Scientists estimate that there is a minimum of 320,000 viruses in mammals awaiting discovery.

To address the challenges of describing and estimating virodiversity, a team of investigators from CII and EcoHealth Alliance began in jungles of Bangladesh—home to the flying fox.  These bats are the largest flying mammal with a wingspan of up to 6 feet; they are also the source of several outbreaks of Nipah virus. The team collected 1,897 biological samples from the animals, which were captured and released. Back in the lab, they used polymerase chain reaction to identify 55 viruses in nine viral families. Of these, only five were previously known, including two human bocaviruses, an avian adenovirus, a human/bovine betacoronavirus, and an avian gammacoronavirus. Another 50 were newly discovered, including 10 in the same family as Nipah. Next the researchers adapted a statistical technique from the field of ecology to estimate that there were another three rare viruses unaccounted for in the samples, upping the estimate of viruses in the flying fox to 58. Finally, this number was extrapolated to all 5,486 known mammals, yielding a total of at least 320,000 viruses.