Odds On Racing - Harness Racing

EIA—Swamp Fever & the Coggins Test
The history of the deadly disease and modern testing applications

By Kimberly A. Rinker

In Walter Farley’s book, "The Black Stallion & Satan," the Black and his Triple Crown winning son Satan become exposed to a horse stricken with the deadly disease known as Swamp Fever—or Equine Infectious Anemia (EIA). His owner Alec and trainer Henry must then face the possibility of losing their prized and beloved racehorses.

"…the disease can reach epidemic proportions if not controlled. It is transmitted from infected horses to healthy animals by flies and mosquitoes or through stable equipment such as combs, brushes, saddles, bridles, blankets and anything else which may have touched an abrasion of the infected horse and is then used on a healthy animal…"
---Chapter 13, entitled The Silent Killer, from "The Black Stallion & Satan"

Farley’s book was published in 1949, a good 31 years before Dr. Leroy Coggins of Cornell University developed the first laboratory test for detecting the disease in 1970. The Coggin’s test—as it was christened—was made the official test for EIA by the United States Department of Agriculture in 1973. Up until Coggins developed his famed test, it was, as Farley wrote, believed that Swamp Fever was transmittable through a variety of means. It is now a fact that equines and their relatives can only contract this disease through the blood.

"…the only definite way we have of finding out is to take blood samples from your horses and, pooling this blood, inoculate it into the bloodstream of a horse who has not been exposed to this disease. If no evidence of the disease appears in the inoculated test horse, your horses will be given a clean bill of health and released…"
---Chapter 13, entitled The Silent Killer, from "The Black Stallion & Satan"

Swamp Fever, or EIA as it’s known to most horsemen today, has been around for centuries, and cases have been reported throughout the globe. Horses, ponies, mules and donkeys are all at risk, and once infected, they are infected for life. The first official case was recorded in France in 1843 and in the United States the first case was reported in Wisconsin in 1888. Likewise, the disease was first confirmed in Canada in Manitoba in 1881, and a single case has been reported in New Zealand.

During the last century, two major outbreaks occurred in North America: in 1901 Wyoming suffered a horrific epidemic and in 1947 New Hampshire’s Rockingham Park became the site of an outbreak that resulted in 77 horses being euthanized or dying.

"…Despondently all the men raised their hands. No questions were asked. No word was spoken. The cancellation of the race to which they had looked forward for so many months was of no importance now to any one of them. Instead, each was haunted by the fear that his horse might be stricken…that before long he, too, would have to consent to the destruction of his horse. They were the trainers of the world’s finest horses…horses that in the years to come were to have passed on their speed to their get for the improvement of the breed. Now, they were to be exiled..."
---Chapter 13, entitled The Silent Killer, from "The Black Stallion & Satan"

Generally, EIA outbreaks have been sporadic throughout the United States over the years with the majority of cases occurring in what is known as the "insect belt" of the country (Texas, Oklahoma, Arkansas, Louisiana, Mississippi, Alabama, Tennessee, Kentucky, North Carolina, Georgia and Florida).

Dr. Gary Wilson, a Chicago-based equine veterinarian who has practiced on both the Chicago and Miami racing and show horse circuits says that positive Coggins tests, while rare, still do occur, although they are more likely to do so in the southeastern portion of the U.S.

"When I was working in Miami on horses from 1980 through 1984 we had two or three positive tests per year," Wilson, 53, noted. "I really never thought I’d encounter Swamp Fever after vet school. However, after coming to the Chicago area, I’ve only witnessed three positive Coggins tests in 18 years of practice, and they were all on racetrack horses, no show horses."

"…The State Veterinarian cleared his throat. ‘I know the difficult time that is ahead of you, gentlemen. We appreciate the full cooperation you have promised us. We hope, as you do, that none of your horses will be found to have Swamp Fever and that clean bills of health will be given to all’…"
---Chapter 13, entitled The Silent Killer, from "The Black Stallion & Satan"

Understanding the disease can be both complicated and frustrating for research teams trying to develop a vaccine or treatment procedures against EIA. The EIA virus is a slow-acting virus of a family of viruses known as the "lenti-retrovirus group." These types of viruses are also responsible for the AIDS (acquired immune deficiency syndrome) in humans, as well as leukemia in cats, mice and cattle.

These viruses will attack organs such as the spleen, liver, kidney and lymph nodes, where they basically take over a cell and wait to become activated, upon which time they reproduce to the point of infecting more cells. This is why a horse will suffer reoccurring symptoms. The virus is able to change its protein content (like the AIDS virus can) to accommodate which organs it attacks, thus, the reason for making the production of a solid vaccine extremely difficult.

EIA is not transferable to human beings and is not directly contagious from one horse to another—in other words, it can only be spread through contaminated blood. Contrary to what most horsemen believe, EIA is transferred mainly by horse flies, stable flies and deer flies—not by mosquitoes. The reason being is that mosquitoes are less likely carriers because of the amount of contaminated blood that is left on their feeding apparatus is not typically enough to support the EIA virus. Mosquitoes feed on the same animal usually, and even when their feeding is interrupted, they continue to stay on the host animal.

Horse flies, especially, are considered the highest risk carrier of EIA. Horse flies, due to their larger size, their noise and their painful bites, will often be interrupted when feeding on a horse, and are likely to travel a close distant to another animal. Their feeding apparatuses are considerably larger than other carriers, and contain sufficient amounts of blood that can be transferred from one horse to another. However, according to the Penn State College of Agricultural Science department, research has shown that flies are unlikely to travel more than 200 yards when feeding. As a result, when horses are quarantined for EIA, the USDA mandates the minimum distance is 200 yards for keeping infected individuals apart from healthy animals.

"…Suddenly the Black threw back his head, almost breaking the lead shank. Alec’s hand went to the halter. As he held him, he realized the stallion had felt the sharp prick of the needle. But that would be all there was to it. It was over now…"
---Chapter 15, entitled Small, Worried World, from "The Black Stallion & Satan"

The Coggins test is called an AGID test—or "agar-gel immunodiffusion test. This test defines antibodies in the blood—not the actual EIA virus, and has a 95% efficiency rate. If EIA antibodies are present, it means that the horse has likely been infected with the virus. If the test comes back positive, it is usually imperative that another blood sample will be taken again, this time using the hyper-sensitive ELISA and Western Blot tests.

The ELISA (enzyme-linked immunosorbent assay) test examines the body’s immune response to EIA, while the Western Blot test determines the body’s immune response to specific EIA-related particles. To be reported as positive by the ELISA test, two of three tests on the same blood sample must be positive. However, the ELISA test—no matter what the results—are usually always confirmed with the more specific Western Blot test. The Western blot test is less sensitive than the ELISA test but it hardly ever gives a false-positive result. It is important to note as well that the Western Blot test is always used to test positive ELISA test results.

Most racing jurisdictions require that each horse have a current (within 12 months) Coggins test on file with that jurisdiction’s racing secretary. Likewise, most horse show circuits and sale companies require a copy of a negative Coggins to accompany their entry slips—some requiring that the test be no less than two weeks to six months old. Trainers entering horses in events are often denied the right to race or show without a negative, current Coggins test or proof thereof.

In closing, it must be noted that despite all the years of research and countless studies, there is still no known treatment or vaccine for EIA. For infected horses, there is little hope and no options. The horse must be either destroyed, or branded and quarantined for life.

The Coggins test is still considered by most veterinarians to be the only effective way to combat the virus. Through identification and control, horses infected with EIA has been and will continue to be the only key to prevention until a vaccine or appropriate treatment plan can be discovered and implemented.

"…now that the haunting fear of swamp fever was a thing of the past, each owner and trainer talked only of the speed of his horse…of Sea King and Kashmire, of Avenger and Phar Fly, of Cavaliere and Satan. For many hours they discussed the race that had never been run and what might have happened…
---Chapter 16, entitled Trapped!, from "The Black Stallion & Satan"

The Red Mile Scare
In the fall of 2004, horsemen racing at the Red Mile in Lexington endured a scare of the possibility of EIA contamination. The horse JJ’s Ironman won on October 6 at the Red Mile, and had raced with a negative Coggins test that had been taken on April 8, 2004, but needed a new test since he was set to travel to Canada for the Breeders Crown.

However, an ELISA test taken just after his victory at the Red Mile came back positive on October 8, and prompted the quarantining of not only JJ’s Ironman, but 37 horses housed in three barns at the Lexington raceway. This doused the hopes of some possible Breeders Crown contenders who were then forced to remain at the Red Mile in quarantine, under Kentucky Department of Agriculture regulations.

JJ’s Ironman was then given the Western Blot test at the University of Kentucky Livestock Disease Diagnostic Center, Gluck Equine Research Center. While the results for the original ELISA kit were positive, two additional ELISA tests were negative, and JJ’s Ironman then tested negative to the Western Blot test. The result was that the 37 other horses under quarantine who were tested on October 13 were subsequently reported negative and released and allowed to travel to other destinations.

Robert Stout, DVM and Kentucky State veterinarian, issued this statement: "After reviewing the history, results of the diagnostic testing, and in consultation with research and epidemiologic specialists, it was concluded that the index horse (JJ’s Ironman) is not infected with EIA, and there is no evidence to suggest recent exposure. Explanation for the positive ELISA reaction and the inconsistent reactivity noted in the AGID tests will be pursued. The index horse is deemed negative for EIA, and the quarantine has been released."

Three forms of Equine Infectious Anemia (EIA)

Acute: The horse shows heightened affection of the disease with clinical signs of depression and fever (short-lived) and anorexia. Typically, this type of EIA ends in death that occurs in two to three weeks after the initial symptoms.
Chronic: The horse goes through cycles of the disease at reoccurring intervals (usually every two weeks), each time with signs of edema in the legs and stomach region, high fever (105-108), weight loss, and anemia. Possible death generally occurs four weeks after the initial symptoms have surfaced in the animal.
Inapparent Carrier: If the horse has not died during a chronic bout with EIA, he or she will become known as an Inapparent Carrier. This horse will show no signs of the illness, but simply becomes a carrier of the disease. However, the horse can lapse into the acute or chronic phases of the ailment at any time.

The United States Department of Agriculture states that:

One milliliter (1/5 of a teaspoon) of blood of a horse infected with acute illness of EIA contains enough virus to infect one million horses
One milliliter (1/5 of a teaspoon) of blood of a horse infected with chronic illness of EIA during a feverish episode contains enough virus to infect 10,000 horses.
In an inapparent carrier, only one horsefly out of six million horseflies is likely to pick up and transmit EIA from a horse.

The Three Tests at a Glance:

The Coggins test--AGID (agar-gel immunodiffusion test). This test defines antibodies in the blood—not the actual EIA virus, and is 95% reliable
The ELISA test--(enzyme-linked immunosorbent assay) examines the body’s immune response to EIA. Taken when a Coggins test comes back positive. There will typically be two to three tests taken from one blood sample for the ELSIA test.
The Western Blot test--determines the body’s immune response to specific EIA-related particles. Used to confirm a positive ELSIA test and rarely gives false-positives.