Infectious Diseases Management in Asian Elephant : TB and EEHV-HD

Abstract

Asian elephant’s health, well-being and population sustainability are affected by several life-threatening diseases. Tuberculosis (TB), with potential zoonotic impact, and EEHV-HD, live threatening especially for young elephants, are amongst the most serious ones. Besides, they have the potential to severely affect the economy, particularly in relation to tourism. Infections of elephants with M. tuberculosis and EEHV have been reported worldwide, in Thailand frequent contact between elephants and M. tuberculosis infected human individuals, as well as between wild and captive elephants is likely. Our study, three reacted positive in a serological test (TB STAT Pak, Chembio). In serum of one of these, antibodies were found retrospectively, 23 months prior to bacterial culture from trunk wash samples. Sequence analysis of M. tuberculosis isolates from the four animals classified them as ancient strains (n=1) based on presence of a M. tuberculosis specific deletion (TbD1) and modern strains (n=3) identical to M. tuberculosis ATCC 2794. Detection of interferon gamma (IFN-γ) in a range of cytokines produced upon stimulation with M. tuberculosis derived antigens, is used for diagnosis at the early stage of infection with M. tb. Detection levels ranging between 1 and 10,000 pg/ml and able to detect native elephant IFN-γ of both African and Asian elephant whole blood cultures. Among Asian elephants, of different TB status, detection of IFN-γ upon in vitro stimulation of whole blood samples with ESAT6/CFP10, PPDB and PPDA, was negative for samples from non-infected elephants, as well as those from an elephant suspected of TB. Whole blood cell stimulation of a M. tb infected elephant with antigens ESAT6/CFP10 PPDB and PPDA resulted in detection of interferon gamma in all cultures, though to a lesser extent when stimulated with PPDA as a control for non MTBC environmental mycobacteria contact. ELISA results of serum samples of 708 elephants were subjected to Latent Class Analysis (LCA) to predict their serological TB statuses. Depending on LCA approaches, in case population versus individual elephant based, relative numbers (percentages) for the different statuses were “positive” 15-17.3%, “inconclusive” 48.7-50% and “negative” 34-35% of the animals. In this study, the North region had the lowest percentages of elephants predicted to be of positive serological TB status. The West region and to a lesser extend the other regions showed clearly higher percentages. Haemorrhagic Disease caused by Elephant Endotheliotropic Herpes Virus (EEHV-HD) we performed a cross sectional serological survey, using an EEHV1 glycoprotein B (gB) specific antibody ELISA. Of 994 elephants included in the study 42.3% were positive and 57.7%negative, while none were inconclusive, based on the criterion that a serum sample is considered positive if at least one serum dilution tested positive. Associations between seropositivity and potential risk factors for EEHV infection in the final multivariable regression model the variable “region” was represented. Finally, publication of this thesis will increase professional and public awareness of the threats of TB and EEHV infection in Elephants in Thailand