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Every year, before the the start of the show season, you have to call the vet out to draw blood for a Coggins test. Not only that, but they take some nice pictures (or draw them) of your horse to put onto the Coggins certificate. A few days later you get back a paper stating that your horse was negative for Equine Infectious Anemia and you can go on your way. So what exactly is Equine Infectious Anemia and why do we need to test for it every year?

Equine Infectious Anemia is a viral disease of equids. It was first discovered in Europe in the mid 1800’s and was found in the US in 1888. It is caused by an aptly named virus – the Equine Infectious Anemia Virus. Someone spent a lot of time coming up with that one! This virus is similar in nature to Human Immuno-deficiency Virus (HIV). It can be transmitted through blood, saliva, milk and body secretions. In horses, it is mainly transmitted by sucking flies such as horse and deer flies. The virus survives in the fly and the disease infects other horses as the fly moves from one to the next. A herd can become infected in this manner quite quickly. Once they become infected, they are infected for life. There is no vaccine. There is no cure.

Once a horse becomes infected, they can enter one of 3 stages of disease. The first stage is the acute stage. This is a sudden onset of the disease with symptoms such as high fever, anemia (breakdown of red blood cells), swelling of the limbs, weakness, and even unexpected death. The subacute stage is less severe, but with similar symptoms. The disease will tend to progress at a slower rate than the acute phase and will often enter the chronic phase. The chronic phase is also known as a carrier phase. The horse may seem fine, but still carries the virus. He may tire easily and may have a recurrent fever and anemia. Relapses into the acute or subacute phases can occur years after the original attack. Most horses that test positive for EIA are not showing outward signs.

These are the reasons that we test for EIA. If an infected horse were to travel to a horse show, you can imagine what could happen. And it has happened. In 1947, there was an epidemic at a racetrack in New Hampshire where 77 horses either died or were euthanized after contracting the virus. But what exactly is the “Coggins test”?

The Coggins test is named after Dr. Leroy Coggins. He developed the lab test to diagnoses EIA at Cornell University in 1970. The procedure does not detect the virus, but it detects antibodies to virus. An antibody is a protein built by the immune system to attack foreign substances, known as antigens. The immune system only develops antibodies if an antigen is presented to it. In other words, if the horse has never been exposed to EIA, then it will not have antibodies against it.

The test that Coggins developed is called an Agar Gel Immunodiffusion test. What this means is that the serum (blood sample) is placed into a hole in a petri dish. If antibody (Ab) is present in the blood sample, as it diffuses out of the hole and into the agar gel, it will bind with the antigen (Ag) and form a precipitate. This is a positive test. If there is no antibody, then there is no precipitation, or the animal is negative. (See diagram below). This test takes about 2 days to complete. The USDA made it the official EIA test in 1973.

AGID Example

Example of AGID. (Ag = Antigen, Ab = Antibody, White line = Precipitate)
Occasionally we are asked to perform a STAT coggins, as it is needed right away. Another test that can look for antibodies is an ELISA (Enzyme Linked Immunosorbent Assay). Don’t worry too much about the jargon. This difference is that this is a quick and dirty test that only takes a few minutes to show if antibody is present. So why don’t we use this one? Well, it’s not as accurate and while it gives a quick answer, the AGID is still run to confirm it.
Blood Draw

If a horse is found to be positive for Equine Infectious Anemia, it poses a risk to any horses around it. Since there is no treatment, most horses are euthanized to prevent the spread of the disease. However, they don’t necessarily need to be put down. The horse can donated to a quarantined research facility, such as F.R.I.E.N.D.S. However very few of these exist and usually the horse would have to be moved, which isn’t legal without a negative coggins. They can also be quarantined on your own farm, where they must be kept at least 200 yards away from other horses. But this will be a lifelong quarantine.

Does every horse need a Coggins test? Actually, no. While it is recommended, if you maintain a small backyard herd that does not travel, the test may not be necessary. Keep in mind, though, that if one of them develops a fever and lethargy, they should be tested.

While we don’t see a lot of EIA anymore, it is still around. If you’re travelling with your horses, it’s important that you have an up to date Coggins certificate. Also, make sure that any horses that are coming onto your farm have been tested (and were negative!) for EIA. It may be difficult to eradicate this disease, but we can all help to prevent its spread.