A virus is killing elephants, scientists are testing vaccines to help

February 17th 2022

Across the globe, an elephant specific virus called “elephant endotheliotropic herpesvirus,” or EEHV, a herpesvirus that has killed more than 70 elephants in zoos across Europe and North America and groups of wild elephants. The virus was first documented in 1995 by a group of scientists and veterinarians at the Smithsonian’s National Zoo in Washington D.C. When elephants contract the virus it either quickly manifests and leads to death within 5 days, or stays latent in their bodies long-term (similar to human herpesvirus). In fatal cases, the virus attacks endothelial cells (membranes that line the heart and blood vessels), rupturing blood vessels and causing significant blood loss throughout the body and heart. Elephants that survive the virus live with it for the rest of their lives with intermittent appearances of pink or white nodules on the head, trunk, or lungs while the virus lies dormant. Scientists believe that the virus is spread through trunk secretions, similar to human saliva. 

Since 1995 we have known about EEHV, but have had no cure. Indeed, even humans do not have a cure or vaccine for herpes. Some have successfully treated young calves with famciclover (a herpes antiviral produced via mouse testing to treat human herpes), but it can only treat one strain of EEHV and there are over 6 different strains. Otherwise, we must rely on the elephants’ natural immune system. 

But now there is hope for a vaccine. This week at Chester Zoo in Cheshire England, scientists and veterinarians are working together to test a vaccine long in the making. In fact, they are testing two different vaccines.

One is an MVA vaccine, or Modified Vaccinia Virus Ankara, which was developed over 50 years ago to treat smallpox. MVA is a mutant form of Vaccinia Virus Ankara which was a skin lesion causing virus from calves and donkeys. Scientists were able to get a mutant form of VVA by allowing it to grow and propagate in chicken cells in a dish to the point that it could no longer infect mammalian cells, which was confirmed via studies in rabbits and monkeys. MVA was then developed for humans to treat smallpox in a first trial of 100 patients, and second trial of 700 patients, and a third in 120,000 without severe adverse effects. 

Now scientists have modified MVA again by placing the DNA of EEHV into the virus. This should trick the immune system to make antibodies for EEHV and then launch an attack when the body of the elephant inevitably comes into contact with EEHV.

The other vaccine is a protein based vaccine. A protein vaccine is made by producing the proteins the elephants’ bodies make when exposed to EEHV. This allows us to expose the elephant to unharmful proteins that look like the proteins from the virus, thereby allowing the immune system to make antibodies that would be able to successfully attack the EEHV virus and protect the elephants from dying. Similar vaccines have been developed for COVID.

While these vaccines are being tested and appear promising, they must undergo safety and efficacy in elephants because there are no alternative models. So it will be a while before we know whether either vaccine is good for combating EEHV and even longer until we can use it across the globe. 

– Justin Varholick, Ph.D.

Sources and further reading:

EEHV Advisory Group https://eehvinfo.org/
History of MVA vaccines https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7112317/
Chester Zoo news: https://www.chesterzoo.org/news/the-research-race-for-an-eehv-vaccine/
https://www.chesterzoo.org/news/worlds-first-pilot-study-to-fight-deadly-elephant-virus

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