Longitudinal molecular and serological surveillance of elephant endotheliotropic herpesviruses through relocation in a captive herd of Asian elephants (Elephas maximus)

Background Elephant endotheliotropic herpesviruses (EEHVs) can cause fatal haemorrhagic disease (EEHV-HD) in young Asian elephants ( Elephas maximus ), posing a significant threat to the conservation of the species. Understanding the dynamics of EEHV infection within a herd may help to understand risk factors associated with EEHV-HD, however, only few longitudinal EEHV surveillance studies exist. Methods This study documented EEHV viral dynamics in nine Asian elephants over a two-year period spanning an anticipated major stressor: relocation from Melbourne Zoo to Werribee Open Range Zoo. Antibodies specific to each EEHV (sub)species were measured by enzyme-linked immunosorbent assays (ELISA). Viral DNA was detected in blood and trunk wash samples by quantitative PCR (qPCR). Results Contrary to our hypothesis, EEHV detection by qPCR was more common prior to relocation than after relocation. Pre-relocation viral detection was largely attributable to a series of systemic EEHV5 infections in five elephants, unrelated to any changes in herd management or dynamics. Prospective serological testing demonstrated an increase in EEHV5A-specific antibodies in three young elephants with low pre-existing antibodies in response to systemic EEHV5 infection. Trunk wash detection of virus preceded viraemia in four out of five elephants with systemic EEHV5 infection, including two of the animals with low EEHV5A antibodies, indicating virus exposure or localised replication. Conclusions Transport and relocation of the entire herd were not associated with widespread viral reactivation. In this herd, combined serology testing and trunk wash surveillance identified animals at risk of systemic EEHV infection and provided early evidence of viral exposure prior to viraemia. Integration of serology and trunk wash qPCR with routine haematology and blood qPCR screening may enhance early detection of EEHV infection in susceptible elephants.