The Coggins test is a standard fixture in a routine annual equine wellness appointment. Veterinarians usually pull blood for this test when they perform spring vaccines but, some horse owners may not fully understand why.

Coggins testing is often mandatory if your horse travels for competition or lives at a boarding facility. Many veterinarians recommend that every horse gets an annual Coggins test.

This test is critical for controlling the spread of Equine Infectious Anemia (EIA), a contagious and incurable disease with potentially fatal outcomes. Positive results must be reported to local animal health authorities, and infected horses must be quarantined.

This article will review everything you need to know about the Coggins test for horses and controlling the spread of EIA. Keep reading to learn why this test is vital for protecting the health of every horse on your farm and the biosecurity of the equine industry.

Coggins Testing for Horses

Named after Dr. Leroy Coggins, who developed the test in 1970, the Coggins test is a simple, reliable, and inexpensive way to prevent the spread of infectious disease in horses. [1]

A Coggins test is a laboratory test used to detect the presence of antibodies for equine infectious anemia in blood from horses, donkeys, and mules. These antibodies are present after exposure to the virus that causes EIA. [2]

Veterinarians use this test to diagnose EIA and identify horses as carriers of this transmissible disease. While several tests can screen for EIA antibodies, the Coggins test is the most popular. [2]

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Equine Infectious Anemia

Equine infectious anemia is a bloodborne viral disease that only affects members of the Equidae family. There is no vaccine for EIA, and infected horses become lifelong carriers. EIA is found throughout the world and is a reportable animal disease in the U.S. and Canada. [3]

The virus belongs to the same family of viruses as human immunodeficiency virus (HIV), but EIA is not transmissible to humans.

Testing for EIA

The Coggins test refers to a specific laboratory diagnostic test that uses agar gel immunodiffusion assay (AGID) to detect antibodies in blood serum. Veterinarians can also test for EIA using a competitive enzyme-linked immunosorbent assay (C-ELISA). [4]

The C-ELISA test produces faster results than the Coggins test, but there is an increased incidence of false positives. Horses that get a positive result from an ELISA test need a Coggins test to confirm the findings. [4]

Reverse transcription polymerase chain reaction assays (RT-PCR) can help confirm the diagnosis when tests yield conflicting results. PCR assays are also helpful for detecting maternal antibodies in foals born to infected mothers. [5]

Performing a Coggins Test

To perform a Coggins test, equine veterinarians draw blood from your horse to send to an accredited lab for analysis. These labs conduct the test to detect EIA antibodies and provide a positive or negative test result finding to the veterinarians.

A negative result means that the antibody was not detected in the horse’s blood, while a positive result means that antibodies are present. Veterinarians share the results with horse owners in Coggins papers. [2]

Coggins Papers

Horse owners use Coggins papers as proof of negative test results. These results expire one year after the testing date, so annual testing is necessary.

Coggins papers include critical information about the horse’s owner, stable/environment, and veterinarian. The report will also contain information to verify the identity of your horse, such as his name, registration number, breed, age, sex, colour, microchip, pictures, and marking descriptions.

A negative Coggins should accompany your horse whenever he travels or moves barns to show that your horse isn’t an EIA carrier.

Positive Coggins Tests

What happens if your horse receives a positive result on a Coggins test? Fortunately, the chances of a positive result are very low due to widespread control measures to prevent the transmission of infectious anemia in horses.

Since the emergence of the Coggins test over four decades ago, EIA-positive cases have dropped from 4% in 1972 to 0.002% in 2012. [6]

If your horse has a positive Coggins test, veterinarians must report the positive result to the state animal health authority. The veterinarian will then place the affected horse under quarantine and repeat the Coggins test to rule out a false positive.

Horse owners must permanently quarantine or euthanize the horse if the second test confirms an EIA diagnosis. Even if infected horses don’t show clinical signs of the disease, they can still transmit the infection to others. [7]

Quarantine regulations for horses with EIA are very strict. They require horses to be housed 200 yards away from other horses and kept in a barn covered in mesh to keep out biting insects. [8]

Most horse owners choose to euthanize horses with equine infectious anemia to prevent the spread of this disease and avoid long-term suffering.

Clinical Signs

Clinical signs for EIA can vary significantly between horses. When horses are infected, the virus replicates rapidly in the horse’s bloodstream.

The horse’s body responds by destroying the infected red blood cells, leading to anemia and associated symptoms. [3] Anemia describes a condition in which the body does not have enough healthy red blood cells to transport oxygen to tissues.

EIA typically progresses through different phases of infection after an incubation period of 15-45 days. The initial acute episode lasts 1-3 days. [3]

Common symptoms associated with acute infection include:

  • Fever
  • Lethargy
  • Jaundice
  • Rapid breathing and heart rate
  • Limb swelling
  • Nose bleeds
  • Blood in feces

Severe anemia and sudden death can occur in some horses with EIA. But many horses survive the acute stage and become asymptomatic carriers, showing no clinical signs of the disease. [7]

However, chronic cases can lead to repeated suffering from flare-ups caused by stress. Clinical signs aren’t a reliable indicator of the disease, so annual Coggins testing is critical for screening. [3]


Positive horses without clinical signs are still a reservoir of infection for other horses.

EIA is transmitted between horses by biting flies. Tabanids, such as horse and deer flies, are the primary transmitters. [9]

Biting insects spread EIA by taking blood from an infected carrier and introducing the infected blood to a non-infected horse. It’s impossible to eliminate all blood-sucking insects around horses, so there’s always a risk of transmission near an infected horse.

EIA transmission can also occur through contaminated needles, natural breeding, and in-utero transmission. [9]


There is no known treatment or vaccine for EIA. The virus remains present in white blood cells after the initial infection, where it can become elevated during periods of stress and lead to a recurrence of clinical signs throughout life. [10]

EIA can be fatal. The overall health of the infected animal, as well as the strain and dose of the virus, influence clinical sign severity and morbidity rate. If horses survive the initial infection, they become lifelong carriers. [11]

Carriers can transmit the disease to other horses and may experience recurrent flare-ups that lead to prolonged suffering.


Without a cure or vaccine, regular testing is the only way to monitor and control equine infectious anemia. A negative Coggins test verifies that horses don’t have the antibody for EIA at the time of testing. But additional biosecurity measures can help limit the risk of transmission. [12]

Effective fly control strategies can reduce the likelihood of infection with diseases transmitted by biting insects. Owners should implement fly management practices to control fly populations on their farms and protect their horses from biting insects with insect repellent and fly gear. [12]

Bloodborne diseases are also transmissible through needles and other veterinary equipment. Always use a sterile needle when injecting your horse or puncturing a multidose medicine bottle. [13]

Regularly evaluate your horses for signs of illness. If you suspect your horse has an infectious disease, immediately contact your veterinarian and separate the horse from the herd to reduce the chances of transmission. [13]

Requiring a negative Coggins for horses entering and leaving the premises will limit the likelihood of contact with an infected horse.

Coggin Test Requirements

State authorities, facility owners, and horse show organizers often require proof of negative Coggins when transporting horses. However, horse owners should consider annual Coggins testing for all horses, even if they don’t plan on traveling.

Interstate Travel

Proof of a negative Coggins is mandatory for travel across state lines in most U.S. states. Some stat