National Elephant Herpesvirus Laboratory

The Smithsonian's National Zoo and Conservation Biology Institute is committed to preserving Asian and African elephants—both in human care and in the wild. As part of this mission, the Zoo researches diseases that afflict elephants, such as the elephant herpesvirus, known as elephant endotheliotropic herpesvirus (EEHV). Researchers at the Smithsonian’s National Zoo were the first to identify EEHV in 1995, following the death of our 16-month-old Asian elephant, Kumari, who was Shanthi’s first calf. Since then, these researchers have made significant discoveries on the biology of EEHV.

Elephants in human care and in the wild have been affected by EEHV, which has been responsible for about half of the deaths of young elephants in zoos. In response, cooperative multi-institutional research efforts have been underway for more than a decade to study EEHV, identify the various strains, learn about their transmission, develop and improve treatments, and find a vaccine. In the wild, elephants face extreme pressure from human-elephant conflict, habitat loss and poaching. In institutions accredited by the Association of Zoos and Aquariums (AZA), elephants are important conservation ambassadors for their species and ecosystems. Seeing, hearing and even smelling these magnificent animals up close in zoos is critical to helping visitors make an emotional connection to the natural world of elephants and take action to help protect their future. To save elephants, scientists need easy access to the animals to study them. Zoos provide an unparalleled opportunity for this.

Today the National Elephant Herpesvirus Laboratory at the Smithsonian’s National Zoo is the prime worldwide resource of herpesvirus information, testing and research for the global elephant community. The lab works in collaboration with Johns Hopkins University and focuses on diagnosing elephants in North America and researching new methods of testing for the various strains of elephant herpes. Its ultimate goal is to prevent future deaths resulting from this devastating disease. Genetics research at the Zoo is also focused on understanding EEHV and the family of genes that helps determine how resistant elephants are to infectious diseases, including tuberculosis and the herpes virus. The Zoo’s elephant herd has been actively contributing regular blood samples to this research effort.


To date, scientists have identified 14 genetically different elephant herpesviruses (EEHV), most of which are known to cause hemorrhagic disease. The viruses found in symptomatic elephants at different zoos and other institutions are genetically distinct, which means that they are not all the same strain spread by the transfers of elephants between and among zoos. The most common cause of acute EEHV cases and deaths in elephants is the EEHV 1A strain.

Herpesviruses are widespread in all vertebrate taxa, including humans. While herpesviruses are usually species specific, they can affect closely related species. (EEHV does not pose a health risk to humans, though humans are host to their own strains of herpesviruses). All herpesviruses do share common some features. Once inside a host, the virus can go into a latent (hidden) phase after causing only mild symptoms or no signs of disease at all. Scientists do not yet know where in the body EEHV resides during the latent phase.

For reasons unknown, an elephant herpesvirus can come out of latency and circulate throughout the bloodstream, causing disease. This is the only time when a herpesvirus can be readily detected in blood samples. Reliable tests are not yet available to detect a latent infection. Most elephants are able to fight the virus and survive when it comes out of latency. Calves appear to be most susceptible to EEHV disease after they have been weaned, at a time when they are not protected by their mother’s antibodies. 

There is no true cure for herpesviruses in animals or in humans. Based on current knowledge from ongoing research and from elephant care institutions that have experienced EEHV infections, the treatment protocols continue to improve, and detection and treatment recommendations continue to evolve.

Current antiviral treatments may suppress EEHV, and elephants can potentially recover if diagnosed and treated early. Of the elephants that have been treated, the success rate with anti-viral therapy against EEHV has been about 40 percent. To date, antiviral drugs have been used successfully in treating nine Asian elephants in North America. Veterinarians and scientists continue to collaborate to better understand this disease and develop more effective treatment options. 

EEHV is not just a disease of Asian elephants in human care in western countries. More than a dozen cases of EEHV have been identified in elephant populations in India and Cambodia. Moreover, these deaths only represent the cases in which necropsies were conducted in sufficient time to detect it.

Current research indicates that the elephant-specific herpesvirus may have been in elephant populations for tens of millions of years, just as human herpesviruses have been in human populations. Since this is a naturally occurring disease, every elephant in the wild and in human care probably carries one or more forms of elephant herpesvirus within them. 

Many animals and humans carry herpesviruses throughout their lives and never become ill. What researchers don’t know is what triggers the virus to become active and where exactly in the body the virus hides in its latent (hidden) phase. We don't know why some animals become ill and others don't. It's important to understand that it's not about who has the virus, but who gets ill and when. When they get the disease does seem to be important; calves who are nursing rarely get EEHV, so maternal antibodies seem to be important in protecting the calf from acute EEHV disease.

There is not enough research to confirm how EEHV itself is transmitted, but most viruses are normally spread from one individual to another. Viral shedding occurs when it comes out of latency (hiding); however, there is no simple way to detect if the virus is active without a blood test. What we do know is that every elephant—in the wild and in human care—probably carries one or more forms of herpesvirus within them. 

No. Like all mammals and humans, elephants carry a variety of different herpesviruses throughout their lives, and the majority of them may never cause illness, likely remaining latent (hidden). Some cause mild disease and some cause severe disease or death. Claims that certain zoos are contaminated once an animal becomes ill from EEHV are unfounded and based on a lack of understanding of how the viruses live within their hosts. Having a herpesvirus is the norm, not the exception. Like many viruses, herpesviruses cannot live very long outside the body, so a herpes outbreak does not “contaminate” a facility. 

To date there has been no evidence found of shedding of virus into semen or transmission of EEHV through natural breeding or artificial insemination. The Zoo currently follows the AZA Elephant TAG/SSP (Taxon Advisory Group and Species Survival Plan) which recommends that institutions continue to exchange elephants and elephant semen for breeding and artificial insemination as specified in the breeding recommendations. 

Cessation of breeding elephants in human care is not the solution to eliminate EEHV or to ensure the survival of elephants. Infectious diseases, including EEHV, are only one of many threats to the survival of elephants. Efforts to save the species cannot be undermined due to fears from a single, potentially manageable problem. Instead, continued studies and research are the tools to better manage the disease, prevent it and control its spread to ensure the continued survival and conservation of elephants. When an outbreak of equine herpes occurred in 2005 in horses, the industry did not shut down. Instead it funded research that resulted in treatment, prevention and control of that disease. When black-footed ferrets were nearly driven to extinction in the 1980s in part from canine distemper, we did not stop breeding them. U.S. Fish and Wildlife Service, AZA institutions, private landowners, conservation organizations, and other groups collaborated on a rescue and recovery program. An effective vaccine was developed and the species bounced back from the brink of extinction. 

While there are no guarantees as to the fate of a future elephant calf, Smithsonian's National Zoo experts have operated for many years under the conservative assumption that all the elephants in the Zoo's care could have one or more latent (hidden) herpesviruses. The risk is no higher or lower for an elephant born here, in the wild or at another zoo or sanctuary. Zoo researchers will continue to gather the evolving research and use the latest information to guide decisions in caring for the herd. If animal keepers see any signs of illness caused by elephant herpesviruses in one of the elephants, Zoo experts would institute immediate treatment, relying on the strong body of knowledge acquired since they first discovered this disease in 1995. 

The main test done at the EEHV lab is  called PCR (polymerase chain reaction); it looks for DNA from EEHV in blood from sick elephants or tissues from dead elephants and new births. Researchers use this to diagnose an active case of EEHV or to look for shedding of the virus when it comes out of latency (hiding). Zoo scientists consult with researchers around the world and help set up labs in other countries so that more research can be done, on both elephants in human care and in the wild. Some current research projects include determining the prevalence of the virus in range countries, subtyping the virus from cases to determine transmission and epidemiology of the viruses, determining the prevalence of the virus in different tissues and fluids, and improving on the diagnostic assays.

Yes, Zoo researchers have collaborated with researchers in Germany, the Netherlands, the United Kingdom, Thailand, Australia, India, Sri Lanka and South Africa on various projects and have shared protocols, samples, reagents, and expertise and provided equipment and training for their labs. 

Because herpesviruses go latent, we won't be able to find a "cure," but we hope to collaborate in refining effective treatments and help in the development of a vaccine to prevent EEHV. An important first step is to culture the virus. 

The National Elephant Herpesvirus Laboratory at the Smithsonian's National Zoo is dedicated to investigating this set of diseases, to understanding how to protect elephants in zoos, to solving the mystery of how EEHV is spread, and to developing an effective vaccine for the virus.

The collaborative work that zoos are doing to better understand EEHV may have important implications for wild elephants in the future. Wildlife biologists may one day need to draw upon the growing body of work and knowledge generated by zoos and the international elephant community to contribute to the long-term survival of the species in both zoo and wild populations.