Elephant Endotheliotropic Herpesvirus Infection in Captive Asian Elephants (Elephas maximus) in Thailand: Implications for Conservation and Health Management

Elephant Endotheliotropic Herpesvirus (EEHV) infection is of conservation concern to endangered Asian elephants (Elephas maximus), causing severe, acute, often fatal haemorrhagic disease in young elephants. This thesis investigates the epidemiological status of clinical and subclinical EEHV infection in Thailand, through a retrospective, a cross-sectional, and a longitudinal study in captive elephants. Novel diagnostic tools were developed and recommendations discussed, with a particular focus on practical recommendations to manage EEHV infection in Thailand, where logistical and management constraints can hamper disease diagnosis and timely treatment. The retrospective study revealed at least 18 EEHV clinical cases in Thailand (2006–2014), with only two cases surviving following intensive treatment. Viral samples from each case were not identical based on multiple gene analysis; suggesting the disease is likely to be sporadic. The findings also suggest that EEHV1A and EEHV1B are likely endogenous pathogens in Asian elephants. A novel SYBR green I-based real-time PCR assay was developed to identify subclinical infection, diagnose early infection, and monitor disease progression. This technique provided sufficient data, with appropriate detection limits to differentiate at least three types of EEHV (EEHV1A, 1B, and 4). Applying this technology to the cross-sectional study, conducted between 2013–2015, revealed a 5.5% prevalence of asymptomatic EEHV1 infection during this study period in captive Asian elephants in Thailand. Cross-sectional analysis did not find an association between EEHV infection and sex, location, or contact history with other EEHV-positive elephants; however, EEHV was more likely to be detected in juveniles than other age classes (OR = 4.46; 95%CI: 1.60–12.45; p = 0.05). The study also monitored EEHV shedding patterns longitudinally in an EEHV-positive herd. Frequency of EEHV detection varied within and between individuals, but was significantly higher in elephants which had survived previous clinical EEHV infection (OR = 4.85; 95%CI: 0.88–26.74; p = 0.05). Concurrent monitoring of faecal corticosterone metabolites demonstrated that EEHV activated and reactivated spontaneously and shed sporadically, despite lack of obvious stress. This thesis describes the first intensive EEHV study in an Asian elephant range country. The thesis assesses the novel real-time PCR protocol and current diagnostic tools, and recommends practical management and disease preparedness strategies to minimise the impacts of EEHV on wild and captive populations, both locally and internationally