CHANGES IN SERUM CARDIAC TROPONIN I IN ASIAN ELEPHANTS (ELEPHAS MAXIMUS) WITH ELEPHANT ENDOTHELIOTROPIC HERPESVIRUS INFECTION

Elephant endotheliotropic herpesvirus (EEHV) is one of the most important causes of mortality in Asian elephants (Elephas maximus). The unusual tropism of EEHV for endothelial cells of capillaries can lead to catastrophic vascular dysfunction, hemorrhage, cardiac damage, and death. Cardiac troponin I (cTnI) is an intracellular protein of cardiomyocytes that is released into circulation in levels directly correlated to the severity of cardiomyocyte damage. The purpose of this study was to assess if cTnI could be used to distinguish when EEHV viremia leads to clinical disease versus subclinical infection. Thirty-seven individual Asian elephants contributed 53 blood samples that were evaluated for EEHV viremia using quantitative polymerase chain reaction and analyzed for cTnI using a high-sensitivity assay. Viremia was categorized as none (24/53), low (< 20,000 vge/ml, 12/53) and high (>= 20,000 vge/ml, 17/53). Seven of the nonviremic samples had detectable cTnI. Nine low-viremia samples were positive for EEHV1 (1A and 1B combined) and lacked a detectable cTnI. Fourteen high-viremia samples were positive for EEHV1 and had detectable cTnI. There was statistical significance between having viremia and having a detectable cTnI value (P = 0.0001), and animals with EEHV1 viremia were more likely to have a positive cTnI value (P = 0.04). The presence of cTnI was associated with the presence of clinical signs, with higher values of cTnI in the presence of clinical signs versus subclinical viremia (P = 0.0001). In addition, four elephants contributed multiple samples from a single viremic event and results displayed a trend of elevation in troponin values with progression of EEHV viremia. The association of EEHV viremia with cTnI suggests these markers might be used in conjunction to help predict when EEHV viremia is likely to progress to EEHV-HD for an individual.