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Scientists comment on a herpesvirus outbreak at Dublin Zoo.
Prof Julian Chantrey, Professor of Veterinary Pathology, University of Liverpool, said:
“I don’t have any specific knowledge about the cases at Dublin Zoo, but the disease caused by Elephant Endotheliotropic Herpesvirus (EEHV) is widespread globally, being present in many Asian elephant populations in European and American zoos and also in the wild, such as in Thailand, NE India and Myanmar. So sadly, the disease caused by this virus is having a serious negative impact on both wild and captive elephant populations.
“This disease has been a major problem in captive elephant herds for the last 30 years, by causing death through internal bleeding. Numerous European zoos have lost elephants to it. Some of the most established zoos with EEHV experience have had some success in pulling animals though infection (which is sometimes possible with early detection) but sadly not always. Adult elephants can have a degree level of immunity to infection which is transferred to youngsters in milk, so weaning is an especially difficult time when they are often affected. Dublin Zoo seems to be experiencing what other zoos have in the last few years. With massive, potentially dangerous animals like elephants, it is difficult to get successful treatment outcomes, even more so when elephants are seriously sick and the herd is stressed.
“So, this is not a new disease and unfortunately cases like this are not unusual. The best long-term solution to beating EEHV is to find a safe and effective vaccine, which is most likely to be achieved through zoo-led research. Scientists and elephant experts have been involved in international efforts to tackle this disease crisis and to develop a vaccine, with pilot trials having taken place in the UK and US.”
Dr. Priya Bapodra-Villaverde, Senior Veterinarian, Colombus Zoo and Aquarium Fellow of the Royal College of Veterinary Surgeons, said:
“EEHV is a virus that has co-evolved with elephants for millions of years, and is found in both Asian and African elephants under human care and in their native ranges. When initially infected with the virus, some calves are able to systemically manage the virus, just as in some humans who are unaffected by herpesvirus infections, with minimal or no clinical signs. However, in some young elephants, they are unable to control the virus especially if they still don’t have protective antibodies from their dam, resulting in a dangerous and often fatal illness known as EEHV hemorrhagic disease. This virus is having a significant impact on elephant populations under human care, but major advances in understanding EEHV biology, EEHV Hemorrhagic disease diagnosis and treatment, and immunity to EEHV have been made in the last two decades. These advances were made possible by funding and samples provided by North American and European zoological institutions. Recent advances in the ability to measure antibody levels against EEHV are a new tool to better identify elephants with the lowest immunity, and highest risk of EEHV Hemorrhagic Disease, although these tools are not yet available worldwide. Vaccine development is also underway worldwide, to try and reduce the impact of EEHV in managed herds.”
Dr Rachael Tarlinton, Associate Professor in Veterinary Virology, University of Nottingham, said:
“EEHV is a really difficult disease to deal with in Asian Elephant populations. It’s a herpesvirus that we now know is really widespread in wild and captive populations and has been with them for a long time. Nearly all adult animals have been exposed to it in their lives and many of them clearly get over the infection and go on to live normal lifespans. However the virus remains with the animal for life and is excreted occasionally from mucosal surfaces (eyes, trunk, vagina), mostly without causing any apparent problems. Human herpesviruses like those that cause cold sores do the same thing.
We don’t really know why most animals get over it without problems but a some get really severe disease and die. What we think is happening is that most problems occur on an animals first infection (severe disease is mostly seen in young animals) and it may be a combination of their immune response (at a time when protection from their mothers immunity is waning) and the genetics of the animal that makes them more likely to develop really severe disease. Some outbreaks (like the one in Dublin) occur after the introduction of a new animal (which is done to maintain genetic diversity in breeding programmes) and might be due to a new strain of the virus coming into the herd (virus strains vary too) . Animals at Dublin zoo have participated in genetic research here at Nottingham in the past but they haven’t had fatal cases before.
Treating the disease is really difficult, elephants are very large and are not the easiest animals to nurse. Treatment protocols usually rely on a combination of antivirals, IV fluids and nursing care but most animals that develop clinical disease still die. It is distressingly common with about ¼ of all the calves born in Europe and North America dying from EEHV. Breeding and disease is not as well documented in wild populations but we definitely see deaths there too and it’s a major problem for Asian elephant breeding and conservation programmes.
There has been some work put into developing diagnostics and preliminary work on a vaccine candidate but we are nowhere near being able to say we have treatments or vaccines that work reliably or that we know how best to control and prevent the disease ”
Declared interests
Dr Tarlinton: prior funding to work on EEHV from the BBSRC and has worked with many European zoos (Dublin included) who have provided samples for research
Prof Chantrey: none