Fruit bats carry the Nipah virus, which can be transmitted to humans and cause severe disease. In Bangladesh, the virus causes a disease outbreak almost every year. Dr. Jon Epstein of the EcoHealth Alliance explains the evidence that revealed bats are the natural reservoir of the virus. Their research also shows the route of transmission to humans. Dr. Epstein and collaborators in Bangladesh are now monitoring bat populations throughout the country for the presence of the virus to identify human populations that might be at risk of transmission.