Imagine if pandemics could be forecast by infectious disease scientists the way that bad weather can be tracked by meteorologists. New viruses would still infect people, but the cost of monitoring the emergence of those novel pathogens would be far less than the expense of dealing with a worldwide outbreak. At least that’s the reasoning behind a new study, published today in mBio, in which researchers propose launching a billion-dollar-plus global surveillance plan to find all the viruses lurking in mammalian wildlife before those same viruses find us.
A consortium of scientists, funded by the US Agency for International Development (USAID), headquartered in Washington, DC, estimated that at least 320,000 viruses remain unidentified in the world’s 5,500 mammals. They argue that the cost of systematically searching for those new viruses would pale in comparison to the estimated $16 billion another epidemic such as SARS could cost.
That epidemic, which started in China in 2003 after a coronavirus carried by bats and palm civets started infecting humans, eventually killed more than 700 people and spread to 37 countries worldwide. The ongoing outbreak of Middle East respiratory syndrome (MERS) hasn’t yet reached such pandemic levels. But with 108 laboratory-confirmed cases of infection in nine countries, including 50 deaths, public health officials remain on high alert.
Eric Delwart, a virologist at the Blood Systems Research Institute in San Francisco who was not involved in the study, describes the virus-hunting proposal as “a feasible approach” to looking for zoonotic diseases that animals could transmit to humans. “This study provides one of the first data-based estimates of the scope of the viro-diversity which humans and their livestock have to face and from which the next viral epidemic will emerge,” he says. “Although other people have looked at pathogen levels before and estimated that there are two new human viruses coming each year, we don’t know where they’re coming from.”
The study authors based their estimates on the study of a flying fox bat, Pteropus giganteus, which is known to harbor the Nipah virus and cause annual outbreaks among people in Bangladesh. Under the auspices of a USAID project called PREDICT, program co-director Jonna Mazet and her colleagues sequenced DNA extracted from more than 7,000 samples of urine, throat swabs and stool from the bats. Their analysis turned up 55 viruses, of which only five were previously known to science. Mazet and her colleagues extrapolated from those results to calculate that at least 320,000 viruses probably remain to be found in other understudied mammals.
It cost about $1.2 million for the PREDICT researchers to find, prepare and analyze all the flying fox bat samples from Bangladesh, a location that the scientists note is probably one of the less expensive places to go virus hunting. Costs could climb much higher if they looked in more remote areas for animals that are harder to track and handle. The researchers figure that fully cataloguing all the mammal-infecting viral diversity out there would cost about $6.3 billion spread over a 10-year period. However, trying to find just 85% of unknown viruses would be much cheaper — perhaps only $1.4 billion over the next decade. “We don’t need to find all of them,” says Mazet, an epidemiologist at the University of California–Davis School of Veterinary Medicine.
It isn’t clear who would fund such a surveillance system, especially with the USAID funding for the PREDICT project — just $15 million per year — slated to end in September 2014. However, Mazet is hopeful that findings from similar studies will draw new funding sources to continue the work.
Image from © 2013 Jonathan H. Epstein/EcoHealth Alliance