EEHV: Herpes infection often fatal to baby elephants

Posted on June 11, 2015   by Benjamin Thompson

It has been estimated that a staggering 90 per cent of the humans on Earth are infected with one or more viruses from the family Herpesviridae, which are commonly known as herpes viruses.

Members include Varicella Zoster virus, the causative agent of Chicken Pox, Herpes Simplex virus, which causes genital herpes and Cytomegalovirus – a virus that can be a serious problem for the immunocompromised.

While only eight types of herpes virus are able to infect humans, there are dozens more in the family, infecting organisms as diverse as oysters, cats and turtles. The vast majority of herpes viruses are host-specific and are only able to cause disease in the organism they have evolved to infect.

Tucked away in a phylogenetic subfamily of the Herpesviridae lives the relatively recently added genus Proboscivirus. This genus consists of seven viruses: EEHV-1 through to EEHV-7. EEHV is short for Elephant Endotheliotropic Herpesvirus, which, as its name suggests, causes disease in elephants. EEHV-1 appears to be the most pathogenic of the seven viruses and was first isolated from the lungs of an African elephant in 1971.

An EEHV infection in African elephants is relatively benign, causing lesions on the skin and other parts of the body. In Asian elephants, the effects are more severe: visible symptoms can include edema of the head and trunk, with internal haemorrhaging of major internal organs the likely cause of death from the disease.

EEHV disproportionally affects both wild and captive juvenile Asian elephants under 5 years old, with mortality rates estimated to be as high as 85 per cent. EEHV can kill an elephant within a week of the first appearance of symptoms. Human antivirals have been used to treat an infection, but their effectiveness is unknown.

It can come as no surprise that EEHV is a serious problem for the health of wild and captive elephants. Researchers are trying to learn more about this virus, in the hope that it can be effectively prevented or treated. Among them is Laura Bennett, a Society member and PhD student from the University of Nottingham, who is investigating how stress affects levels of virus in the elephants.

Stress seems to have an important role to play in the herpes infections. Herpes viruses are lifelong infections that often lie dormant for extended periods of time; in humans, stress is often associated with a ‘flare up’ of an infection. For example, research has shown that the rather stressful vocation of spaceflight can increase the levels of Varicella Zoster virus in an astronaut’s bloodstream.

Laura has been looking at whether subclinical levels of EEHV – those too low to cause disease – are increased during elephant pregnancy. To assess this, she has been working with colleagues at nearby Twycross Zoo, which has a herd of Asian elephants; two of these elephants were pregnant in the past three years. The keepers at the zoo trained the elephants to provide ‘trunk wash’ samples, which sees them sucking up some sterile saline, elevating their trunks for 30 seconds, then blowing the liquid out into a sealable bag.

These washes contain cells that line the inside of the elephants’ trunks, known as epithelial cells. Laura uses a technique known Quantitative PCR that can identify both the presence and levels of EEHV in the trunk wash samples.

Early results suggest the pregnancy does not affect levels of EEHV, so the group from the University of Nottingham is expanding their search to investigate the role that genetics may play and possible co-infections.

There are still many unknowns about EEHV: why some elephants get it, while others in the same herd do not; or whether it is passed from mother to offspring. Given the amount of pressures that Asian elephants face – poaching and habitat destruction, for example – removing another hurdle on the road to population growth would be a welcome development.

Image: Fabien Bastide on Wikipedia under CC BY-SA 3.0