Mammals may host 320,000 undiscovered viruses, says study

US researchers said there is a minimum of 320,000 viruses in mammals alone awaiting discovery, all with the potential to affect humans.

It is estimated that about 70 percent of emerging viral diseases such as HIV/AIDS, West Nile, Ebola, SARS, and influenza are zoonoses - animal infections that spread into humans. Yet until now, there has been no good estimate of the actual number of viruses that exist in any wildlife species, Xinhua reported Tuesday.

"Historically, our whole approach to discovery has been altogether too random," said lead author Simon Anthony of the Center for Infection and Immunity at the 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. But the pool of all viruses in wildlife, including many potential threats to humans, is actually much deeper."

In a study published in the journal mBio, researchers analysed 1,897 samples collected from flying fox bats in the jungles of Bangladesh, which are the largest flying mammal with a wingspan of up to 6 feet (about 1.8 meters) and source of several outbreaks of deadly Nipah virus.

They identified 55 viruses in nine viral families only five of which were previously known. Another 50 were newly discovered, including 10 in the same family as Nipah.

The researchers also estimated that there were three other rare viruses unaccounted for in the samples, raising the estimate of viruses in the flying fox to 58.

They then extrapolated their data to include all 5,486 known mammals and calculated that there are at least 320,000 new viruses.

Based on the cost of collecting their data on the flying fox bats, the researchers said the cost of surveillance, sampling and identifying of viruses in all mammals would reach $6.3 billion.

Given the disproportionate cost of discovering rare viruses, they showed that limiting discovery to 85 percent of estimated viral diversity would bring the cost down to $1.4 billion.

"By contrast, the economic impact of the SARS pandemic is calculated to be $16 billion," said Anthony.

"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 by facilitating better surveillance and rapid diagnostic testing.

"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.

The researchers said the initial estimate of 320,000 is just a starting point and it will likely be considerably higher after taking into account additional viral families and employing high throughput sequencing methods.