There are many questions about this complex group of viruses. These questions and answers will help you better understand these viruses and the diseases they can cause.
To date, scientists have identified 14 genetically different elephant endotheliotropic herpesviruses (EEHV), five 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 (hidden) 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.
We conduct two main tests at the EEHV lab. The first, called PCR (polymerase chain reaction), looks for DNA from EEHV in blood from sick elephants or tissues from dead elephants and new births. We use this to diagnose an active case of EEHV. The second, called ELISA (enzyme-linked Immunosorbent Assay) looks for antibodies to EEHV in the serum of elephants and is used for research purposes—to track which elephants have been exposed to EEHV at some point in the past. We also consult with researchers around the world and help set up labs in other countries so that more research can be done, both on captive and wild elephants.
Our current projects include:
Serological testing means the testing of serum, which is the liquid portion of a blood sample after it clots. In our case, it means testing of elephant serum for the presence of antibodies to EEHV 1a—a specific strain of EEHV.
As mentioned above, we do a test, called PCR (polymerase chain reaction) to look for DNA from EEHV in blood from sick elephants or tissues from dead elephants and new births. We are able to use this to diagnose an active case of EEHV or provide a postmortem cause of death.
In August 2010, researchers at Baylor Medical College developed a real-time PCR test in collaboration with Gary Hayward and the National Zoo to detect EEHV 1 and 3. This new assay makes it possible to diagnose a case of EEHV faster and it is more sensitive, so that the virus can be detected even before symptoms begin to show We can also use it to track shedding of the virus, which will help answer questions about transmission and epidemiology of the disease. The National Zoo aims to have a real-time PCR test in place by early 2011.
Yes, we have collaborated with researchers in Germany, the Netherlands, the UK, Thailand, Australia, India, Sri Lanka and South Africa on various projects and have shared our protocols, samples, reagents and expertise and provided equipment and training for their labs.
We know that EEHV is not just a disease of the captive Asian elephant in western countries. According to an International Elephant Foundation progress report of spring 2009 by EEHV experts, more than a dozen cases of EEHV have been identified in elephant populations in India and Cambodia—eight wild Asian elephant calves died within the past year. 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 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.
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; 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.
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 National Zoo currently follows the Association of Zoos and Aquariums' Elephant TAG/SSP, which recommends that institutions continue to exchange elephants and elephant semen for breeding and artificial insemination as specified in the breeding recommendations.
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. 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.
There is no true cure for herpesviruses in animals or in humans. Based on current knowledge from our 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 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, and seven of the most recent eight elephants to get sick from EEHV have recovered with treatment. Veterinarians and scientists continue to collaborate to better understand this disease and develop more effective treatment options.
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.
Cessation of captive breeding is not the solution to eliminate EEHV or to assure 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, institutions accredited by the Association of Zoos and Aquariums, 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 we have no guarantees as to the fate of a future elephant calf, we have operated for many years under the conservative assumption that all our elephants at the National Zoo 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. We will continue to gather the evolving research and use the latest information to guide our decisions in caring for our herd. If we see signs of illness caused by elephant herpesviruses in one of our elephants, we would institute immediate treatment, relying on the strong body of knowledge acquired since we first discovered this disease in 1995.
The National Elephant Herpesvirus Laboratory at the National Zoo is dedicated to investigating this set of diseases, to understanding how to protect elephants in zoos, and to solving the mystery of how EEHV is spread and 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.
Posted April 2011