Elephant endotheliotropic herpesviruses (EEHV), also known as Elephantid betaherpesvirus 1 (ElHV-1), are a type of herpesvirus that can lead to a highly fatal hemorrhagic disease when transmitted to young Asian elephants. In African elephants, related forms of these viruses have been found in wild populations, generally causing benign effects and occasionally resulting in small growths or lesions. However, certain types of EEHV can cause a severe and lethal disease in Asian elephants, leading to the death of up to 80% of severely affected individuals. While the disease can be treated with prompt administration of antiviral drugs, this approach has only shown effectiveness in approximately one-third of cases.
The first instance of the fatal form of the disease was documented in 1990, although tissue samples from the 1980s have since tested positive for the virus, and localized skin lesions in wild African elephants were recorded as far back as the 1970s. Since 1995, there have been over fifty recorded cases of the disease in North America and Europe, with only nine of them successfully cured. The majority of affected individuals are young elephants born in captivity, although a small number of older wild-born adults in zoos have also succumbed to the disease. Additionally, cases caused by the same pathogenic type of EEHV have been identified in both orphaned and wild calves in Asian elephant populations.