[Featured Equine Hazard] Equine Infectious Anemia

Veterinary Logo Equine infectious anemia (EIA) is an infectious disease among equidae (e.g., horses, ponies, mules and donkeys) that gradually destroys their immune system. Commonly known as "Swamp Fever" as the as early clinical cases were mostly discovered in areas noted for plenty of water and insects, the EIA virus is similar to the AIDS virus of humans. For both of these lentiviruses, which are transmitted only between members of the same species, there are no vaccines or cures available. Once an animal is infected with the virus, it is infected for life, regardless of the severity of the symptoms.

The frequency of EIA in the world has been lowered significantly by control measures introduced in the mid-1970's. Though most horses succumb rapidly to EIA, a percentage of infected horses do appear to recover. In actual fact, they still harbor the virus, and symptoms of the disease may resurface during times of stress. It is because of these carriers that horses have to be tested regularly, for it ensures that horses in the same stable are not exposed to the virus.

Transmission

Equine Infectious Anemia (EIA) is transmitted from horse to horse by the exchange of certain bodily fluids, usually blood. One mode of transmission is through insect bites, especially those of horseflies. The virus can also be transmitted by mechanical means. Instruments like hoof knives, needles and syringes that were used and contaminated with blood from an infected animal are mechanical procedures of infecting a healthy equine. Blood transfusions have also been implicated in transmitting EIA.

During gestation, if the levels of virus in the mare's blood are high enough, the foal may be infected with the virus too. It has been estimated that 10 percent of foals delivered from infected mares are infected at birth and remain carriers of the virus throughout their lives.

Signs and Symptoms

Initial signs of EIA, which occur 1 to 3 weeks after primary infection, may include anemia, intermittent or continuous fever, severe weight loss (even though the animal continues to eat well), profuse sweating, rapid breathing and depression.

The initial signs of EIA fall rapidly into one of these four patterns:

1. Acute EIA
An equine suffering from this type of EIA rarely survives, and can die within 3 to 10 days after the virus enters the bloodstream. An "acute horse" may be difficult to diagnose because the symptoms are very general (fever, depression, and no appetite), and it will not test positive on the Coggins test for a month and a half. Unfortunately, approximately one-third of these infected horses die within a month.

2. Subacute EIA
An equine suffering from this type of EIA can be very sick, and its condition may later become chronic. A "subacute horse" exhibits no sign of the virus for a long time, but it eventually progress to a state of continuing weight loss, rough hair coat, and anemia. Relapses of increasing severity are common.

3. Chronic EIA
An equine suffering from this type of EIA may have occasional attacks and develop symptoms such as weight loss, weakness, anemia, and ventral edema (swollen belly and legs). These signs will later subside, but may never recur. However, it has been discovered that the symptoms commonly resurface during periods of stress, hot weather, pregnancy and during other diseases. The horse may linger for a year or more before it dies.

4. Asymptomatic EIA (Carrier)
An equine suffering from this type of EIA may appear to be healthy, but actually, it will carry the disease for its entire life and is able to transmit the virus. However, the horse may develop into an acute or chronic case after hard work, stress, or from other diseases. Most carriers will not show any recognizable signs, but will test positive on a Coggins test.

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