What is elephant herpes?
Elephant endotheliotropic herpesvirus – EEHV
(elephant endotheliotropic virus – hereinafter referred to as “herpes”)
Elephant herpes is caused by a set of herpes viruses that affect the elephant population of all species and all ages. The first death of an animal from these viruses was described in 1990, but the presence of herpes in the elephant population was already described in the 1970s. Backtesting of available samples found fatal cases in elephants in zoos as far back as 1983. Understanding of the disease has advanced significantly in recent years. The vast majority of fatal cases in the past occurred in Asian elephants; in African elephants in human care, it appears to a greater extent only in the last four years (2019 Indianapolis Zoo, USA – five cases, 2019 Fresno Chaffee Zoo – two cases, 2021 Vienna – two cases). The disease most often affected young animals in the age spectrum of 2–11 years. However, the Indianapolis cases show that herpes can fatally affect animals significantly older (35+). In these cases, the disease does not have such a dramatic course and can be confused with colic conditions. So it’s possible that in the past we’ve lost more older animals within communities that died of what appeared to be colic, but it was actually herpes, and animals that old weren’t tested postmortem for herpes.
Herpes is not just the domain of elephants in human care. It is also commonly found in the countries of origin, either in human care or in the wild. There are also active cases in the wild, and for fatal cases in recent years, cadavers are searched for in countries and subsequently tested positive.
Today we know that herpes is ubiquitous throughout the elephant population and appears in several strains. In Asian elephants, the strains are EEHV1a, EEHV1b, EEHV4 and EEHV5. In African elephants EEHV2, EEHV3 and EEHV6. Elephants regularly encounter the disease, and if they have experienced viremia, they need the antibodies they will need in the future. Herpes remains and from time to time at the same time reappears in the body, the elephant manages the disease thanks to antibodies, but I excrete it into my surroundings.
Baby elephants mainly acquire antibodies in placental form from their mother. The original assumption that agents are transferred during breastfeeding is questionable, the vast majority of fatal cases were fully breastfed. These representatives gradually decrease with the age of the elephant to zero (usually around 2.5-3 years of life). If the elephant encounters a disease by that time, thanks to the mother’s antibodies, you will be able to build up your own immunity. If he does not encounter a disease during the first three years of his life, he does not have the opportunity to build up and subsequent encounters with the disease will therefore lead to its full outbreak. However, due to the different strains, it is possible for the mother to pass on full resolution against EEHV1b and EEHV5. However, if it encounters the EEHV4 strain, it does not, and the disease breaks out fully again.
The problem with elephants in human care is that they shed significantly less herpes than in the wild. Elephants in zoos are closed communities, functioning practically for themselves. They meet other elephants in the wild, and the chance of meeting an elephant excreting herpes is high. In addition, the main reason for shedding herpes is stress. Life in nature is full of stress (struggle for resources, predators, humans and especially the social stress described above when meeting other groups of animals). Elephants in human care experience significantly less stress, practically none at all, and thus have no reason to excrete herpes. Therefore, our baby elephants do not have much of a chance to acquire antibodies, which is why the mortality rate of baby elephants in zoos is significantly higher. This is a completely new finding that was confirmed by research at the Oklahoma Zoo. This zoo tested elephants over the course of seven years at their request for herpes in the area. The colleagues described the different life situations of their herd and in the vast majority of cases the elephants excreted only trace amounts of the virus compared to the natural state. An increase in the excretion of the virus was evident, for example, during the treatment of herpes and the subsequent death of one member of the herd. No difference in shedding was seen when a new male arrived. Excretion of the herpes virus increased to many times greater values and was compared to the state in nature only with the arrival of two new elephants. Their arrival and subsequent association with the herd led to great social stress. We can therefore say that our elephants live in quality conditions without stress, which unfortunately also leads to an easier outbreak of disease and subsequent deaths. The breeding community is now unofficially dealing with a way to get “positive” stress into the group, which will lead to more frequent shedding of herpes and subsequent immunization of young animals. But all this must take place at a time when it is fully protected by antibodies from the mother. These are completely new findings from the fall of 2022, and it was already too late for us to try to introduce positive stress.
In the course of a viral infection, the number of platelets decreases until the stage when the hemorrhagic form breaks out. Symptoms of the disease are, in addition to the non-specific symptoms already mentioned, enlarged lymph nodes, swelling of the subcutaneous tissue of the head, neck, limbs and body, cyanosis/blueness of the tip of the tongue, blisters on the tongue, hemorrhages (punctate and branched) on internal organs and tissues, hemorrhages and swelling of the digestive system , ulcers in the mouth, esophagus and colon, enlarged liver, skin changes, subacute inflammation of the heart. All of this occurs as a result of damage to the epithelium of vessels and inflammatory changes that lead to blood clotting disorders (DIC – characterized by the formation of thrombin, a similar course is seen in e.g. Ebola or SARS) and the subsequent formation of hemorrhages and swelling in various parts of the body. is hypovolemic shock and/or organ failure, primarily the circulatory system.
A relatively effective method of treatment is therefore early recognition of the stage of the disease (by testing the blood, observing the changes in the elephant), administering a plasma transfusion, which should prevent the reduction of platelets, infusion therapy and the application of antivirals. An elephant has a significantly better chance of fighting the disease. The mortality rate in this phase is approximately 60%. After the onset of the clinical phase, the mortality rate is over 85%.
There is currently no EEHV vaccine available. A pilot vaccine project by the University of Surrey in the UK was launched at Chester Zoo and the vaccine was administered to an adult male elephant. The authors of the vaccine themselves claim that they are only in the early stages of vaccine development and it is difficult to predict whether the current form of the vaccine can stop in young animals.
Teams from the University of Utrecht (Netherlands) and Baylor College of Medicine (Texas, USA) are also working on the vaccine.
In mid-January 2023, the Prague Zoo contributed 1,000 euros for joint research on EEHV in European zoos that keep elephants.
Martin Kristen and Roman Vodička