https://en.wikipedia.org/wiki/Elephant_endotheliotropic_herpesvirus

can cause a highly fatal hemorrhagic disease when transmitted to young Asian elephants… generally benign in African elephants… kills up to 80% of severely affected individuals. The disease can be treated with the rapid application of antiviral drugs, but this has only been effective in around a third of cases… Since 1995, there have been over fifty documented disease cases in North America and Europe, of which only nine have been successfully cured.