NOUABALE-NDOKI NATIONAL PARK, Congo Republic — More than 3,000 miles from the fading Ebola crisis in West Africa, a team of U.S.-funded researchers is hunting deep in a remote rain forest for the next outbreak.
They aren’t looking for infected people. They’re trying to solve one of science’s great mysteries: Where does Ebola hide between human epidemics?
The answer appears to lie in places such as this — vast tracts of African jungle where gorillas, bats and other animals suspected of spreading the virus share a shrinking ecosystem. If scientists can pinpoint the carriers, and how Ebola is transmitted between them, future epidemics will be easier to anticipate — or even prevent.
The mission is urgent. Based on the pattern of previous outbreaks, the next one probably isn’t far away.
The world was shocked by the most recent epidemic, which has killed more than 10,000 people in Guinea, Liberia and Sierra Leone. But it was hardly the first. Over the past 40 years, Ebola has exploded sporadically in sub-Saharan Africa, wiping out scores of people. It has also quietly decimated wildlife populations. As many as a third of the world’s gorillas have died of the disease.
Scientists are more anxious than ever to figure out why the virus has flared in some places but not others. And so, on a recent humid Sunday morning, a 51-year-old wildlife veterinarian from Michigan loaded his gear into a leaky dugout canoe and headed with his team into the Congo River Basin.
They swatted away swarms of flies and bees as they paddled to the end of the river and then trekked for miles through the brush. They were seeking one of the animals suspected of harboring Ebola: the red river hog.
If the researchers captured one of the wild pigs and it tested positive for Ebola, it would confirm decades of hypotheses and help scientists start to map the disease. It would also be a frightening prospect — a sign that the virus was again ready to pounce on a human population.
Kenneth Cameron, a compact, energetic man who works for the New York-based Wildlife Conservation Society, had spent much of his life quietly pursuing Ebola through Central Africa. But this time, the wildlife veterinarian was getting calls from big government agencies. The National Institutes of Health had expressed interest in supporting his work if things went well.
“The West Africa outbreak was a reminder to everyone that it’s out there — and it’s waiting to emerge again,” he said.
There have been 24 recorded outbreaks of Ebola since 1976, when it was first identified. Each began with an interaction between a human and an animal. One was believed to have started with a man hunting and butchering an infected gorilla, another with a family eating the carcass of a chimpanzee. Those events are called “spillovers.”
In West Africa, the recent Ebola outbreak probably began with a 2-year-old Guinean boy who touched a droplet of bat feces in December 2013.
“It’s only a question of how destructive the next one will be,” said Cameron, whose research is funded by the U.S. Fish and Wildlife Service.
Ebola remains one of the least understood of the world’s deadly diseases. Scientists suspect that fruit bats are the “reservoir host” of the virus, meaning they carry and transmit the disease but don’t suffer from it themselves. But even that hasn’t been proven.
Many diseases, such as rabies and influenza, are also transmitted between humans and animals. But in most cases, we know which species are susceptible. That’s not true with Ebola. In October, for example, the city of Dallas spent $27,000 to quarantine the dog of an Ebola-infected nurse. Can dogs transmit the disease? No one knows.
Here’s what is known. In 2002, in a village called Mbomo, more than 200 miles from where Cameron’s team was working, people started getting sick. At first, the villagers assumed it was a particularly vicious strain of malaria. But then the ill tested positive for Ebola. Over several weeks, 178 people died.
When the epidemiologists traced the disease, they heard the story of hunters who had cooked and eaten the carcass of a gorilla found in the jungle. At the time, dozens of gorillas had died suddenly.
“Soon everyone understood that it came from the forest,” recalled Marco Joel, who was the director of the local Red Cross chapter at the time. “The hunters brought it back and infected their families.”
For years, the world’s gorillas had been dying of Ebola in staggering numbers. By 2007, largely because of Ebola outbreaks, the International Union for Conservation of Nature deemed western lowland gorillas to be “critically endangered.”
“You can’t separate public health from animal health there. It’s all one issue,” said Vincent Munster, the head of the virus ecology unit at NIH’s Montana-based Rocky Mountain Laboratories.
In November 2003, people in Mbomo started getting sick again. The doctors returned. The Ebola tests came back positive. Dozens more died. But in trying to trace this outbreak, epidemiologists heard a different story. A group of hunters had killed and eaten a wild pig days before falling ill.
Was this outbreak connected to the last — a pig that had become infected by a gorilla? Or was this a separate transmission chain entirely? No one could tell. No pigs had ever tested positive for Ebola.
Twelve years later, under a towering ficus tree in the jungle, Cameron and his team hammered the posts of a metal cage into the ground. They set up a trap door that would be triggered by the weight of the animal, which would be tranquilized and examined for the virus.
Cameron watched as the trap door was tested for the first time. The stakes were high. If he couldn’t capture a pig, it would make it hard to secure funding for a follow-up study. The door went down with a bang.
“Ça marche!” Cameron screamed in French with boyish excitement. “It works.”
Since 2005, as part of his Ebola research, Cameron has tested primate carcasses and feces. He has captured bats using large translucent nets. He has darted gorillas with a tranquilizer gun. He has loaded blood samples onto jeeps and boats and planes to be taken to labs and tested for Ebola.
There have been successes, such as when his team found Ebola antibodies in the feces of gorillas, a sign that the animals had been exposed to the disease. But largely, the research has been a slow crawl through the dark.
Part of the difficulty is finding the animals he’s looking for. For every thousand bats his team has captured over the past four years, only one has shown evidence of the virus.
“It’s hugely important work,” said Munster, of NIH. “The more we know about the virus, the more intervention strategies we can create.”
By leaping from species to species, Ebola is doing what all pathogens do — attempting to survive and reproduce. And though scientists aren’t sure which species are immune, they have a pretty good idea of how it’s transmitted between vulnerable animals.
Cameron uses the example of a tree he once recorded with a field video camera in the Congo Republic. Pigs, gorillas and chimpanzees were all filmed eating from it, often consuming different pieces of the same fruit.
“You watch that film and you see just how quickly this thing could spread,” Cameron said, wide-eyed.
In a place like this country’s north, where bush meat is still consumed as a rare source of protein, the chain would almost inevitably lead to humans. It’s a chain that the men on Cameron’s team know well. They are from local villages, and while they know enough to no longer consume wildlife, they still extol its virtues.
“Elephant is delicious,” said Makoti Marcelin, one of the wildlife trackers. “It tastes just like gorilla.”
But while people in the Congo Republic mostly stopped eating great apes in the wake of the 2002 Ebola outbreak, pigs are still sold in markets around the country.
If an infected pig made its way near a town or village, it would almost definitely be eaten. In 2002, the trip between the north and the capital, Brazzaville, took about three days — a likely reason the disease never reached the city. Now, a new Chinese-built road has made the journey much faster. Insulating the next outbreak will be much more difficult.
“The state of preparedness of the country is very low,” said Jean-Vivien Mombouli, the director of research at the country’s National Laboratory for Public Health. “We would not be able to recognize the disease early enough to limit the outbreak to less than 10 cases.”
As researchers work on an Ebola vaccine, many conservationists are pushing for it to be given to animals, too. That would require a massive effort to tranquilize the animals before vaccinating them or disguise the serum in their food. But it could save thousands of the animals.
It could also help prevent another spillover — a possibility that was underscored just before Cameron’s team left for the jungle, when a gorilla attacked a man on a different research team, biting his leg and drawing blood.
The morning after the trap was set, Cameron’s team went back to the area.
“There were pigs here last night,” said another veterinarian, Alain Ondzie, pointing to a trail with hoof marks nearby.
But the metal cage was empty.
“It’s frustrating,” Cameron said. “There’s still just so much we don’t know.”
When he returned to his office in the capital, he e-mailed his headquarters in New York that he hadn’t yet caught any pigs but was hopeful about the next site visit in a few weeks.
A few miles away was one of the city’s largest markets, a frenzy of people selling chicken, antelope and other meat, displayed on wooden tables under buzzing clouds of flies.
In one area, the tables were full of wild pig, brought from the northern Congo Republic, near Cameron’s research site. The salesman said he had heard about Ebola — about the epidemic 3,000 miles away. But there had been no impact on local people’s taste for wild pig.
He looked down at his table.
“We all know that pigs can’t get Ebola,” he said confidently.