Deep In The Rain Forest, Stalking The Next Pandemic
Tuesday, October 21st, 2008
For Nathan Wolfe, a 38-year-old visiting professor at Stanford, an ordinary workday can look like a clip from “Survivor” — chasing primate hunters through the dense foliage of rural Cameroon, sloshing through mud and streams, dodging branches and malaria-carrying mosquitoes.
Dr. Wolfe says he enjoys the adventure. But he has a broader purpose: staving off global pandemics before they happen.
The subsistence, or “bushmeat,” hunters he tracks face a singular occupational hazard: their blood often mingles with that of their prey. Because animals like chimpanzees and orangutans are genetically similar to humans, the likelihood of virus transmission between species is very high.
Both H.I.V. and Ebola, for example, have documented primate origins, and a paper published in Nature in February noted that 60 percent of emerging human pathogens came from animals.
“We’re starting to expand the watershed of global disease control,” Dr. Wolfe said. “Before, the best thing you could do was develop a vaccine, but now people are recognizing that’s not going to be enough.
“If you find diseases before they’ve really emerged,” he continued, “you can control them early on, before you get a major epidemic.”
That pre-emptive-strike approach to epidemic management, he said, is what makes chasing the Cameroonian hunters so crucial.
When he can persuade the hunters, whom he calls “sentinels,” to supply him with blood samples, he can form a better idea of which new animal diseases they are exposed to — and, by extension, which emerging viruses could pose the biggest threat to humans.
Since he began his hunter studies, he has come across several viruses never before seen in humans, including retroviruses from the same family as H.I.V.
“With epidemics, people have been standing on the shore, waiting for the gusher to hit the ocean,” Dr. Wolfe said, referring to the tidal-wave impact a widespread epidemic could have around the world. “But to prevent epidemics, you have to look at the various little sources that feed into the river.”
With the goal of identifying more of these “little sources” — new disease-causing pathogens — and choking them off, Dr. Wolfe started the Global Viral Forecasting Initiative this year. If new disease strains could be culled before they had a chance to take hold in humans, he reasoned, health organizations would have to spend less money and energy on developing expensive vaccines and treatment drugs.
Google’s philanthropic arm, Google.org, is announcing Tuesday that it will contribute $5.5 million to the initiative; that is being matched by $5.5 million from the Skoll Foundation, which supports the work of social entrepreneurs.
“Nathan is going to be a rock star in this field,” said Frank Rijsberman, a Google.org program director. “We have high hopes he’ll discover 5 to 10 new viruses within the next few years.”
While outsiders and colleagues alike have endorsed Dr. Wolfe’s forecasting tactics, putting them into practice is a tall order. After his team arrives in a rural Cameroonian village on a rickety bus, its first task is to convince local populations that the research poses no threat to their way of life.
“People can’t always see a connection between diseases and wild animals,” said Matthew LeBreton, a research coordinator who designs field education programs for the villagers. “And they sometimes think that we’re going to have their meat confiscated. If someone talks to them about bushmeat, that’s what they’re going to hear.”
Once rapport is established, the data collection can begin. Technicians supply the hunters with bits of filter paper, which they use to absorb blood dripping from their prey. At the same time, scientists take blood samples from the hunters themselves. All of the samples are tested for unfamiliar viruses.
“The main things we look for are: Does a particular virus cause disease, and is it transmissible?” Dr. Wolfe said. “We know there are certain types of viruses that are nasty — influenza, for instance, is an area that is not a blindside. But a lot of viruses have come out of nowhere, like H.I.V., or to a certain extent SARS. Because we know we have the potential to be blindsided, we really have to investigate the unknowns.”
To map the emergence of novel viruses, Dr. Wolfe and his colleagues in the Global Viral Forecasting Initiative — more than 100 scientists in nine countries — have begun following other sentinel populations, like people who receive frequent blood transfusions. They have recently expanded their investigations of viruses that cross the animal-human barrier, conducting research in field locations in China, Madagascar, Malaysia and Paraguay.
Thanks to new techniques for sequencing DNA in the viruses they find, epidemiologists can quickly identify the most virulent new pathogens — the ones that have high mutation rates or lend themselves to recombination, in which strands of DNA are broken and then joined to other genetic material. A new variant of influenza, for instance, could be dangerous, but it could cause epidemics only if it were genetically capable of staying one step ahead of the immune system’s defenses.
Tracking the viral mix in a given population over time is also critical, said Forest Rohwer, a microbiologist at San Diego State University who works with Dr. Wolfe.
“Imagine you’re doing routine monitoring of an area,” Dr. Rohwer said. “If you take 100 different blood samples a day to look at the viruses in those 100 samples, and at some point you see a shift away from what you normally see in that system, then you can say, ‘O.K., there’s something wrong here; let’s look at it in depth.’ ”
Once a harmful virus has been located, the next step is to determine how quickly it can spread. Dr. Wolfe’s colleagues and other scientists have developed computer simulations that can be customized to take account of population size and density, family size and transportation patterns.
“You create a population of individuals and then make the rules for how they move around based on your data,” said Dr. Donald S. Burke, dean of the University of Pittsburgh’s Graduate School of Public Health, who helped create some of these simulations. “It’s like SimEpi.”
The simulation then predicts how a virus with a given set of transmissibility properties will thrive in a particular environment. Once Dr. Wolfe and his colleagues isolate a new virus or variant that seems to be spreading in a small area, they can zero in on its primary characteristics — the likelihood that a sick person will infect someone else, for instance — and feed the data into the simulation to generate an idea of how the virus could spread.
The results offer a rough but valuable estimate of how and where a nascent epidemic could take hold. So far, simulations show that for all but the most virulent new pathogens, there is “a reasonable combination of policy options well within the range of the health authorities that, if prepared in advance and implemented quickly, could stop a global disaster,” Dr. Burke said, adding, “If that’s the case, then by God, we better get ready.”
Dr. Wolfe acknowledges that the task of preparing for the next pandemic is gargantuan — far too big for his team alone.
“What we’re doing is our best guess on the ideal way to create an early warning system, but there are going to be 20 or 30 different approaches tried,” he said. “The field of pandemic prevention will become huge over the next few years, funded on the order of billions of dollars. It’s going to be a new movement.”
Source — The New York Times