MEASURES OF DISEASE FREQUENCY FOR ELEPHANT ENDOTHELIOTROPIC HERPESVIRUS INFECTION AND HEMORRHAGIC DISEASE IN THE UNITED STATES ELEPHANT POPULATION FROM 2014 TO 2024.

Elephant endotheliotropic herpesvirus hemorrhagic disease (EEHV-HD) is an important cause of morbidity and mortality in juvenile Asian (Elephas maximus) and African (Loxodonta africana) elephants in human care. Measures of disease frequency have not been rigorously established for EEHV in any elephant population. The objective of this retrospective descriptive epidemiologic study was to determine period prevalence, cumulative incidence, and incidence rate (IR) for EEHV infection and EEHV-HD in the US elephant population between 2014 and 2024. A case of EEHV infection was defined as an elephant of any age with an episode of EEHV viremia with levels >1,000 viral genome equivalents (vge)/ml, and a case of EEHV-HD was defined as a juvenile elephant with EEHV viremia levels >5,000 vge/ml, along with the presence of clinical signs, blood work abnormalities, or pathologic evidence suggesting vasculopathy. After institutional approval for data transfer, deidentified whole-blood EEHV qPCR results from the National Zoo Elephant Herpesvirus Laboratory were analyzed. The data originated from 30 zoos, encompassing 234 elephants, and included >23,000 PCR reactions. EEHV1A and 3A were the most prevalent and incident EEHV types for Asian and African elephants, respectively. Analyses indicated that if 100 juvenile Asian elephants were monitored over 1 yr, 7.91 new cases of EEHV1A-HD would occur in the United States. Similarly, 4.81 new cases of EEHV3A-HD would be expected to occur if 100 juvenile African elephants were monitored over 1 yr in the United States. EEHV6-HD appears to pose an underreported threat to African elephants with an IR of 1.46/100 elephant years.