Subacute: A slower, less severe progression of the disease. Symptoms include recurrent fever, weight loss, an enlarged spleen (felt during a rectal examination), anemia, and swelling of the lower chest, abdominal wall, penile sheath, scrotum, and legs.
Chronic: Horse tires easily and is unsuitable for work. May have a recurrent fever and anemia, may relapse to the subacute or acute form even several years after the original attack.
There are currently no statistics available on mortality of EIA. No statistics are available of horses actually dying of acute forms. See also
A horse may also not appear to have any symptoms, yet still tests positive for EIA antibodies. This horse can still pass on the disease. According to most veterinarians, horses diagnosed EIA positive are usually not showing any sign of sickness or disease.
EIA may cause abortion in pregnant mares. This may occur at any time during the pregnancy if there is a relapse when the virus enters the blood. Most infected mares will abort, however some give birth to healthy foals. Foals are not necessarily infected.
Studies indicate that there are breeds with a tolerance to EIA.
Recent studies in Brazil on living wild horses have shown that about 30% of the horses are chronically infected with EIA yet seem to live a normal life.
Reuse of syringes and needles is a risk factor for transfer of the disease. Currently in the United States, all horses that test positive must be reported to federal authorities by the testing laboratory. Options for the horse include sending the horse to a recognized research facility, branding the horse and quarantining it at least 200 yards from other horses for the rest of its life, and euthanizing the horse. EIA-positive horses are infected for life. The horse industry and the veterinary industry strongly suggest that infected horses, even if they are not showing any clinical signs, are enough of a reason to enforce such stringent rules, although there are no conclusions of the effect of the disease on the horse industry.
The Coggins test (agar immunodiffusion) is a sensitive diagnostic test for equine infectious anemia developed by Dr. Leroy Coggins in the 1970s.
Currently, the USA does not have an eradication program due to the low rate of incidence, however many states require a negative Coggins test for interstate travel. In addition, most horse shows and events require a negative Coggins test. Most countries require a negative test result before allowing an imported horse into the country.
It is recommended to verify that all the horses at a breeding farm and or boarding facility have a negative Coggins test before using their services. A Coggins test should be done on an annual basis. Tests every 6 months are recommended if there is increased traveling.