Protecting Horses Against Equine Infectious Anemia
That annual Coggins test has been part of your routine as a horse owner for so long, you may not realize why it's important.
Equine Infectious Anemia (EIA), also referred to as "swamp fever," is a blood-borne infectious viral disease that affects equids around the world. First tentatively diagnosed in the United States in 1888, EIA surged during the 1960s and 1970s, infecting thousands of horses. According to the American Association of Equine Practitioners (AAEP),10,371 cases were identified in U.S. horses in 1975.
Although EIA remains a threat, thanks to widespread testing and surveillance, the number of positive horses in the U.S. today is minimal. The United States Department of Agriculture (USDA), the agency responsible for keeping track of EIA cases in the U.S., reports that out of 1,187,536 EIA tests conducted in 2018, only 51 horses tested positive.
Transmission of EIA
In some equine viral diseases, the disease actually replicates in the insects that transmit it. A good example of this is West Nile Virus, which is transmitted to horses by mosquitoes that have fed on infected birds. EIA is different in that the biting flies that typically spread it don't circulate the virus in their own bodies, but simply serve to "transport" infected blood from a horse that has EIA to a "clean" horse when feeding between nearby horses.
EIA is most commonly spread by biting flies, such as horseflies and deer flies.
"The reason horseflies are so effective as vector insects is that they can carry large amounts of blood on their mouthparts compared to other biting flies," says Todd C. Holbrook DVM, Diplomate ACVIM, ACVSMR. A board certified specialist in equine internal medicine, sports medicine and rehabilitation at Oklahoma State University's College of Veterinary Medicine, he holds the June Jacobs' endowed chair and is a professor of equine medicine at OSU. Holbrook has served as an international team veterinary consultant with the U.S. Endurance team for the last two decades.
If the horse fly's feeding pattern is interrupted, say, by the horse switching its tail, then the fly will immediately try to land on another horse close by to continue feeding. If the first horse is infected with EIA, the fly can transfer contaminated blood when it feeds on the next horse.
"It used to be that we knew where pockets of positive horses were based on untested herds and tracing back pockets of positive tests, but we don't now. The Gulf Coast states have always been EIA 'hotbeds' because of the insects, but positive cases have popped up in states that have traditionally been negative," notes Holbrook. "Nowadays the evidence is mounting that it's less connected with fly transmission than with iatrogenic (caused by humans) transmission."
Iatrogenic infection occurs when contaminated blood from an infected horse is introduced to a "clean" horse, by such inappropriate actions as sharing needles/syringes, re-using intravenous tubing, or other equipment, and incorrect handling of multi-dose drug vials, including inserting a used needle into the vial.
Because iatrogenic infection is completely avoidable by following standard precautions, it's all the more tragic when a horse is infected through human carelessness.
Testing for EIA
Until the Coggins test was developed to confirm the presence of EIA, a horse owner was only aware of the disease if their horse died, or showed clinical signs--something not all horses do.
Today, the Coggins test, also known as Agar gel immunodiffusion (AGID), remains the most widely accepted procedure for diagnosing EIA. Blood samples are submitted by an accredited veterinarian, state or Federal animal health official, and EIA tests are conducted in USDA-approved laboratories.
Since there's no such thing as "Coggins disease" (although some people have mistakenly referred to EIA this way), you may have wondered why this routine blood test is known as a "Coggins" test. For that, we can thank the late Leroy Coggins, DVM, a 1957 Oklahoma State University graduate, who developed a test for antibodies specific to EIA. Testing was initiated in 1972 and was quickly adopted by animal health authorities around the world.
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Here's a quick lesson on why continued annual testing is important for all horse owners. Let's say you're an avid trail rider who routinely haul your horse to ride the public trails in your state. This past weekend, after enjoying a great ride, you tie your horse to the trailer in the parking area at the trail head and join your friends for a picnic lunch there before heading home. Your trailer is parked near other trailers, where multiple horses are also tied.
Wide-spread testing and universal regulation have greatly reduced the spread of EIA and losses from the disease are negligible today. Although numbers have dropped significantly, even one owner being forced to euthanize their beloved partner because of a positive test is one case too many.
Do your part to minimize the risk of EIA:
- Continue annual Coggins tests for every horse
- Don't allow any horse on the property
- Use fly repellent and physical barriers such as fly masks to reduce your horse's exposure to biting flies
Protecting your horse against Equine Infectious Anemia (EIA) includes keeping up with the annual Coggins test and using diligent fly control to protect against biting flies that can transmit the disease. Build an effective No Fly Zone that includes the physical barrier of a fly mask, on-horse repellent products, and feed-through fly control.
Did you Know?
EIA is a "reportable" disease in the United States, meaning that any horse, pony, donkey, mule, (or zebra!) that tests positive must be reported to the USDA. Depending on the state, a positive equine must either be euthanized or kept permanently isolated in strict life-long quarantine away from other horses.