Dead elephants at the Zurich zoo due to herpes – the virus is also dormant in humans

The mysterious elephant herpesvirus is only one of approximately 200 herpesviruses. Nine of them are in people – in each of us.

Bruno Knellwolf / ch media

Indi’s mother says goodbye to her daughter Omyha.nicole schnyder / zurich zoo

Cold sores, these are the little, annoying herpes. But the herpes virus family is much larger, and it even kills elephants. At the Zurich zoo, a two-year-old young bull, Umesh and an elephant cow, Omysha, died early in the week of infection with the “elephant herpes virus endothelial haemorrhagic disease” (EEHV-HD). Omysha did not respond to treatment with antiviral drugs or blood transfusions. The EEHV-HD virus can cause internal bleeding and organ failure.

From elephant to elephant

How the virus is transmitted is not yet entirely clear. “But the virus probably jumps from elephant to elephant,” says Pascal Marty, curator of the Zurich zoo. It is also unclear how the herpes virus is circulating in the wild. Wild animal research is not very advanced, says Marty.

This is confirmed by virologist Cornel Fraefel, director of the Institute of Virology at the University of Zurich:

«For EEHV-D the transmission path is unknown. However, it is likely that the virus will be transmitted from older animals to young elephants very early on. ‘

All elephants are assumed to be carriers of the virus, not only in the Zurich Zoo, but also in other zoos and in the wild. It turns out that the disease mainly breaks out in young elephants. The younger elephants may have made even fewer antibodies to EEHV-D, says Marty. “They have to increase it by repeated exposure to the virus.” Older animals are more likely to prevent outbreaks of disease with antibodies.

Corona viruses have jumped from animals to humans. This is not to be expected with the elephant herpes virus. “Herpes viruses are very host specific,” says virologist Fraefel. Once settled on the host, they remain loyal to him. “This host specificity depends on the cellular receptor that the virus uses to enter the cell.” In addition to the cell entry receptor, there are also intracellular factors, i.e. certain enzymes and other proteins, that play a role in determining the carrier of the herpes virus.

About 200 family members, nine of them are human

Of the large herpes virus family of about 200 known members, nine have chosen to host humans. The most famous disease is the herpes simplex mentioned initially, which causes “herpes simplex type 1 virus”. In addition, there are much more dangerous herpes viruses, such as the varicella zoster virus (VZV), which causes shingles, or the Epstein-Barr virus, which can cause glandular fever when infected. In addition, diseases caused by herpes viruses also include genital herpes, chicken pox, and various types of cancer.

Typical shingles pattern: the blisters touch the strip from the center of the body.

Typical shingles pattern: the blisters touch the strip from the center of the body.Image: Shutterstock

“In the case of human herpes viruses, transmission occurs through close contact, droplet infections, smear infections, childbirth, kissing, sex and the like,” explains the director of the Virology Institute. At the site of transmission, infectious cells that have the correct receptor or receptors for entry into the cell are required. According to virologist Cornel Fraefel, most herpes viruses use a receptor and a coreceptor.

Everyone carries the herpes virus

Herpes viruses have been accompanying people for millions of years and have adapted to our body accordingly. Once inside, they don’t want to leave for the rest of their lives. Every adult is a carrier of one or more of the nine human herpes viruses. It doesn’t have to be a disease. The initial infection often goes undetected, i.e. asymptomatic.

Herpes viruses remain latent. “For many viruses, latency is a strategy of staying in the host for extended periods of time without being detected and eliminated by the immune system,” says Cornel Fraefel. Viruses thus increase the chance of finding a new host – the same species, i.e. from human to human or from elephant to elephant. Depending on the herpes virus, few or no viral proteins are produced during the latency period. For example, none for herpes viruses and varicella zoster viruses, only a few for the Epstein-Barr virus. “This is how the viruses hide from the immune system,” says the virologist.

Various waiting rooms in the body

The location of the latency differs from herpesvirus to herpesvirus: for example, herpes viruses are located in the ganglia of sensory neurons during latency. Ganglia are collections of nerve cell bodies.

If there are blisters on the lips, this is called herpes labialis.

If there are blisters on the lips, this is called herpes labialis.Image: KEYSTONE

The Epstein-Barr virus is found in B lymphocytes. In varicella zoster viruses, latency occurs in the nerve roots of the spinal cord, dorsal root ganglia, and in the ganglia of the cranial nerves. The reactivation of this virus in these tissues then leads to herpes zoster. “Viruses not only disguise themselves by expressing a few viral genes or not, but also reside in tissues that are” immunocompromised “? they are, says Fraefel. That is, in tissues that cannot be destroyed by an immune response.

There is only a vaccine against the human herpes virus

It is this latency that is a problem in the development of vaccines against herpes viruses, explains Fraefel. Vaccination is prophylactic. However, since infection with many herpes viruses occurs during childhood and the viruses remain throughout life, vaccination is made difficult. Only against the herpes zoster virus is vaccination today. “Nevertheless, it is conceivable that in addition to the VZV vaccine, other vaccines will be developed against other herpes viruses in the future,” says Fraefel.

Vaccines already exist against several different herpes viruses for livestock and pets. For example against bovine herpes viruses, pseudorabies virus and equine herpes virus 1. “They do not prevent infection or latency, but reduce symptoms,” says Cornel Fraefel, director of the Institute of Virology at the University of Zurich. There are also effective antivirals for certain herpes viruses.

The zoo superintendent hopes to get vaccinated

There are still no vaccinations against the elephant herpes virus EEHV-D. “But research is ongoing and we hope the vaccine will hit the market soon,” says Pascal Marty of Zurich Zoo. The body of the elephant Omysh cow is currently being examined by pathologists at the Zurich Animal Hospital to gain insight into the mysterious herpes virus. (bzbasel.ch)

This elephant is taking apart an all-terrain vehicle – that’s it

Video: Watson

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