Bioparameters consistency of elephant endotheliotropic herpesvirus infection in captive asian elephants (elephas maximus) in Thailand

Abstract

Elephant endotheliotropic herpesvirus hemorrhagic disease (EEHV-HD) is a highly virulent disease that causes severe hemorrhage and sudden death in young Asian elephant calves. So far, epidemiological data and risk factors in Thailand related to EEHV-HD development are scarce and require additional studies to obtain a better understanding and further information on this disease. In this study, we report the demography, disease characteristics and mortality rate of ss elephants with confirmed EEHV-HD between January 2006 and August 201s using retrospective data subjected to survival analysis. Median age of EEHV presentation was 2.5 years, and the mortality rate was 68.97 % with a median survival time of 36 hours. The hazard ratio analysis identified application of medical procedures and antiviral medications as significant factors correlated to the risk of death. Moreover, change in hematology profiles is one indicator of infection for carly diagnosis and disease monitoring in suspected calves before clinical signs appear; however, to be effective, individual baselines and age-matched reference values are needed. Stress has been speculated to be a factor in clinical EEHV cases, but relationships have not been demonstrated empirically. This study evaluated blood hematology and several stress response markers salivary cortisol, fecal glucocorticoid metabolites (FGM),salivary immunoglobulin A (SIgA) and fecal IgA (FlgA) in samples collected for a year from three healthy calves with no prior EEHV history (non-EEHV) and six that had previously been infected with EEHV, developed clinical signs, and survived (prior- EEHV). One of those calves became re-infected, developed HD, and died during the study period. Hematology values between non-EEHV and prior-EEHV elephants were not different and within published reference ranges. The one clinical EEHV-HD case exhibited lymphocytopenia, monocytopenia, and thrombocytopenia, as documented previously. Concentrations of salivary cortisol, FGM, SIgA, and FIgA were variable and showed seasonal differences, but no relationships to EEHV status. Thus, in this preliminary study, while hematology was informative, none of the stress-response measures were predictive of EEHV status. Lastly, results from this study indicate a need to focus on EEHV monitoring efforts of young elephants and to follow current protocols that advise starting treatments before clinical signs appear might be able to be reduced loss in the young elephant population.