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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.