Spotlight on Zoo Science
April 1, 2005
Tracking an Elephant Killer
National Zoo scientists are trying to solve the case of a virus that kills elephants.
In 1995, the National Zoo community was devastated by the sudden death of Kumari, the 16-month-old baby Asian elephant, from a previously unidentified disease. National Zoo pathologists Laura Richman and Richard Montali found evidence of a herpesvirus infection. After further investigation, they discovered it was a novel herpes virus that causes a hemorrhagic (bleeding) disease in elephants.
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| EEHV causes extensive bleeding in an elephant's heart. |
By going through old zoo records and testing archived tissue samples, they realized that the same mysterious illness had killed other zoo and circus elephants. Richman went on to do her Ph.D. research at Johns Hopkins University on the virus, now called Elephant Endotheliotropic Herpesvirus or EEHV. Elephant Endotheliotropic Herpesvirus infects only elephants; it does not originate from or infect humans.
There are two forms of EEHV. One form is latent (doesn't cause disease) in African elephants, but causes the fatal disease in Asian elephants; the other form causes the disease in African elephants. Asian elephants may be infected with EEHV when they come into contact with African elephants, although there have also been cases in Asian elephants that have not been exposed to African elephants.
There is some hope: treatment with famciclovir (an anti-herpes drug used to treat herpes simplex and shingles in humans) has saved four elephants with EEHV. Unfortunately, eight elephants that were treated with famciclovir still died. We don’t yet know why the treatment sometimes fails.
National Zoo On The Case
The National EEHV Laboratory at the National Zoo, managed by Erin Latimer, tests samples from all over North America for EEHV. Blood samples from elephants that are showing symptoms of possible EEHV—head and neck edema (swelling), tongue cyanosis (bruising), and lethargy—are sent to the National Zoo for diagnosis by polymerase chain reaction (PCR).
The PCR test is a sensitive test that can detect very small amounts of the viral DNA in an active case of EEHV. It can also be used to detect the virus in tissue samples from previous cases, to confirm the diagnosis. Because of the acute nature of the disease, elephants with these symptoms are immediately started on famciclovir, even before the diagnosis is confirmed, to increase their chance of survival. The PCR test has never been positive in a healthy elephant or an elephant that is ill with another disease.
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| This image shows herpesviruses emerging from an inclusion body within an endothelial cell in an elephant's heart. An inclusion body is a body within a cell that is typical of some diseases. Endothelial cells line blood vessels. |
In addition, the National EEHV Lab is testing serum from apparently healthy elephants from North America, to help determine the epidemiology of EEHV. Serum contains antibodies, which can show previous exposure to a given disease. The EEHV Lab uses a test called an enzyme-linked immunosorbent assay (ELISA) to look for antibodies to either the Asian or African form of the virus.
Results from about 1,000 serum samples will be studied, along with records of each elephant’s contacts with other elephants within a facility, and among different facilities as a result of their moving from place to place. This will help elucidate viral transmission patterns. If the virus is periodically shed by carrier animals, movement between facilities, sometimes done for breeding or other purposes, could potentially be controlled.
Remaining Mysteries
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| Zoo scientists are trying to discover why some elephants get EEHV and others don't. |
A big question that needs to be answered is why some elephants get the disease and others do not. Fourteen of 21 cases in North America have been in elephants younger than seven years of age. Yet seven of the cases were in adults. Why do some adults get it and not others? Where are the elephants getting it from? There have been cases of vertical transmission—mother to child—in Europe, where some still-born elephants were positive for EEHV.
Are some elephants carriers of EEHV and periodically shed the virus? Are most elephants resistant to the disease, and if so, why? Are elephants more likely to get the disease at certain times, for example, during periods of stress, when their immune systems are impaired, or at certain times of the year?
We can answer why is it important to study this disease. Elephants are endangered and breed poorly in captivity. When they do breed, infant mortality is high—30 percent. About half of the deaths of young elephants are due to EEHV. In addition, the elephants in captivity are reproductively impaired. Some of the females are not fertile; others are older and may not be fertile much longer. Elephants can no longer be imported from the wild, so in 20 to 30 years the captive breeding populations may be reproductively unfit unless something is done to increase the survival of young animals.
The National EEHV laboratory is pleased to have the support of numerous veterinarians, elephant and herpesvirus researchers, and conservation societies, along with the American Zoo and Aquarium Association (AZA) and its Elephant Species Survival Plan (SSP).
Together, we hope to curtail the toll EEHV has placed on our precious elephant population. The future has recently brightened with the fourth known survivor of EEHV, a juvenile Asian elephant that was treated with famciclovir.
The EEHV Laboratory is supported by The Sisley Foundation and Feld Entertainment/Ringling Bros. and Barnum & Bailey Circus and the Center for Elephant Conservation.
Note to Media: If you would like more information about this project, or any of the Zoo's conservation and science programs, please contact the Zoo's Office of Public Affairs.
