There could be at least 320,000 viruses awaiting discovery that are circulating in animals, a study suggests. Researchers say that identifying these viral diseases, especially those that can spread to humans, could help to prevent future pandemics.
The team estimates that this could cost more than £4bn ($6bn), but says this is a fraction of the cost of dealing with a major pandemic.
Prof Ian Lipkin, director of the Center for Infection and Immunity at Columbia University's Mailman School of Public Health in the US, said: "What we're really talking about is defining the full range of diversity of viruses within mammals, and our intent is that as we get more information we will be able to understand the principles that underlie determinants of risks."
Nearly 70% of viruses that infect humans, such as HIV, Ebola and the new Middle East Respiratory Syndrome (Mers), originate in wildlife.
But until now, the scale of the problem has been difficult to assess.