Ebola: The Natural and Human History of a Deadly Virus

by David Quammen

  Joosten’s husband, later her widower, was a fair-skinned man named Jaap Taal, a calm fellow with a shaved head and dark, roundish glasses. Most of the other travellers didn’t fancy this offering, Jaap Taal told me, over a cup of coffee at a café in southwestern Montana. Never mind, for the moment, why he turned up there. Python Cave had been an add-on, he explained, price not included in their Uganda package. “But Astrid and I always said, maybe you come here only once in your life, and you have to do everything you can.” They rode to Maramagambo Forest and then walked a mile or so, gradually ascending, to a small pond. Nearby, half-concealed by moss and other greenery, like a crocodile’s eye barely surfaced, was a low dark opening. Joosten and Taal, with their guide and one other client, climbed down into the cave.

  The footing was bad: rocky, uneven, slick with bat guano. The smell was bad too: fruity and sour. Think of a dreary barroom, closed and empty, with beer on the floor at 3 a.m. The cave seemed to have been carved by a creek, or at least to have channeled its waters, and part of the overhead rock had collapsed, leaving a floor of boulders and coarse rubble, a moonscape, coated with guano like a heavy layer of vanilla icing. The ceiling was thick with bats, big ones, many thousands of them, agitated and chittering at the presence of human intruders, shifting position, some dropping free to fly and then settling again. Astrid and Jaap kept their heads low and watched their steps, trying not to slip, ready to put a hand down if needed. “I think that’s how Astrid got infected,” he told me. “I think she put her hand on a piece of rock, which contained droppings of a bat, which were infected. And so she had it on her hand.” Maybe she touched her face an hour later, or put a piece of candy in her mouth, or something such, “and that’s how I think the infection got in her.”

  Python Cave, in Maramagambo Forest, is just thirty miles west of Kitaka Cave. It too harbors Egyptian fruit bats. Thirty miles isn’t far and individuals from the Kitaka aggregation are quite capable—as the CDC’s mark-recapture study would later prove—of finding their way to roost at Python.

  No one had warned Joosten and Taal about the potential hazards of an African bat cave. They knew nothing of Marburg virus, though they had heard of Ebola. They only stayed in the cave about ten minutes. They saw a python, large and torpid. Then they left, continued their Uganda vacation, visited the mountain gorillas, did a boat trip, and flew back to Amsterdam. Thirteen days after the cave visit, home in North Brabant, Astrid Joosten fell sick.

  At first it seemed no worse than flu. Then her temperature went higher and higher. After a few days, she began suffering organ failure. Her doctors, knowing her case history, with recent time in Africa, suspected Lassa virus or maybe Marburg. Marburg, said Jaap, what’s that? Astrid’s brother looked it up on Wikipedia and told him: Marburg, it kills, could be bad trouble. The doctors moved her to a hospital in Leiden, where she could get better care and be isolated from other patients. There she developed a rash and conjunctivitis; she hemorrhaged. She was put into an induced coma, a move dictated by the need to dose her more aggressively with antiviral medicine. Before she lost consciousness, though not long before, Jaap went back into the isolation room, kissed her, and told her, “Well, we’ll see you in a few days.” Blood samples, sent to a lab in Hamburg, confirmed the diagnosis: Marburg. She worsened. As her organs shut down, she lacked for oxygen to the brain, she suffered cerebral edema, and before long Astrid Joosten was declared brain dead. “They kept her alive for a few more hours, until the family arrived,” Jaap told me. “Then they pulled the plug out and she died within a few minutes.”

  The doctors, appalled by his recklessness in kissing her goodbye, prepared an isolation room for Jaap himself, but it was never needed. “There’s so much they don’t know about Marburg and those other viral infections,” he said to me. Then, still a venturesome traveler, he went off on a snow tour of Yellowstone National Park.

  19

  NEWS OF THE Joosten case reverberated at the CDC. She was the first person known to have left Africa with an active filovirus infection and died. Soon afterward, in August 2008, another team was dispatched to Uganda, this time including the veterinary microbiologist Tom Ksiazek, a veteran of field responses against zoonotic outbreaks, as well as Towner and Amman. Bob Swanepoel and Alan Kemp were again mustered from South Africa. “We got the call, ‘Go investigate,’” Amman told me. Their mission now was to sample bats at Python Cave, where this Dutch woman (unnamed in the epidemiological traffic) had become infected. Her death, her case history, implied a change in the potential scope of the situation. That local Ugandans were dying of the infection was a severe and sufficient concern—sufficient to bring a response team in haste from Atlanta and Johannesburg. But if tourists too were involved, were tripping in and out of some lovely python-infested Marburg repository, in Tevas and hiking boots, blithe, unprotected, and then boarding their return flights to other continents, the place was not just a peril for Ugandan miners and their families. It was also an international threat.

  The team converged at Entebbe and drove southwest. They walked the same trail that Joosten and Taal had walked, to the same crocodile-eye opening amid the forest vegetation. Then, unlike any tourists, they donned their Tyvek pajamas, their rubber boots, their respirators, and their goggles. This time, with cobras in mind, they added snake chaps. Then they went in. Bats were everywhere overhead; guano was everywhere underfoot. In fact, the rain of guano seemed to come so continuously, Amman told me, that if you left something on the floor it would be covered within days. The pythons were indolent and shy, as well-fed snakes tend to be. One of them, by Amman’s estimate, stretched about twenty feet long. The black forest cobras (yes, more of them here too) kept to the deeper recesses, away from heavy traffic. Towner was gazing at a python when Amman noticed something glittery on the floor.

  At first glance it looked like a bleached vertebra, lying in the excremental glop. Amman picked the thing up.

  It wasn’t a vertebra. It was a string of aluminum beads with a number attached. More specifically, it was one of the beaded collars that he and Towner had placed on captured bats at Kitaka Cave, the other Marburg cave, three months earlier and thirty miles away. The code tag spoke one simple fact: Here was collar K-31, from the thirty-first animal they had released. “And of course, I just lost my mind,” Amman told me. “I was, ‘Yeah!’ and jumping around. Jon and I were so excited.” Amman’s insane jubilance was in fact just the sane, giddy thrill that a scientist feels when two small bits of hard-won data click together and yield an epiphany. Towner got it and shared it. Picture two guys in a dark stone room, wearing headlamps, high-fiving in nitrile gloves.

  Retrieving the collar at Python Cave vindicated, in a stroke, their mark-recapture study. “It confirmed my suspicions that these bats are moving,” Amman said—and moving not only through the forest but from one roosting site to another. Travel of individual bats (such as K-31) between far-flung roosts (such as Kitaka and Python) implied circumstances whereby Marburg virus might ultimately be transmitted all across Africa, from one bat encampment to another. It suggested opportunities for infecting or re-infecting bat populations in sequence, like a string of blinking Christmas lights. It voided the comforting assumption that this virus is strictly localized. And it highlighted the complementary question: Why don’t outbreaks of Marburg virus disease happen more often?

  Marburg is only one disease to which that question applies. Why not more SARS? Why not more Nipah? Why not more Ebola? If bats are so abundant and diverse and mobile, and zoonotic viruses so common within them, why don’t those viruses spill into humans and take hold more frequently? Is there some mystical umbrella that protects us? Or is it fool’s luck?

  20

  ALTHOUGH I HAVE lumped Ebola virus provisionally, along with Marburg and SARS coronavirus and Nipah and others, among viruses for which bats serve as reservoirs, I want to re-emphasize: That inclusion is tentative. It’s a hypothesis awaiting assessment against further evidence. No one, as of this writing, h
as isolated any live ebolavirus from a bat—and virus isolation is still the gold standard for identifying a reservoir. That may happen soon; people are trying. Meanwhile the Ebola-in-bats hypothesis seems stronger since Jonathan Towner’s team achieved their isolations of Marburg virus, so closely related, also from bats. And it has been strengthened further, at least a little, by another bit of data added to the ebolavirus dossier about the same time. This bit came in the form of a story about a little girl.

  Eric Leroy, after having chased the secrets of Ebola for more than a decade, led the team that reconstructed this girl’s story. Their new evidence derived not from molecular virology but from old-fashioned epidemiological detective work—interviewing survivors, tracing contacts, discerning patterns. The context was an outbreak of Ebola virus that occurred in and around a village called Luebo, along the Lulua River, in a southern province of the Democratic Republic of the Congo. Between late May and November 2007, at least 264 people sickened with what seemed to be or (in some confirmed cases) definitely was Ebola virus. Most of them died. The lethality was 70 percent. Leroy and his colleagues arrived in October, as part of an international WHO response team in cooperation with the DRC’s Ministry of Health. Leroy’s study focused on the network of transmissions, which all seemed traceable to a certain 55-year-old woman. She became known, in their report, as patient A. She wasn’t necessarily the first human to get infected; she was merely the first identified. This woman, elderly by Congo village standards, had died after suffering high fever, vomiting, diarrhea, and hemorrhages. Eleven of her close contacts, mainly family, who had helped care for her, sickened and died too. The outbreak spread onward from there.

  Leroy and his group wondered how the woman herself had gotten infected. No one in her village had shown symptoms before she did. So the investigators broadened their search to surrounding villages, of which there were quite a few, both along the river and in the forest nearby. From their interviews and their legwork, they learned that the villages were interconnected by footpaths, and that on Mondays the heavy traffic led to one particular village, Mombo Mounene 2, the site of a big weekly market. They also learned about an annual aggregation of migrating bats.

  The bats generally arrived in April and May, stopping over amid a longer journey, finding roost sites and wild fruit trees on two islands in the river. In an average year, there might be thousands or tens of thousands of animals, according to what Leroy’s group heard. In 2007, the migration was especially large. From their island roosts, the bats ranged the area. Sometimes they fed at a palm oil plantation along the river’s north bank; the plantation was a leftover from colonial times, now abandoned and gone derelict, but still offering palm fruits in April on its remaining trees. Many or most of the animals were hammer-headed bats and Franquet’s epauletted fruit bats (Epomops franqueti), two of the three in which Leroy had earlier found Ebola antibodies. While roosting, the bats dangled thickly on tree branches. Local people, hungry for protein or a little extra cash, hunted them with guns. Hammer-headed bats, big and meaty, were especially prized. A single shotgun blast could bring down several dozen bats. Many of those animals ended up, freshly killed, raw and bloody, in the weekly market at Mombo Mounene 2, from which buyers carried them home for dinner.

  One man who regularly walked from his own village to the market, and often bought bats, seems to have suffered a mild case of Ebola. The investigators eventually labeled him patient C. He wasn’t a bat hunter himself; he was a retail consumer. During late May or early June, according to patient C’s own recollection, he weathered some minor symptoms, mainly fever and headache. He recovered, but that wasn’t the end of it. “Patient C was the father of a 4-year-old girl (patient B),” Leroy and his team later reported, “who suddenly fell ill on 12 June and died on 16 June 2007, having had vomiting, diarrhoea, and high fever.”27 The little girl didn’t hemorrhage, and she was never tested for Ebola, but it’s the most plausible diagnosis.

  How had she contracted it? Possibly she had shared in eating a fruit bat that carried the virus. What are the odds faced by bat-eaters? Hard to say; hard even to guess. If the hammer-headed bat is an Ebola reservoir, what’s the prevalence of the virus within a given population? That’s another unknown. Towner’s group found 5 percent prevalence of Marburg in Egyptian fruit bats, meaning that one animal in twenty could be infected. Assuming a roughly similar prevalence in the hammer-headed bat, the little girl’s family had been unlucky as well as hungry. They might have eaten nineteen other bats and gotten no exposure. Then again, if a bat meal was shared, why didn’t the girl’s mother and other family members get sick? Possibly her father, infected or besmeared after purchasing bats in the market, had carried the girl (common practice with small children thereabouts) along the footpath back to their village. The father, patient C, seems to have passed the virus to nobody else.

  But his little daughter did pass it along. Her dead body was washed for burial, in accord with local traditions, by a close friend of the family. That friend was the 55-year-old woman who became patient A.

  “Thus, virus transmission may have occurred when patient A prepared the corpse for burial ceremony,” Leroy’s group wrote.28 “When interviewed, the two other preparers, the girl’s mother and grandmother, reported they did not have direct contact with the corpse and they did not develop any clinical sign of infection in the four following weeks.” Their role in the funerary washing was apparently observational. They didn’t touch the dead body of their daughter and granddaughter. But patient A did, performing faithfully the service of a close family friend, after which she went back to her life—what was left of it. She resumed her social interactions, for a time, and eventually 184 other people caught Ebola and died.

  Leroy’s team reconstructed this story and then, keen to extract meaning, asked themselves several questions. Why had the father infected his daughter but no one else? Maybe because he had a mild case, with a low level of virus in his body and not much leaking out. But if his case was mild, why was his daughter’s so severe, killing her within four days? Maybe because, as a small child racked with vomiting and diarrhea, she had died of untreated dehydration. Why was there only one bat-to-human spillover event? Why was patient C unique, as the sole case linked directly to the reservoir? Well, maybe he wasn’t. He was just the only one that came to notice. “In fact, it is highly likely that several other persons were infected by bats,” Leroy’s group wrote, “but the circumstances required for subsequent human-to-human transmission were not present.”29 They were alluding to dead-end infections. A person sickens, suffers solitarily or with carefully distanced succor from wary family or friends (food and water left at the door of a hut), and dies. Is buried unceremoniously. Eric Leroy didn’t know how many unfortunate people in the Luebo area may have eaten a bat, touched a bat, become infected with Ebola virus, succumbed to it, and been dropped into a hole, having infected no one else. Amid the horrific confusion of the outbreak, in those remote villages, the number of such dead-end cases might have been sizable.

  This brought Leroy’s team to the pivotal question. If the circumstances required for human-to-human transmission hadn’t been met, what were those circumstances? Why hadn’t the Luebo outbreak gone really big? Why hadn’t the tinder ignited the logs? It had started in May, after all, and the WHO didn’t get there until October.

  Whatever circumstances had combined to constrain the Luebo outbreak to a “mere” 264 cases and 186 fatalities, those circumstances would not be present during the West African outbreak of 2014.

  21

  THIS BRINGS ME back to that fruitless stakeout near Moba Bai, in the Republic of the Congo, in October 2006. It brings me back to the shared fates of people and apes.

  After our days of searching the bai complex for gorillas, and finding virtually none. Billy Karesh and I and the expert gorilla tracker Prosper Balo, along with other members of the team, traveled three hours back down the Mambili River by pirogue. We carried no samples of frozen gorilla b
lood, but I was nevertheless glad to have had the chance to come looking. From the lower Mambili we turned upstream on one of its branches, motored to a landing, and then drove a dirt road to the town of Mbomo, central to the area where Ebola virus had killed 128 people during the 2002–2003 outbreak.

  Mbomo is where the medical anthropologist Barry Hewlett, arriving just after four teachers were hacked to death, had encountered murderous suspicions between one resident and another that the Ebola deaths resulted from sorcery. We stopped at a little hospital there, a U-shaped arrangement of low concrete structures surrounding a dirt courtyard, like a barebones motel. Each of the rooms, tiny and cell-like, gave directly onto the courtyard through a louvered door. As we stood in the heat, Alain Ondzie told me that Mbomo’s presiding physician, Dr. Catherine Atsangandako, had famously locked an Ebola patient into one of those cells just a year earlier, supplying him with food and water through the slats. The man was a hunter, presumably infected by handling one form or another of wild meat. He had died behind his louvered door, a lonely end, but the doctor’s draconian quarantine was generally credited with having prevented a wider outbreak.

  Dr. Catherine herself was out of town today. The only evidence of her firm hand was a sign, painted in stark red letters: