Equine Infectious Anemia (Swamp Fever)
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Equine infectious anemia (EIA), also known as swamp fever, is a potentially fatal disease caused by a virus that can infect all types of equines, including horses, mules, zebras and donkeys. In most cases, the disease begins with an acute phase of illness, followed by chronic cyclical symptoms, which continue throughout the remainder of the horse's life. Some horses do not show any symptoms but can still be a source of infection for other animals. EIA occurs throughout Ontario and is an ongoing concern for horse owners in the province.
EIA is often spread from the blood of an infected horse to a susceptible horse by a vector such as an insect or an infected syringe, needle or piece of surgical equipment. It is also spread through infected blood products, during breeding from an infected stallion to the mare, and by crossing the placental barrier from a pregnant mare to its fetus.
The EIA virus is transmitted from one horse to another by bloodsucking horse flies, deer flies, stable flies, mosquitoes and possibly midges. When insects begin feeding on an infected horse and are interrupted in their feeding, they can transfer the virus during a subsequent feeding on a susceptible horse. Feedings must occur within 30 minutes. Horse fly feeding is frequently interrupted because the horse fly's large size and noisy flight attract attention and their cutting/slashing mouthparts inflict considerable pain, causing the horse to move and the fly to switch to another horse.
The virus can cross the placental barrier and cause fetal infection. Mares with acute EIA symptoms during pregnancy run the greatest risk of infecting the fetus. Infected fetuses are often aborted but when borne live they often die within 2 months.
Following the first exposure to the virus, the infected animal may experience fever and hemorrhaging for 7-30 days. During this time, approximately one-third of infected horses will die. Following the initial acute stage of illness, those that survive may appear to return to health and then go on to experience cyclical relapses that are less severe, every 2-3 weeks.
Chronic symptoms that may occur continually during the course of the disease include:
The onset of these signs is often associated with stresses such as hard work, hot weather, racing, pregnancy or use of steroid drugs.
On occasion, an apparently healthy horse may carry the virus but never exhibit any symptoms of the disease. This horse is referred to as a carrier animal and is a constant source of infection.
Tentative diagnosis of the disease may be made based on observation of signs and symptoms. However, confirmation by blood test (generally an ELISA, sometimes a Coggins test) is required, particularly in the case of carriers that do not exhibit any symptoms.
To date, there is neither known treatment nor a satisfactory vaccine for EIA, partly because the virus is able to change over time. The key to prevention is the identification and control of infected horses.
To reduce the risk of infection and spread of the disease:
Equine infectious anemia (EIA) has been diagnosed all over the world. However, the actual number of infected animals in any particular geographic area will depend on several factors:
Contact the Canadian Food Inspection Agency:
For more information:
Toll Free: 1-877-424-1300