EEHV in Asian elephants: Evidence of high seroprevalence in Thailand

Elephant endotheliotropic herpesviruses (EEHV) can cause an acute highly fatal hemorrhagic disease in young Asian elephants (Elephas maximus), both ex situ and in situ. Amongst eight EEHV types described so far, type 1 (subtype 1A and 1B) is the most common and virulent. Little is known about routes of infection and pathogenesis. Likewise, knowledge of disease prevalence, especially in range countries, is poor. A large cross sectional serological survey using an EEHV1A glycoprotein B protein antigen specific ELISA, was conducted in camp elephants (n= 994) throughout Thailand. The results were combined with risk factors potentially related to EEHV infection, like elephant age, sex, and geographical location of camps, elephant density, and season. Results indicated a seroprevalence of 42.3%, with 420 of 994 elephants testing positive. Univariable regression analysis identified management system (extensive versus intensive) and region as potential risk factors for the presence of EEHV antibodies, with region being significant in the final multivariable regression model. Prevalence was highest in the North region of the country (49.4%). This study produced baseline serological data for captive elephants throughout Thailand, and found a potentially significant EEHV burden in the population. Thus, there is a high likelihood the disease will continue to be maintained in the captive population, which could potentially threaten wild elephants, although there is the possibility that they too have been exposed to EEHV.