Pathogenic characteristics of elephant endotheliotropic herpesvirus infection in Asian elephants.

Elephant endotheliotropic herpesviruses (EEHVs) are responsible for a highly fatal haemorrhagic disease (EEHV-HD), threatening the overall sustainability of the Asian elephant (Elephas maximus) population. The viruses were first reported in tissue sections of a fatal case of an Asian elephant in 1988. In recent years, there has been a gradual increase in our understanding of the viruses highlighted by decoding their complete genome sequences. However, lack of an animal model and a cell culture system has restricted studies on the pathogenesis of the viruses, assessing control measures, and development of a vaccine. This project therefore aimed to achieve a better understanding of the viruses’ pathogenesis studying several EEHV surviving and fatal cases, and to advise accordingly on the control measures. The results revealed coincidence of highest blood viral load with clinical signs, viruses’ shedding in trunk secretion during convalescence, complementary haematological tests to aid detection and clinical prognosis of EEHV infections and the inadequacy of famciclovir treatment to alter EEHV infections. Analysis of tissues from fatal cases detected viruses’ co-infections (EEHV-1 and 4) and widespread organ distribution with liver, heart, mesenteric lymph node, thymus, and tongue having the highest viral load, thereby highlighting implications for EEHV diagnosis and future in vitro isolation. Further, this study isolated elephant endothelial cells and PBMCs and used these established elephant cells alongside common laboratory cell lines to assess their suitability for EEHV-1A isolation. Despite indication of limited increase in EEHV-1 DNA in PBMCs and mouse embryo fibroblast supernatants, conclusive in vitro virus replication could not be demonstrated. In conclusion, the outcomes of this PhD study further advance our knowledge on pathogenesis of EEHV strains and provide new insights on their control to minimise their respective impact on the Asian elephant population