The virus (EIAV) is endemic in the Americas, parts of Europe, the Middle and Far East, Russia, and South Africa.

Contaminated surgical equipment and recycled needles and syringes, and bits[2] can transmit the disease.

The risk of transmitting the disease is greatest when an infected horse is ill, as the blood levels of the virus are then highest.

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.

[citation needed] Chronic: The horse tires easily and is unsuitable for work.

The horse may have a recurrent fever and anemia, and may relapse to the subacute or acute form even several years after the original attack.

According to most veterinarians, horses diagnosed EIA positive usually do not show any sign of sickness or disease.

[3] The Pantaneiro breed, found in the Pantanal, is tolerant to EIA but infected horses have lower productivity than uninfected ones.

In addition, most horse shows and events require a negative Coggins test.