Elephant Endotheliotropic Herpesvirus (EEHV) and Hemorrhagic Disease (HD)

Today, all three extant elephant species – Asian (Elephas maximus), African savannah (Loxodonta africana), and African forest elephants (Loxodonta cyclotis) – are in danger of extinction from many fronts. Infectious diseases are yet another emerging threat to species survival, including elephant endotheliotropic herpesvirus (EEHV) hemorrhagic disease (HD).

 

Elephant endotheliotropic herpesviruses (EEHVs) have co-evolved with their hosts over millions of years. Both Asian and African elephants have their own distinct types, which normally cause natural lifelong infections with few health effects. However, in young elephants lacking sufficient immunity, the virus can cause acute, massive internal hemorrhage. With a case-fatality rate of up to 85%, EEHV-HD is the largest cause of mortality in young Asian elephants in western zoos, and it is now also recognized as an emerging threat in African elephants. Increasing reports have been documented in Asian elephant range states, with numerous cases recorded in Thailand, India, and Myanmar, including in a few wild elephants. EEHV-HD jeopardizes the sustainability of elephants under human care and the viability of ex situ populations as a buffer against extinction.

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Our research projects apply an epidemiological approach to identifying risk factors for EEHV-HD in managed elephants around the world. By leveraging our access to ex situ populations, we can also better understand the potential risk to wild elephants.

 

How Herd Dynamics Affect EEHV Immune Status in North America 

To better understand the distribution of EEHV infections in the North American population, we are carrying out a serology study in United States holding institutions. Serology is a critical component of herd management, allowing clinicians to determine exposure history in adults and monitor calves during the critical age of susceptibility. This project aims to characterize the at-risk population and estimate the seroprevalence of different EEHV types in both Asian and African elephants. Additionally, how herd size, structure, dynamics, and management factors influence EEHV immune status is not fully understood at present. Our research seeks to explore these potential risk factors, hopefully leading to actionable management practices to mitigate the impact of EEHV-HD on managed elephant populations globally. 

 

Impact of EEHV in Myanmar

Myanmar is home to approximately 2000 free-ranging and 5000 semi-managed working elephants, which share habitat and interact with their wild counterparts without human interference. Shrinking forest cover leads to increasing fragmentation, smaller herds, and closer contact between managed and free-ranging populations. This suggests that EEHV transmission with wild populations may be occurring at this interface, but with unknown health implications.

 

With limited diagnostic capacity to definitively confirm suspected cases, very little is currently known about EEHV in Myanmar. Our project seeks to expand our understanding of EEHV-HD epidemiology and evaluate its impact in the region by generating baseline data on background disease rates and identifying risk factors. Our research aims to: estimate seroprevalence and other disease measures for EEHV in Myanmar’s managed elephants; characterize the timing of waning of maternal antibodies in calves; and detect EEHV shedding using non-invasive, opportunistic sampling from wild elephants.

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This study was made possible with support from Morris Animal Foundation, whose mission is to bridge science and resources to advance the health of animals. Morris Animal Foundation is a 501(c)3 nonprofit organization. The Foundation relies upon donations from animal lovers and veterinarians, as well as nonprofit and for-profit organizations, to accelerate urgently needed breakthroughs in veterinary medicine. Visit morrisanimalfoundation.org to learn more.

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