The proboscivirus genus: Hemorrhagic disease caused by elephant endotheliotropic herpesviruses

A decade ago, Richman et al.1 reported in Science about an unusual acute hemorrhagic disease in Asian elephant calves that was associated with systemic infection by a novel herpesvirus named elephant endotheliotropic herpesvirus (EEHV). Since then, there have been many additional confirmed cases of this disease and many more species of elephant herpesviruses have been discovered. Overall, the disease has afflicted 20% of all live captive-born Asian elephant calves in North American and European zoos with a very high mortality rate, and has been responsible for two-thirds of all deaths of juvenile Asian elephants in captivity in North America. The disseminated form of the disease appears to represent primary infection of naïve animals, and has a very rapid onset with initial clinical symptoms of lethargy and edema, followed by focal hemorrhaging in all major organs and death within 1 to 5 days. High virus loads are found in the PBMC and serum with evidence for lytic infection targeted to microvascular endothelial cells, where typical Cowdrey-like nuclear inclusion bodies are observed. Overall, more than 50 cases, mostly in Asian calves between the ages of one and eight years of age, have been identified in American and European zoos, including several adults and up to three African elephant calves as well. Nine calves have survived after early aggressive anti-herpesvirus drug treatment with famciclovir or ganciclovir, but this same medication was not sufficient to save many others. Furthermore, as many as 18 recent deaths of orphan and wild Asian elephant calves in four different countries in Asia have also been attributed to EEHV.