sciencehabit writes: Ebola, HIV, influenza, MERS. Plenty of animal viruses cause devastating diseases in humans. But nature might have many more in store. In a new study, U.S. researchers estimate that there are more than 320,000 unknown viruses lurking in mammals alone. One of them could touch off the next pandemic if it jumps to humans, says Nathan Wolfe, a virologist who was not involved in the work and founder and CEO of Metabiota, a company that contracts with governments and health agencies to track disease outbreaks. "This paper gives an idea of what's actually out there."