November 8, 2012
Recent cases remind us that testing for this horse-health threat is still necessary.
By Dr. Thomas Lenz in The American Quarter Horse Journal
In August 2011, a positive horse was detected on a ranch in Arkansas, which reinforces the need for testing. Subsequent testing of all horses on the property revealed that 40 of the 80 horses were positive for EIA. Of those, two died, and 38 were euthanized. The remaining horses were to be retested in 60 days to ensure that they had not contracted the disease.
EIA, first diagnosed in the United States in 1888, is caused by a virus usually transmitted between horses by blood-sucking insects.
The disease can only be transmitted to Equidae (horses, donkeys, mules, zebras, etc.), not humans. Approximately 5 percent of horses who contract EIA develop acute clinical symptoms, which include high fever (105 to 107 degrees F), depression and anemia and usually die within two to three weeks.
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The blood of acutely infected horses contains high numbers of virus particles, and so the horses are extremely contagious. An estimated 95 percent of EIA-infected horses do not develop acute symptoms, but rather become chronically infected.
The chronically infected horse might appear completely healthy, but act as a reservoir of the disease his entire life. However, the carriers might become acute and begin shedding due to severe stress, hard work or the presence of other diseases. Other chronically infected horses might become “poor doers” that lose weight, become lethargic, often develop edema (swelling) under their chest and lower legs, and periodically run a fever.
There is no vaccine or effective treatment for EIA.
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The Coggins test is named is named for Dr. Leroy Coggins, who developed it in the early 1970s. If a horse tests positive, he is segregated from healthy horses as soon as possible, and the premise is quarantined until all horses can be tested. Most regulations require that positive horses be euthanized or quarantined at least 200 yards from healthy horses for the rest of their lives. Many states require the quarantine area be a screened stall.
To reduce the risk of your horses contracting EIA, test all of your horses to ensure that they are not positive, and require a negative Coggins test for any horse entering the premises.
Use disposable syringes and needles when treating or vaccinating horses and never use the same needle on multiple horses. Implement insect-control measures and quarantine new arrivals for at least 30 days.
Dr. Thomas R. Lenz, diplomate of the American College of Theriogenologists, is a trustee of the American Horse Council, is chairman of AQHA’s research committee and is a past president of the American Association of Equine Practitioners.