Equine Infectious Anemia: Symptoms and Control

Equine Infectious Anemia: Symptoms and Control

The strongest weapon against EIA is a test developed by Leroy Coggins, DVM, of Cornell University in 1970. The test carries his name, and the "Coggins" test is a household term in the horse world.

Photo: Erica Larson, News Editor

Equine infectious anemia (EIA) is a disease most horse owners know instantly by name because they must prove that their horse doesn't have it if they want to go to a show, sell it at auction, or even travel to another state. Yet, it would be fair to say that many of those same owners don't know what is involved with the disease--how it is transmitted, its history in this country, and what is involved if a horse tests positive for EIA.

In fact, says retired practitioner M.B. Teigland, DVM, of Miami Shores, Fla., a former American Association of Equine Practitioners (AAEP) president, many of today's younger veterinarians have never seen a case of EIA and might have trouble recognizing it if they did see it.

During the early 1900s, the disease was known as swamp fever because it was mistakenly believed that it existed only in wet, humid areas of the South. However, horse owners were to learn that altitude and climate posed no barriers to the virus causing the disease, and it was found to exist virtually all over the United States.

The strongest weapon against EIA is a test developed by Leroy Coggins, DVM, of Cornell University in 1970. The test carries his name, and the "Coggins" test is a household term in the horse world.

Clinical Signs

"EIA," says Dwight Bennett, DVM, PhD, professor emeritus at Colorado State University, "is a disease of horses, donkeys, and mules caused by a virus closely related to the human immunodeficiency virus (HIV). The disease is characterized by fever, anemia, jaundice, depression, edema, and chronic weight loss."

EIA should be suspected in any horse with a history of recurrent fever or weight loss, Bennett says.

Members of the equine family are the only animals successfully attacked by the EIA virus. The disease is spread by biting insects, such as horse flies and deer flies.

The disease is a virtual death sentence for the horse contracting it. In many cases, the disease is so severe that it kills the horse. If the horse recovers, it will test positive for the malady for the rest of its life, and "positive" horses are generally euthanatized on the spot or sent to slaughter.

Unfortunately, horses can also carry the virus without showing clinical signs.

The clinical signs that Bennett described are a result of inflammatory and immune responses to the virus. Following is Bennett's description of how EIA virus functions: "In the case of EIA, the virus attaches to various cells in the horse's body. In response, the horse's system produces antibodies, which are never completely successful in eliminating the virus. Instead, they inadvertently attack the cells with viral particles attached, with resultant damage to the kidneys, liver, spleen, lymph nodes, bone marrow, and brain. The anemia is due to destruction of the red blood cells within the body, and the jaundice is due to the accumulation of the products of red blood cell destruction in the tissues.

"Manifestation of EIA in horses first exposed to the virus can be acute," he continues. "The severity depends on the dose and virulence of the virus, the resistance status of the horse, and the degree of environmental stress. Symptoms vary from mild fever and depression to very severe conditions that result in death within a few days. A most troublesome feature of EIA is that once a horse is infected, it remains infected for the rest of its life."

There is no successful way to treat EIA, and there is no vaccination against it.

Chronic Infection

Chronically infected horses that have survived the initial effects of the disease can go for years without showing clinical signs or anemia, Bennett says. However, a variety of stress factors can cause the virus' effects to resurface. Included in that category, according to Bennett, are hard work, transportation, adverse environmental conditions, occurrence of other diseases, or reactions to certain drugs, such as corticosteroids.

There are no laws or regulations that say the only option for a horse testing positive for EIA is euthanasia, but practical considerations often leave it as the only viable alternative. When a horse tests positive, that fact must be reported to state and federal agencies and the horse must then either be euthanatized or quarantined for life so that it does not come into contact with other horses. For most horse owners, a lifelong quarantine for the horse is not an option.

Persistence and Prevalence

While the Coggins test and an even more accurate CELISA test have been instrumental in stopping the spread of EIA, the disease has not been eliminated. Although only a fraction of 1% of the horses tested each year show up as carriers, the virus stubbornly hangs on.

It wasn't all that long ago, recalls Teigland, when the disease was doing much more than just hanging on. In the 1960s and before, there was no definitive test and, to make matters worse, the equine population in some areas--particularly Florida--was under attack by piroplasmosis, a disease that mimicked EIA. In many cases, veterinarians weren't sure which of the two they were dealing with because there wasn't a definitive test for piroplasmosis, either.

About the only way veterinarians had of differentiating between piroplasmosis and EIA, Teigland says, was to administer tetracycline. Horses with piroplasmosis often had a positive response to the drug, while horses with EIA did not.

Because EIA was so prevalent in Florida in the early 1960s, Teigland says, many veterinarians became adept at correctly diagnosing it. "It got so that we felt we could diagnose it on the spot," he says. "You could smell it."

The late General Wayne O. Kester, executive director of the AAEP for many years and author of a history covering the early years of the organization, discussed EIA in his published account of the development of the organization. In a December 1965 letter to the president of the National Association of State Racing Commissioners, which was published as part of the AAEP history, Kester had this to say about EIA: "EIA is not new, and it is not a disease of the Southland. The fact that the mosquito and possibly the horse fly are believed to be the normal vectors explain both the name swamp fever and why the disease once appeared to be more prevalent in the coastal areas. It was widespread in most states in the early 1920s.

"We saw outbreaks in army horses at the Fort Robinson, Neb., Remount Station, as well as elsewhere," Kester wrote. "It was beginning to immobilize horse and mule power in the Cotton belt when the farm tractor came to the rescue 40 years ago. It was recognized as a national problem and the USDA did extensive research until 1930. It 'faded away' only because the reservoir of horses 'faded away.' When the horse returned as a pleasure animal in recent years and spread out over the country, the disease soon followed."

One of the first groups to take up the cudgel against EIA was the American Quarter Horse Association, which financed research at Texas A&M University aimed at developing a definitive diagnostic test.

The Texas A&M researchers developed a test that Kester described as being 98% accurate. However, it did not receive USDA approval and never gained widespread use in the field.

A resurgence of EIA in the early and mid-1960s brought near-panic to the horse industry. There were outbreaks at three racetracks, and the fear was that the disease would run rampant throughout the country's horse population.

The three tracks that EIA attacked in 1965 were Arlington Park and Fairmount in Illinois, and Longacres across the country in Washington. No one knew quite how to handle the situation. Neither the USDA nor most state regulatory agencies had the authority to implement control measures.

Kester outlined the problems that faced the veterinary community in regard to EIA:

"There is no practical test that a veterinarian may request or use to confirm his diagnosis. Only in very recent months has the Texas test become available.

"EIA is not specifically a required reportable disease in some states," Kester stated. "Further, in states where it is required, a veterinarian is reluctant to report a disease which he cannot positively diagnose and cannot produce laboratory evidence to support his opinion. Further, many practitioners have learned the hard way that diagnosing and reporting the disease is often unwise and seldom constructive. Some have promptly found themselves in disfavor with clients, ostracized by officials, and generally regarded and sometimes treated as an unwelcome criminal for having diagnosed and having brought up the ugly problem of swamp fever.

"Veterinarians have also learned that frequently following a tentative diagnosis of EIA, suspected horses are promptly sold and disappear. Whole herds of infected horses have been dispersed, thus further spreading the disease. There is no enforceable law and no means of preventing such transactions. Even now, with the (Texas) test available, there is no requirement that it be used, and when it is suggested that a horse be tested, the owner may find it more expedient to sell the animal than to submit to the test.

"EIA will not be brought under control, or the problem even approached to anyone's satisfaction, until an accurate and practical test is available that will definitely establish whether a horse is or is not infected or a carrier of the disease," concluded Kester. "Further, this test must be recognized by the USDA as the official test. Then, and only then, will the disease be brought under control."

Kester's comments in that concluding paragraph were prophetic. There was little progress against EIA during the next five years, although conferences were held, research continued, and efforts were made to both prevent and treat EIA. Some guidelines for dealing with EIA were established, thanks to seminal efforts by the AAEP, but a definitive test still remained tantalizingly just beyond the grasp of researchers.

Then came the breakthrough in 1970 with the Coggins test. Now, a definitive diagnosis could be made. USDA quickly approved the test, and one state after another followed suit. Rules and regulations were established concerning the movement of horses--basically, horses couldn't cross state lines unless they had first been tested for EIA. Horse shows, race tracks, auctions, and other venues stipulated that horses would not be permitted on the grounds unless the owner or trainer had in his or her possession a negative Coggins test for that particular horse.

"Once we had the diagnostic test," Teigland says, "we had the battle won."

Thanks to the Coggins test, EIA has been brought to its knees, but it has not been stamped out. The virus still exists and shows up year in and year out in a few horses. Some have advocated the cessation of testing, but others, such as Bennett, urge continued testing as an effort to prevent the disease from ever gaining a strong foothold again.

Today, all 50 states have rules in place concerning EIA. Some require that all horses that cross their boundaries be accompanied by a negative test. Others set the age at six months before a test must be administered. Still others do not require a test on nursing foals, providing the dam has tested negative.

Some states require horses crossing their borders to be tested every six months. About an equal number require administration of the test on a 12-month basis. One state--Hawaii--requires a negative test within three months of entry.

The implementation of these regulations through the years has resulted in a depopulation of infected horses either through slaughter or euthanasia.

Today, says Teigland, few veterinarians see EIA. "I'm sure," he says, "that many of today's young practitioners have never encountered a case of EIA and wouldn't know what it was if they saw it."

That is exactly as it should be. And if the horse population is fortunate, it will remain so. 

OPTIONS FOR AN EIA-POSITIVE HORSE: Equine Infectious Anemia (EIA) Farms

If your horse is diagnosed with EIA, euthanasia is not your only option. One farm in southern Florida is devoted to the care of EIA-positive horses. The Florida Research Institute for Equine Nurturing, Development, and Safety (FRIENDS) opened in 1970, became a not-for-profit organization in 1987, and serves as a safe haven for horses diagnosed with EIA that would otherwise be sent to slaughter or euthanatized.

Currently, 51 horses live there; 48 are "A" branded and under EIA quarantine. Three horses there serve as sentinels for EIA and are turned out in the pasture with EIA-positive horses. Amazingly, these horses are negative on official ELISA-based tests, as well as on a research immunoblot test and an AGID (agar gel immunodiffusion, or Coggins) test.

Chuck Issel, DVM, MS, PhD, Dipl. ACVIM, a researcher at the University of Kentucky's Gluck Equine Research Center, uses the horses at FRIENDS to obtain blood samples to study EIA. It is FRIENDS' policy to allow researchers to draw blood samples from the horses at the farm in order to continue progress towards a vaccine and/or cure for EIA.

"EIA test-positive horses maintained and used at FRIENDS provide a unique opportunity for us to document in natural infections EIA virus presence, quantity, and anti-mutation changes, as well as to monitor the antibody against EIA virus in approved and research tests over time," Issel says. "The ultimate goal (of research) is to define a vaccine for EIA that would be effective in the field where challenges with diverse strains of EIA virus are expected."--Marcella M. Reca

COMPUTERIZED PAPERS: Electronic EIA Forms Now Available

Online EIA submissions and health certificates have become more popular, and they answer a need as the horse industry looks toward animal and premises identification.

"The world is moving toward animal identification and trace-back in less than 48 hours," says Kevin Maher, president of GlobalVetLink. "It is not possible to accomplish that with the current paper system." GlobalVetLink (GVL) developed the nation's first web-based health certificate system used by state, federal, and accredited veterinarians. The system allows practitioners to create health certificates that include EIA test requirements for movement.

Practitioners access a secure online database tied to their accreditation license, and they can automatically submit requests for EIA tests to their diagnostic lab with much less paper and hassle. Results back to practices cut out seven to 10 days turnaround time, plus saves on paper, mail, and other administrative costs. Copies automatically go to appropriate state animal health officials who, along with veterinarians, can verify any online document presented at shows, events, and exhibitions.

Horse owners get online EIA certificates from their veterinarians. They are signed in ink, and they can include all methods of identification as well as digital pictures.

To learn more, see www.globalvetlink.com.--J. Amelita Facchiano

About the Author

Les Sellnow

Les Sellnow is a free-lance writer based near Riverton, Wyo. He specializes in articles on equine research, and operates a ranch where he raises horses and livestock. He has authored several fiction and non-fiction books, including Understanding Equine Lameness and Understanding The Young Horse, published by Eclipse Press and available at www.exclusivelyequine.com or by calling 800/582-5604.

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