Your Horse’s Coggins Test

When you take your horse on the road, a negative Coggins test for equine infectious anemia is especially important — and often required. Here’s what you need to know about this killer disease.

Credit: CLIXPHOTO.COM It’s important to get a Coggins test for your traveling horse, as movement of infected horses to new areas is how EIA can travel long distances.

What if you knew of an equine disease that had no cure, no treatment, and in many cases would require you to destroy your horse if he became infected? You’d probably find that pretty scary.

Well, such a disease does exist, but luckily, it’s rare enough that we tend to forget about it. Because the Coggins test has proved so effective, equine infectious anemia (EIA) receives very little attention these days. But it’s still around, and it’s still a killer.

Credit: Betsy Lynch Although it has become relatively rare, EIA is an insect-borne disease, so it’s hard to protect horses that are constant targets of biting flies. As yet, there’s no effective vaccine or treatment for this potentially fatal disease.

Here, I’ll first go over the causes of EIA and explain how the virus spreads. Then I’ll tell you why getting a Coggins test for your horse is so important, especially if he’s on the road.

How EIA Spreads

Also known as “swamp fever,” EIA is caused by infection from a lentivirus, the same family of virus that causes acquired immune deficiency syndrome (AIDS) in people. However, people can’t get AIDS from the equine virus, nor can horses get EIA from the human virus.

EIA can’t be spread by casual contact. It’s usually transmitted via large biting flies, which carry virus-packed blood from an infected horse to a neighboring horse.

Although transmission through sexual contact has never been documented, the virus has been known to show up in semen. Passage of virus in saliva and manure is also a possibility.

People can spread the infection by using the same needle or dental instruments with blood on them on different horses.

Movement of infected horses to new areas is how EIA can travel long distances, as the biting flies don’t travel far. As yet, there’s no effective vaccine or treatment for this potentially fatal disease.

EIA Symptoms

An infected horse may be symptom-free for a long time, until some stress (such as another infection, shipping, hard exercise, etc.) weakens his immune system and the virus becomes activated. Other horses may never show they have the infection and are called inapparent carriers.

EIA hides inside a type of white blood cell (macrophages) that carries it throughout the horse’s body. Highest concentrations are usually in the lymph nodes and lymphatic system, liver, spleen, kidney, and bone marrow, but it can go to any organ, even causing The symptoms of EIA infection are only evident when the virus is active. Fever is the first sign, but it’s easily missed. The next symptom is usually anemia, which occurs because chemical-signaling molecules become attached to the red cells and trigger the immune cells to engulf the cells. This causes weakness, depression, poor oxygen delivery, and possible organ damage.

Credit: Bob Langrish A simple blood test, called a Coggins test, can determine if a horse is a carrier of equine infectious anemia.

As the disease progresses, problems with clotting appear because the platelets are destroyed. The white cell numbers also start to decline. Eventually, the liver and other organs become damaged. The horse slowly but steadily loses weight, showing swelling (edema) of the belly and legs.

If EIA isn’t suspected, the horse will probably be treated with dewormings, dietary changes, and antibiotics, but none of these things help. Once horses become symptomatic, they show a slow but steady wasting away until the disease itself kills them or they’re euthanized.

The Coggins Test The first step in diagnosis is the Coggins test, a blood test that detects antibodies to the EIA virus. When this is positive, two more specialized and more sensitive tests are done to make sure the diagnosis is correct.Since Leroy Coggins, DVM, developed the test in 1970, cases of EIA have dropped dramatically. Governmental agencies have taken drastic measures with positive horses, generally requiring euthanasia, though quarantine is sometimes allowed. Every state has laws regarding mandatory Coggins testing. While the laws vary a bit from state to state, they usually require testing of horses being shipped and competing in shows or races, as well as horses being sold at public auction.

Any horse that tests positive will have to either be destroyed or kept quarantined for the rest of his life.

The serious nature of the infection, the constant threat that horses with active infection pose to other horses, and the inability to treat it are why it’s considered so important to try to identify infected horses and remove them from contact with healthy ones.

Eleanor M. Kellon, VMD (, is a Staff Veterinarian for Uckele Health and Nutrition, Inc., and is the owner of Equine Nutritional Solutions, a nutritional consulting firm. An Honors Graduate of the University of Pennsylvania Veterinary School, Dr. Kellon completed her internship and residency in Large Animal Medicine and Surgery at the renowned University of Pennsylvania New Bolton Center. Her book, Horse Journal Guide to Equine Supplements and Nutraceuticals, is available on

Related Articles
HR_24BON Grooming Feature_01
Groom to Win
Grooming Secrets to Show Like the Pros
HR_24BON_Conformation Clinic_Performance-Mares_01
Conformation Clinic: Performance Mares
HR_24BON_Crabbe Dont Call it Maintenance_crabbe_01
To Inject or Not to Inject
Don’t Call It Maintenance! 
Palomino horse with long blond mane
Mane-tain Those Locks
Maximum Mane Care Tips
Receive news and promotions for Horse & Rider and other Equine Network offers.

"*" indicates required fields


Additional Offers

Additional Offers
This field is for validation purposes and should be left unchanged.