Elephant calf at Chester Zoo

EEHV: Frequently asked questions

Q1. What is elephant endotheliotropic herpesvirus (EEHV) and why can’t it be treated?
A1. There are various strains of the EEHV, which has affected young elephants typically around weaning age. EEHV strikes elephants both in the wild and in zoos. 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. At present, drug treatment is effective in only around 20% - 30% of cases. International collaborative research into EEHV is ongoing in the hope of a breakthrough that will enable us to ultimately prevent the disease.

Here at Chester Zoo 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 EEHV be treated with the application of antiviral drugs?
A2. Our weekly 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 effective in only around a quarter of cases. 

Q3. Is the disease only found in zoo animals and can it spread?
A3. This virus does not discriminate between zoo elephants and elephants in the wild. 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. 

Q4. Will Nandita - or any other elephants at Chester Zoo - be susceptible to the disease?
A4. The virus affects elephants broadly between the ages of two and eight so the adult members of our herd are not at risk. 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.

Q5. What do you do to monitor the elephants?
A5. Our elephant, science and veterinary teams work closely with the elephants, monitoring their health on a daily basis. Over the last two years we have modified the elephant house with a 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. 

Q6. Is it a genetic condition?
A6. Like any other disease there may be a genetic predisposition in some animals, but we can say with confidence that it is not a genetic condition.

Q7. What is being done to prevent further occurrences?
A7. We do blood tests on our young elephants weekly to give us the best possible chance of catching the virus and administering treatment early (more information in A5).
We will continue to support the research into this in the hope that one day a vaccine 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.

Q8. Is this a recurring event for Chester Zoo’s herd of Asian elephants?
A8. 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.

Q9. Would keeping young elephants in isolation help tackle the disease?
A9. 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 our herd (which comprises three generations) to ensure both the physical and social well-being of our elephants. Creating clinical conditions is not what we are about. 

Q10. Is this down to poor hygiene or ineffective husbandry practices?
A10. Absolutely not. 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.

Q11. Does this virus affect African elephants too?
A11. It does, but it is much milder in African elephants and rarely proves fatal.

Q12. Will you stop breeding elephants at Chester Zoo?
A12. No. To lose an 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.

Q13. How widespread is the disease?
A13. We know of 80 recorded deaths to date. As well as the deaths we are aware of in zoos, 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.

Q14. Can this condition affect other animals?
A14. EEHV only affects elephants.

Q15. What is the effect on the rest of the herd when an elephants dies?
A15. 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 very short grieving process but move on from it very quickly.

Q16. Have elephants in other zoos encountered EEHV?
A16. Yes, many other zoos in Europe and the USA have had elephants affected by the virus.