Mostly empty tables at a cafe in Toronto, Canada during a 2003 SARS outbreak. The economic impact of SARS on Toronto tourism was evident as pedestrian traffic was low at Harbourfront, usually a hub of activity on sunny weekends. (File//Christine Chew/UPI) | License Photo

The first estimate of the total viral diversity in mammals is possibly finite, and much lower than previously thought, at just 320,000 viruses in mammals awaiting discovery.

Nearly 70 percent of emerging viral diseases including HIV/AIDS, West Nile, Ebola, SARS and influenza are zoonoses -- animal infections that cross into humans.


"Historically, our whole approach to discovery has been altogether too random," said lead author Simon Anthony of the Center for Infection and Immunity (CII) at Columbia University's Mailman School of Public Health.

"What we currently know about viruses is very much biased towards those that have already spilled over into humans or animals and emerged as diseases," Anthony said.

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Researchers used 1,897 flying fox samples -- the largest flying mammal with a wingspan of up to six feet, and the source of outbreaks of the Nipah virus -- and found 55 viruses in nine viral families, only five of which were previously known. Estimating an additional 3 undetected rare viruses, that total was extrapolated to all 5,486 known mammals.

Scientists estimate that collecting evidence of these viruses would cost approximately $6.3 billion, or just $1.4 billion if limited to 85 percent of total viral diversity, due to the outsized cost of discovering extremely rare viruses.

By contrast, the SARS pandemic had an estimated economic impact of $16 billion.

"We're not saying that this undertaking would prevent another outbreak like SARS. Nonetheless, what we learn from exploring global viral diversity could mitigate outbreaks," Anthony said.

"If we know what's out there, we'll be a lot better prepared when a virus jumps over into a human population," Anthony said.

"To quote Benjamin Franklin, an ounce of prevention is worth a pound of cure," said senior author and CII Director W. Ian Lipkin. Developing reliable, rapid diagnostics and antivirals takes time, and the authors note it is better to spend that time before an outbreak in the human population.

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Scientists say 320,000 is a starting estimate, and as viral families are sequenced that number could rise. Currently, large-scale zoonotic virus discovery is being undertaken by the PREDICT Project, funded by the United States Agency for International Development (USAID).

But so far PREDICT has only discovered some 240 novel viruses worldwide, including new coronaviruses, like the ones that cause SARS and the new Middle East Respiratory Syndrome.