The Coggins test is a blood test used to diagnose the disease Equine Infectious Anemia (EIA), sometimes called swamp fever. EIA is a viral disease of horses and other Equidae such as ponies, mules, and donkeys. Once infected, the animal is infected for life. There is no effective vaccine and no known cure. When infected with the virus, the horse may develop a fever, be off feed, and possibly show some bruising of the mucous membranes. After recovering from the initial illness, some horses develop recurring cycles of the above symptoms that lead to the classic signs of anemia, weight loss, and ventral edema. The frequency and severity of these episodes decrease with time. Most horses do not die, but become asymptomatic carriers (i.e., animals with no signs of illness who are still capable of spreading the disease). Many horses that are infected will show few of these symptoms and quickly become asymptomatic carriers. These mild symptoms can easily be mistaken for other less serious diseases.
EIA is not contagious to people and is not directly contagious from horse to horse. It can only be spread via contaminated blood. The most likely way this occurs is via blood-sucking insects such as horseflies, deer flies, and less frequently mosquitoes. Since the virus only survives on the insect’s mouth parts for between 30 minutes and four hours, the insect must be interrupted while feeding on one horse and finish its blood meal on another to spread the disease. The virus can also be spread by blood contaminated needles or surgical instruments.
The Federal government does not require a Coggins test prior to the interstate shipment of horses, but it does require one before a horse can be imported. Most laws dealing with EIA are established at the state level. Almost all states require at least a health certificate and a negative Coggins test for a horse to enter the state. A few states require Coggins testing within the last six months, but most will accept results from the last 12 months.
Protecting a horse from exposure is the only way to prevent EIA. The Coggins test is a valuable tool in reducing the number of horses serving as a reservoir for insects to spread the disease. A federally accredited veterinarian fills out a form that positively identifies the horse. Blood is then drawn and sent to an accredited laboratory. The owner receives a certificate with recorded results. If the test is positive, the farm is quarantined and other horses in the area that may have been exposed are tested.
Several things can be done to help protect horses from exposure. These include:
- Testing all horses for EIA at least annually. Horses that travel in or come from areas where the incidence of EIA is higher should be tested more frequently. The Gulf Coast states have the greatest number of positive tests each year because the temperature and humidity favor a prolonged vector season.
- Stable owners should require a current negative Coggins test before introducing new horses.
- Horse show and event managers should require and verify all certificates. Enforcement of these rules is important.
- Needles or syringes should never be used on multiple horses.
- Apply topical insecticides during biting insect season.