Elephant calf at Chester Zoo

EEHV: Frequently asked questions

Q1. What is elephant endotheliotropic herpesvirus (EEHV) and why can’t it be treated?

A1. Elephant endotheliotropic herpesvirus (EEHV) is a type of herpesvirus, which can cause a highly fatal haemorrhagic disease when transmitted to young Asian elephants. When there is enough virus present in the blood to create a positive diagnosis, or when symptoms start to show, it is normally too late to treat the disease. 

EEHV doesn’t discriminate. Whether it’s an 18-month-old calf at Chester Zoo, or the young of a herd in the wilds of Asia, EEHV can strike without warning. As well as the deaths we are aware of in zoos, EEHV is known to have caused deaths in at least seven countries across the Asian elephant range in the wild – India, Nepal, Thailand, Cambodia, Laos, Indonesia (Sumatra) and Myanmar.

There are various strains of EEHV, which have affected young elephants. Currently there is no vaccination against it as researchers have yet to be able to culture the virus which is necessary to create a vaccine and determine what drugs are most effective.

Chester Zoo is at the forefront of ongoing international collaborative research into EEHV in the hope of a breakthrough that will enable us to ultimately prevent this global disease.

We are part of the global conservation community committed to researching EEHV and finding ways of improving outcomes for elephants which develop the virus and ultimately develop a preventative vaccine.

Q2. Can you tell me more about the ground-breaking research Chester Zoo is conducting to try to find a cure for the virus?

A2. Chester Zoo scientists - backed by more than £220,000 of public donations, a major partnership with The University of Surrey, and an international collaboration of conservationists - are making progress in the ongoing fight to find a cure for EEHV, but the journey is a long one.

Since we launched this Never Forget campaign in 2016, the research funding has helped to provide:

  • A Chester Zoo Conservation Fellow, post-doctoral position to work in collaboration with the University of Surrey and the Animal and Plant Health Agency (APHA). Dr Tanja Maehr’s research involves identifying some of the key mechanisms and elements of the elephant’s immune system to find a way to control the effects of EEHV.
  • Chester Zoo’s Veterinary Manager and one of the zoo’s Conservation Scholars have published results of a scientific study assessing a blood sampling technique to help in the detection of EEHV, as part of efforts to disseminate information among scientists fighting the disease worldwide.
  • Zoo staff have been working closely with the leading Virologist at APHA, who developed a method to detect EEHV, to gain understanding of the equipment & materials needed to treat EEHV.
  • A PCR (polymerase chain reaction) machine which tests blood samples on site at the zoo to provide immediate test results, enabling the zoo’s teams of keepers and vets to monitor the elephants daily and act more quickly in the case of a positive test.

Q3. Can EEHV be treated with the application of antiviral drugs?

A3. Frequent blood testing means that we can begin anti-viral treatment before a calf shows any outward physical symptoms. As soon as we detect any change we begin treatment but sadly this is a disease that takes hold very quickly and treatment is rarely effective.

Q4. Is the disease only found in zoo animals and can it spread?

A4. This virus does not discriminate between zoo elephants and elephants in the wild. Whether it’s a calf at Chester Zoo, or the young of a herd in the wilds of Asia, EEHV can strike without any known causes or reason. Research is ongoing but there is still a way to go before we fully understand this disease and how it manifests itself in some elephants and not others.

Q5. Will other elephants at Chester Zoo be susceptible to the disease?

A5. The elephants most susceptible are those around the age of weaning. In many the virus can lie dormant and undetectable and never develops into the disease. We are yet to learn why some elephants get it and others don’t.

Q6. How are the other young elephants in the herd, Anjan and Indali? Are they at risk?

A6. Anjan and Indali are both doing really well and are currently showing no signs of illness. This is a difficult time for the close-knit family herd, but they will pull together and care for each other. They are all under the watchful eye of our dedicated team.

Q7. Would keeping young elephants in isolation help tackle the disease?

A7. The reality is that EEHV is a very common endemic virus in elephants which can lie dormant, so keeping an animal in isolation would not be the answer. We work hard to maintain a natural, happy and healthy structure for the herd (which comprises four generations) to ensure both the physical and social well-being of the elephants. Creating clinical conditions is not the answer.

Q8. What do you do to monitor the elephants?

A8. Our elephant, science and veterinary teams work closely with the elephants, monitoring their health on a daily basis. Our elephant house has a special training bay for our young elephants and we have specially trained our keepers so that we can very easily take blood samples and conduct mouth checks. We use the very latest PCR (polymerase chain reaction) technology to test for the herpes virus. It enables us to amplify a single copy or a few copies of a piece of DNA, generating thousands to millions of copies of a particular DNA sequence. This means that we can detect the slightest change and start drug treatment immediately.

Q9. What is being done to prevent further occurrences?

A9. We carry out frequent blood tests on our young elephants to give us the best possible chance of catching the virus and administering treatment early (more information in A5).

Meanwhile, we are undertaking extensive research into this in the hope that one day a cure can be found to help the endangered Asian elephant. Co-operative multi-institutional research efforts have been underway for many years to study EEHV, identify the various strains, learn about their transmission, develop and improve treatments and hopefully find a vaccine. We are part of the collaborative international effort which has already led to more effective testing and earlier detection.

Our research to date has advanced our knowledge of the genetics of the virus and of the specific nature of the elephant’s immune response, both important areas to understand in order to develop effective treatments and preventions.

We are researching the times at which adult elephants are likely to be shedding more of the virus with a view to trying to predict periods of high risk for susceptible calves within a family herd. Progress in these areas is directly informing and enabling effective preventative strategies. 

It is not a cure, but we have identified medication which may act as an immune system boost to help the calves through the critical period of weaning when they are most at risk of developing symptoms of the disease; this is being used within our own herd.

Work is progressing on a therapy using proteins called interferons, which are part of the natural immune response. Our researchers have also actively been pursuing prevention strategies that include the potential for developing a vaccine. 

We would like to understand further the distribution and prevalence of this devastating disease in the natural ranges countries of the Asian elephant; we know that it is steadily being detected in more and more wild populations. The more we know about exactly where it occurs and why, the closer we will be to finding a solution.

A lasting preventative solution to this disease does not yet exist, and it is a long process, but we are moving closer.

Q10. Is this a recurring event for Chester Zoo’s herd of Asian elephants?

A10. The disease can affect Asian elephants in all zoos and in the wild and is indiscriminate. Chester has a large breeding herd of elephants regularly producing calves, which means we regularly have calves at the susceptible weaning age. Research is ongoing and along with other zoos, we contribute funds to research projects and play an active role in international efforts to tackle this devastating disease. If we are going to find a cure to this devastating virus, it is most likely to result from zoo led research.

Q11. Is this down to poor hygiene or ineffective husbandry practices?

A11. No, our keepers work hand in hand with our animal management and veterinary teams to ensure we are delivering world-leading care to all our animals.

Q12. Does this virus affect African elephants too?

A12. It does, but it is much milder in African elephants and rarely proves fatal.

Q13. Will you stop breeding elephants at Chester Zoo?

A13. No. To lose any elephant is devastating but we have a responsibility to do everything we can to understand this disease in order to have a chance of eradicating it both in zoos and, crucially, in the wild. Asian elephants are already endangered and it is hoped that the work being done in zoos will hold the key to unlocking the information researchers need to make a positive breakthrough. At Chester Zoo we have been hugely successful in breeding Asian elephants and we are committed to continuing with these important conservation efforts.

Q14. How widespread is the disease?

A14. We know EEHV has been recorded in at least seven countries across the Asian elephant range in the wild – India, Nepal, Thailand, Cambodia, Laos, Indonesia (Sumatra) and Myanmar.

Q15. Have elephants in other zoos encountered EEHV?

A15. Yes, many other zoos across Europe, USA and Australasia have had elephants affected by the virus.

Q16. Can this condition affect other animals?

A16. EEHV only affects elephants.

Q17. What is the effect on the rest of the herd when an elephants dies?

A17. Elephants are highly social animals so any death will affect them, particularly losing a young offspring – just as it does in the wild. They go through a grieving process but do soon move on from it.