Diagnosis of Equine Infectious Anemia Virus

The first step in diagnosing EIAV is when the horse is presented with clinical signs. There are other diseases which show similar clinical signs for differential diagnoses (see clinical signs). To determine what the horse is infected with, the diagnostician will conduct many tests to eliminate possible differentials and to assure that the horse is infected with Equine Infectious Anemia Virus. Although a large number of diagnostic tests have been described in the past, it is safe to say that there is no single test available today which will prove without doubt that a horse is suffering from equine infectious anemia. (9)

Laboratory Tests (Serology).
Serum should be collected for the correct identification of antibodies toward the virus. If there are antibodies present in the serum, it means there is virus in the horse that the body is trying to fight. The serological tests that are most commonly used are the agar gel immunodiffusion (or colloquially known in the horse world as Coggins) test. (2). However, horses are usually seronegative for Coggins for 2-3 weeks after infection and may not develop antibodies until 60 days! So a more sensitive test would be used to detect antibodies earlier, an ELISA test. Though the advantages are rapidity, sensitivity and objectivity, the ELISA test may also give more false positives (8).

One of the most valuable tests in virology is the polymerase chain reaction (PCR). Not only will it identify the virus the horse, but is also very competent at identifying the virus in the other equids (mules, donkeys, etc). Because it is a retrovirus that uses reverse transcriptase for viral infection, the method of reverse transcriptase polymerase chain reaction assays (RT-PCR) can be very useful. This type of PCR can identify the viral infection not only in horses but also in foals born to infected mares.
 
Another interesting diagnostic is serum lipids found in cases of Equine Infectious Anemia. The normal range of serum lipids in the horse is 149394mg/100 ml. However,  in horsesw with EIAV this level may increase drastically up to 2550mg/100 ml. This increase in serum lipid is so dramatic it can often discernible to the naked eye. The cause of the increase in serum lipid is not yet known; it is possible the lipids arise after the red blood cells are destroyed from the virus or perhaps from the damage to the other cells in the body. (9)

Once a positive diagnosis is attained, the veterinarian should contact the Canadian Food Inspection Agency, as Equine Infectious Anemia Virus is a reportable disease. See control and prevention for more information.