The EEHVs are members of the Proboscivirus genus, a novel clade most closely related to the mammalian betaherpesviruses that have been responsible for as many as 70 deaths of both zoo and wild Asian elephants worldwide, especially in young calves.[2][3] There are currently six known species/types of the probosciviruses, and the most commonly encountered and most pathogenic form EEHV1 also has two chimeric subtypes, 1A and 1B.,[2][4][5][6][7] as well as numerous distinct strains.[8]