Researchers estimate at least 320,000 viruses in the world's mammals

"If we know what's out there, we'll be a lot better prepared when a virus jumps over into a human population," said Dr. Simon Anthony, researcher and lead author of a published study that produced the first estimate of total viruses in mammals - a hefty 320,000.

By quantifying the number of viruses, Anthony and a team of researchers from the Center for Infection and Immunity (CII) at Columbia University's Mailman School of Public Health and EcoHealth Alliance are aiming to build knowledge about discovering and monitoring zoonoses, and ultimately mitigate the damage from viral outbreaks.

CII researchers chose the flying fox - an enormous bat residing in Southern Asia - as the first mammal species from which they would collect and analyze biological samples. The team collected 1,897 samples from the bats, then used polymerase chain reaction to identify 55 viruses in nine viral families, according to the study.

Researchers said that 50 of the 55 viruses found in the flying fox were newly discovered, and they employed a statistical technique to estimate that there were three more rare viruses contained in the samples. Using the total estimate of 58 viruses, the researchers then projected that number across the 5,486 known mammals on the planet, which produced a total virus estimate of about 320,000.

Making sense of the numbers

The estimated number of viruses appears lofty at first glance considering that only approximately 200 zoonoses have been discovered to date, but it actually pales in comparison to much higher numbers that have previously been discussed, said Dr. Peter Daszak, corresponding author and president of EcoHealth Alliance.

“For decades, we've faced the threat of future pandemics without knowing how many viruses are lurking in the environment, in wildlife, waiting to emerge. Finally we have a breakthrough - there aren't millions of unknown virus, just a few hundred thousand, and given the technology we have it's possible that in my lifetime, we'll know the identity of every unknown virus on the planet,” Daszak said.

Using data from the flying fox study, CII researchers were able to estimate the financial cost of discovering all viruses in mammals at $6.3 billion. The sum seems prohibitive until you compare it to the financial fallout from a single large-scale viral outbreak, Anthony said.

"By contrast, the economic impact of the SARS epidemic is calculated to be $16 billion," Anthony said. "We're not saying that this undertaking would prevent another outbreak like SARS. Nonetheless, what we learn from exploring global diversity could mitigate outbreaks by facilitating better surveillance and rapid diagnostic testing."

Researchers estimated that the expense for virus discovery could be lowered to $1.4 billion by discovering only 85 percent of viral diversity, which eliminates the high costs of hunting down extremely rare viruses.

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Read the full study titled A Strategy to Estimate Unknown Viral Diversity in Mammals published in the journal mBio

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