mayibout 2 later carried an Ebola-filled chimp carcass back to theirs. Maybe, if he was Baka, he delivered the whole thing to his Bantu overlord. He didn’t want to eat it anyway. If he was Bantu himself, his family and friends feasted. Or maybe the chimp was a windfall from which he could afford to take special profit. If the season had been bounteous, with some duikers or monkeys killed, some forest fruits and tubers to eat, a good crop of manioc, so that his family wasn’t starving, he may have lugged his chimpanzee to a market, like the one in Moloundou, and traded for cash or some valuable item, such as a better machete. In that case, the meat would have been parceled out retail and many people may have eaten bits of it, either roasted or smoked or dried. But because of how the virus generally achieves transmission (blood-to-blood or sexually) and how it doesn’t (through the gastrointestinal tract), quite possibly none of those people received an infectious dose of virus, unless by contact of raw meat with an open cut on the hand or a sore in the mouth. A person might swallow plenty of HIV-1 particles but, if those virions are greeted by stomach acids and not blood, they would likely fail to establish themselves and replicate. Let’s suppose that fifteen different consumers partook of the chimp meat and that they all remained fine. HIV-negative. Lucky folks. Let’s suppose that only the Cut Hunter became infected directly from the chimp.

Time passed. The virus abided and replicated within him. His infectiousness rose high during the first six months, as virions in multitude bloomed in his blood; then the viremia declined some as his body mounted an early immune response, while it still could, and leveled off, for a period of time. He noticed no effects. He passed the virus to his wife, eventually also to one of the four other women with whom he had sex. He suffered no immune deficiency—not yet. He was a robust, active fellow who continued to hunt in the forest. He fathered a child. He drank palm wine and laughed with his friends. And then a year later, let’s say, he died violently in the course of an elephant hunt, an activity even more perilous than butchering chimpanzees. He was one of seven men, all armed with spears, and the wounded elephant chose him. He took a tusk through the stomach, momentarily pinning him to the ground. You could see the tusk hole in the dirt afterwards, as though a bloody stake had been driven in and pulled. Of the men who scooped him up, the women who prepared him for burial, none had an open cut and so they were spared infection. His son was born HIV-negative.

The Cut Hunter’s widow found a new man. That man was circumcised, free of genital sores, and lucky; he didn’t become infected. The other woman who had been infected by the Cut Hunter took several partners. She infected one. This fellow was a local chief, with two wives and occasional access to young village daughters; he infected both wives and one of the girls. The chief’s wives remained faithful to him (by constraint of circumstance if not by choice), infecting no one. The infected girl eventually had her own husband. And so, onward. You get the idea. Although sexual transmission of the virus occurred less efficiently from female to male, and not all so efficiently from male to female, it was just efficient enough. After several years, a handful of people had acquired the virus. And then still more, in time, but not many. Social life was constrained by small population size, absence of opportunity, and to some degree mores. The virus survived with an
R
0
barely above 1.0. It passed to a second village, in the course of neighborly interactions, and then a third, but it didn’t proliferate quickly in any of them. No one detected a wave of inexplicable deaths. It smoldered as an endemic infection at low prevalence in the populace of that little wedge of terrain, between the Ngoko River and the upper Sangha, where life tended to be short and hard. People died young from all manner of mishaps and afflictions. If a young man, HIV-positive, was killed in a fight, no one knew anything about his blood status except that it had been spilled. If a young woman, HIV-positive, died of smallpox during a local outbreak, likewise she left no unusual story.

In some cases, during those early years, an infected person may have lived long enough to suffer immune failure. Then there were plenty of ready bugs, in the forest, in the village, to kill him or her. That wouldn’t have seemed remarkable either. People died of malaria. People died of tuberculosis. People died of pneumonia. People died of nameless fever. It was routine. Some of those people might have recovered, had their immune systems been capable, but no one noticed a new disease. Or if someone did notice, the report hasn’t survived. This thing remained invisible.

Meanwhile the virus itself may have adapted, at least slightly, to its new host. It mutated often. Natural selection was at work. Given a marginal increase in its capacity to replicate within human cells, leading to increased levels of viremia, its efficiency of transmission may have increased too. By now it was what we would call HIV-1 group M. A human-infecting pathogen, rare, peculiar, confined to southeastern Cameroon. Maybe a decade went by. The bug survived. Spillovers of SIV
cpz
into humans had almost certainly occurred in the past (plenty of chimps were butchered, plenty of hunters were cut) and resulted in previous chains of infection, but those chains had been localized and short. The smoldering outbreak had always come to a cold end. This time it didn’t. Before such burnout could occur, another person entered the situation—also hypothetical but fitted to the facts—whom I’ll call the Voyager.

The Voyager wasn’t a hunter. Not an expert and dedicated one, anyway. He had other skills. By my imagining, he was a fisherman. He lived not in a forest clearing like the one at Mambele but in a fishing village along the Ngoko River. I picture him as a river boy from childhood; he knew the water; he knew boats. He owned a canoe, a good one, sturdy and long, made from a mahogany log with his own hands, and he spent his days in it. He was a young man with no wife, no children, and just a bit of an appetite for adventure. He had fallen away from his natal community at an early age, becoming a loner, because his father died and the village came to despise his mother, suspecting her of sorcery based on a piece of bad luck and a grudge. He took this as a deep personal bruise; he despised the villagers in return, screw them, and went his own way. It suited him to be alone. He was not an observant Bakwele. He never got circumcised.

The Voyager ate fish. He ate little else, in fact, besides fish and bananas—and sometimes manioc, which he didn’t plant or process himself but which was easily acquired in trade for fish. He liked the taste and he loved the idea of fish, and there was always enough. He knew where to find fish, how to catch them, their varied types and names. He drank the river. That was enough. He didn’t make palm wine or buy it. He was self-sufficient and contained within his small world.

He provided fish to his mother and her two younger children, as I see him, a loyal son though an alienated neighbor. His mother still lived at the fringe of the old village. His surplus catch he dried on racks, or in wet season smoked over a fire, at his solitary riverbank camp. Occasionally he made considerable journeys, paddling miles upstream or drifting downstream, to sell a boatload of fish in one of the market villages. In this way, he had tasted the empowerment of dealing for cash. Brass rods were the prevailing currency, or cowrie shells, and sometimes he may even have seen deutschmarks. He bought some steel hooks and one spool of manufactured line, which had come all the way from Marseille. The line was disappointing. The hooks were excellent. Once he had floated downstream as far as the confluence with the Sangha, a much larger river, powerful, twice as wide as the Ngoko, and had ridden its current for a day—a heady and fearful experience. On the right bank he had seen a town, which he knew to be Ouesso, vast and notorious; he gave it a wide berth, holding himself at midriver until he was past. At day’s end he stopped and slept on the bank; the next day he reversed, having tested himself enough. It took him four days of anxious effort to paddle back up, hugging the bank (except again at Ouesso), climbing through eddies, but the Voyager made it, relieved when he regained his own world, the little Ngoko River, and swollen with new confidence by the time he beached at his camp. This might have occurred, let’s say, in the long dry season of 1916.