Bandalero Ranch Blog

Veterinarian Blast - What is Coggins and Why do we test?

By Bandalero Ranch
Sep 14, 2012

Every day we submit blood samples to our laboratories for horses that are obtaining health certificates in order to attend shows or sales.  What is a ‘Coggins’ test.  Why do we do it?

The test is looking for the reaction of the body to the virus that causes Equine Infectious Anemia,

The Coggins test is the named after the veterinarian, Dr Leroy Coggins, that created the special test that identifies the immune response, or antibodies to the Equine Infectious Anemia Virus (EIAV).

EIA affects all species of equine, horses, donkeys, mules, zebras and ponies.  The disease is distributed around the world. It was first described and identified in France in 1843.  In the US only about 20% of all horses are routinely tested.  Our prevalence is basically unknown. 



Our most recent national outbreak occurred in Arkansas last year affecting 40 horses from one facility.  The incidence is highest in those states with a larger population of horse flies and deerflies. 

Infection with the EIA Virus results in recurrent episodes of cyclic fevers, lethargy, ventral edema, unexplained weight loss, anemia, bruises on the gums and other mucosa, and occasionally death.  Most horses have an immune response which will gradually control the disease within a year, and then will no longer show any sign of the disease.  Unfortunately these horses will be carriers of the virus for life. 

Notice machete like mouth parts

They may appear normal, but serve as a reservoir of infection for uninfected horses through the bites of flies, or other biological vectors.

Diagnosis is based primarily on serological testing.  There is no treatment. The US prohibits interstate travel of infected animals, and has attempted to prevent the spread of the disease by requiring every horse that crosses any state line to be negative.  States are variable in their requirements.  Some states ask that the horse have a negative test within 12 months, others within 6 months.

There are essentially three stage of the disease process.  The acute phase begins approximately 4 weeks post exposure.  The chronic phase lasts approximately one year, and the carrier or persistent phase endures for the rest of the horse’s lifespan.

The symptoms are variable and depend on the stage of the disease.  Acutely, the horse has a high fever, lethargy, ventral edema, and bleeding from the nose.  The acute stage is usually less than a week, and frequently goes completely unnoticed.

The chronic part of the disease results in repeated bouts of the above symptoms, gradually reducing in severity. Weight loss may be observed as the horse struggles to maintain normal blood values. After one year, the horse will usually no longer have any symptoms at all.  Most horses appear completely normal.

EIA is caused by a virus that is very closely related to HIV.  The body may learn to adjust to it, but it never can completely clear it. The virus cannot affect people or any other animals other than members of the equine family. Any sort blood to blood transmission can pass the virus. 

Horse Fly

Biting flies, sexual intercourse, or reused needles  and surgical instruments can all pass the virus.

There is no specific treatment other than supportive for EIA.  Because EIA is a reportable disease in the United States, positive horses may only be isolated from all other horses, euthanized, or transported to a recognized research facility.  If the horse is not euthanized, they are branded on the jaw with a specific two digit state code followed by the letter A, then a second two digit number specifying that specific horse .

The virus is not long lived outside of the horse’s body, and the contamination area is considered to be 200 yards (assuming this is accounting for the distance of the fly’s flight path)

Preventive vaccines are not yet available, and it is because of our governmental strict surveillance that this disease has been controlled in our country.  Outbreaks can and do still occur.  Testing should occur as a normal yearly check up, and before admitting any new horse to any facility.  Horses should never be injected with previously used needles, and fly control should be rigorously applied.

Dr. B.K. Thwaits Questions? Comments?

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