Abstract
Thirteen new lethal cases of acute hemorrhagic disease (HD) with typical histopathogical features were identified in young Asian elephants (Elephas maximus indicus) in India between 2013 and 2017. Eight occurred amongst free-ranging wild herds, with three more in camp-raised orphans and two in captive-born calves. All were confirmed to have high levels of Elephant Endotheliotropic Herpesvirus type 1A (EEHV1A) DNA detected within gross pathological lesions from necropsy tissue by multi-locus PCR DNA sequencing. The strains involved were all significantly different from one another and from nine previously described cases from Southern India (which included one example of EEHV1B). Overall, eight selected dispersed PCR loci totaling up to 6.1-kb in size were analyzed for most of the 22 cases, with extensive subtype clustering data being obtained at four hypervariable gene loci. In addition to the previously identified U48(gH-TK) and U51(vGPCR1) gene loci, these included two newly identified E5(vGPCR5) and E54(vOX2-1) loci mapping far outside of the classic EEHV1A versus EEHV1B subtype chimeric domains and towards the novel end segments of the genome that had not been evaluated previously. The high levels of genetic divergence and mosaic scrambling observed between adjacent loci match closely to the overall range of divergence found within 45 analyzed North American and European cases, but include some common relatively unique polymorphic features and preferred subtypes that appear to distinguish most but not all Indian strains from both those in Thailand and those outside range countries. Furthermore, more than half of the Indian cases studied here involved calves living within wild herds, whereas nearly all other cases identified in Asia so far represent rescued camp orphans or captive-born calves.
Highlights
The deaths of more than 100 young endangered Asian elephant calves worldwide with acute hemorrhagic disease (HD) have been documented to be associated with a novel type of herpesvirus called Elephant Endotheliotropic herpesvirus (EEHV) found at very high levels in blood or necropsy tissue samples
Over the past 20 years, acute hemorrhagic disease occurring in young Asian elephants (Elephas maximus) born in captivity has been observed to have a fatality rate of about 80%
As reviewed by Long et al [5], EEHV HD has affected more than 20% of all Asian elephant calves born in North American and European zoos between 1995 and 2015, and has been the cause of 65% of the deaths that occurred amongst North American zoo or circus reared calves during that time period
Summary
The deaths of more than 100 young endangered Asian elephant calves worldwide with acute hemorrhagic disease (HD) have been documented to be associated with a novel type of herpesvirus called Elephant Endotheliotropic herpesvirus (EEHV) found at very high levels in blood or necropsy tissue samples. As reviewed by Long et al [5], EEHV HD has affected more than 20% of all Asian elephant calves born in North American and European zoos between 1995 and 2015, and has been the cause of 65% of the deaths that occurred amongst North American zoo or circus reared calves during that time period. Both lethal and symptomatic surviving cases proved to have massive systemic viremia with one of up to seven known species of EEHV. A similar lethal disease had been rumored to occur in Asian range countries in the mid-1990s, this was only confirmed to be EEHV HD much more recently by conventional PCR DNA sequencing of multiple cases mostly in India and Thailand
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