EAZA Elephant TAG EEHV Fund

Background

Elephant endotheliotropic herpesvirus (EEHV) continues to be a devastating infectious disease posing a significant threat to the long-term conservation of Asian elephants in zoo populations and is the most frequent cause of death in young Asian elephants in Western zoos. The disease is also found in wild populations, where infections and fatalities are more challenging to track. More recently, African elephants have been shown to be affected as well.

The co-existence of elephants with EEHV over the past four million years indicates that in young elephants’ lives there must be a protective element to prevent EEHV induced fatality. In captivity in North America and Europe, breeding institutions can be affected with EEHV infections with up to 100% mortality, whilst similar institutions (group size, breeding success) are unaffected or minimally affected.

This project investigates important elements in individuals’ lives (up to the age of 3 years) which allows them to resist EEHV as well as looking at factors which make them sensitive to EEHV (retrospective analysis of recent deaths). It is felt that nutritional components such as lauric acid play a key role in disease prevention. During active lactation, losses of calves are minimal indicating that elephant milk contains a protective component. Hand-reared calves are at high risk for EEHV infection. The weaning period (approx. 2 years) is a critical phase for young calves regarding EEHV infection.

Lauric acid is an antiviral and antibacterial fatty acid with a commercial use in antibiotic-free treatment against infection, widely used by human HIV patients. Lauric acid makes up 30-40% of free fatty acids in the milk of African elephants; data regarding Asian milk composition is unknown. Other nutritional components may protect weaning calves which may be absent from diseased weaning calves hence causing fatal EEHV infection.

Achievements and Objectives

Elephant endotheliotropic herpesvirus (EEHV), of which there are seven species and several subspecies, continues to be a devastating infectious disease posing a significant threat to the long-term conservation of Asian elephants in zoo populations. One in every six young Asian elephants born in western zoos develops an acute, haemorrhagic disease (EEHV-HD) as a result of an EEHV infection. Affected animals almost always succumb to disease, often within one to two days after the first clinical symptoms appear. EEHV-HD is the most common cause of death of young Asian elephants in zoos; 56% of all mortality among elephant calves is caused by this disease.

The disease is also found in free-ranging Asian elephant populations where infections and fatalities are more challenging to track; over 120 deaths have been attributed to EEHV-HD since 2003. In recent years, multiple young African elephants in zoos succumbed to EEHV-HD as well.

Over the past few years, researchers have worked to understand why some elephants get severely ill from this virus while others do not. They found that the antibodies a young elephant gets from its mother at birth protect it from the virus causing disease. However, these antibodies slowly disappear over two to three years. If an elephant has not encountered the virus by then, it is at high risk of dying from an infection.

In 2025, Colchester Zoological Society provided a donation of £854.04 to support research projects that strive towards finding a solution against this fatal disease.

Until just a few years ago, little was known about the EEHVs and the disease they may cause (EEHV-HD). For that reason, a research project with the eventual aim to develop a vaccine for and treatment against EEHV-HD was started at Utrecht University. Initially, the team developed new, reliable diagnostic assays with which antibodies against the EEHVs can be detected.

In addition to development of the assays, they have assessed what virus component would be the most suitable antigen for an EEHV vaccine. They have now developed a candidate vaccine against EEHV1A; subspecies 1A has been responsible for the vast majority of EEHV-HD cases to date and they have trialled the vaccine on zoo elephants with limited side effects. The aim now is to vaccinate young elephants that do not have any antibodies against the virus and are therefore at risk of getting seriously ill. It is important that vaccinated animals produce sufficient amounts of antibodies against the virus so the elephants will need to be monitored long-term to see if these antibodies (and thus vaccination) protect them against disease when they first come into contact with the virus.

Since antibodies are very important for the protection against EEHV-HD, they are also looking into the possibility to use EEHV-specific antibodies as a (prophylactic) treatment against EEHV-HD. Serum or plasma of adult elephants with high levels of EEHV-specific antibodies could be administrated to elephants at risk of EEHV-HD in order to increase their EEHV-specific antibody levels, so-called passive transfer of antibodies.

The future of zoo elephant populations depends on understanding how to manage this awful disease. In the long term, research serves to protect captive elephants against fatal EEHV-HD and contribute to the preservation of this endangered animal species.

Click for 2024 Summary

• In 2024, Colchester Zoological Society provided a donation of £866.63 to support research projects that strive towards finding a solution against this fatal disease.
• Promising lines of research work continue, with researchers at the University of Utrecht making remarkable progress towards developing a vaccine against EEHV.
• A scientific paper was published in 2024 highlighting progress with the work to better define which animals are at risk of EEHV-fatal haemorrhagic disease (EEHV-HD), using blood tests from 164 Asian elephants in European zoos. The study strongly suggested which young elephants with low antibody levels were at risk of developing fatal EEHV-HD, confirmed by the fact all 23 studied fatalities had such low antibody levels (which represents a large subset of 56% of the total reported fatalities).
• Overall, the research found that specific testing can be used to identify animals at risk of EEHV-HD and further research will now look to determine the exact antibody level above which animals are protected against EEHV-HD.
• The future of zoo elephant populations depends on understanding how to manage this awful disease. In the long term, research serves to protect captive elephants against fatal EEHV-HD and contribute to the preservation of this endangered animal species.