Equine Infectious Anemia - Eradication From Ireland
Another presentation from the recent 2008 AAEP Convention, this one by Dr. Simon More, described the outbreak and successful eradication of equine infectious anemia (EIA) from Ireland in 2006. A review of the outbreak itself, its investigation and management was also published in the most recent issue of the Equine Veterinary Journal (2008; 40(7):702-711).
Equine infectious anemia (EIA) (aka "swamp fever") is a very important disease in horses, and can also affect donkeys and mules. This is the disease for which horses are given a Coggins test, which is required every six months for horses attending most shows and competitions, and for horses traveling internationally. EIA is caused by a retrovirus, more specifically a lentivirus. Other important viruses in this group include several immunodeficiency viruses such as HIV. When the EIA virus infects a cell, it actually permanently incorporates its genes into cell's DNA, so affected animals are infected for life. Horses go through repeated bouts of illness - the earliest episodes are usually the most severe. Horses that survive the acute phase become persistent, often inapparent carriers, and serve as a reservoir for the virus. The primary means of transmission is via transfer of blood from infected horses. This can occur through blood-feeding insects such as horse flies and deer flies, or through use of blood-contaminated equipment such as dirty needles, surgical instruments and dental equipment.
Signs of EIA during acute episodes include fever, depression, lack of appetite, decreased red blood cell count (anemia) and decreased platelet count (thrombocytopenia). Lack of platelets can lead to petechial hemorrhages (tiny dots of blood, often first noticed on the gums or inside of the lips). Episodes typically last 3-5 days, but weeks or even months may go by between episodes. Illness may also be precipitated by stressful events or treatment with immunosuppressive drugs. In some horses the episodes become more frequent, and signs of chronic EIA develop. In addition to anemia and thrombocytopenia, these horses (often called "swampers") become very thin and may develop edema over their lower abdomens. If the condition becomes very severe, a horse may have very pale or yellow mucous membranes (e.g. gums, around the eyes), and some may have nose bleeds or even neurological signs.
Prior to the outbreak of EIA in June 2006, Ireland was free of EIA, an advantageous status for the horses who lived there, as well as their owners. Between June and December, 38 horses became infected with EIA. It is believed that the outbreak started with four foals that were given hyperimmune plasma for prevention of Rhodococcus equi infection that had been illegally imported from Italy. It is likely that the plasma was contaminated with the EIA virus, but unfortunately by the time the outbreak was identified there was no remaining plasma that could be tested. Transmission of the virus was thought to have occured through mechanical transfer of blood during veterinary procedures and vector transmission via horse flies. Additionally, it was suspected that several mares may have been infected through close contact with foals. Ongoing surveillance in Ireland has not identified any additional cases in the last two years, so it is believed that the disease has been eradicated. Investigation and control of the outbreak took a lot of cooperation between many different organizations and individuals. The study of the epidemiology was also very important in controling the disease, as not all of the cases followed the book!
