Swamp fever cases in California a reminder of need for vigilance

Cross section of the 'equine infectious anemia virus.
A cross-section of the equine infectious anemia virus. USDA

The positive tests for equine infectious anemia (EIA) in more than 30 racing quarter horses in California should serve as a reminder that owners must follow regulations to keep the viral disease in check, an expert says.

Following regulations is critical, says Neely Walker, an equine specialist with Louisiana State University’s AgCenter. Louisiana state law requires that owners must test their horses for the disease annually.

EIA affects horses, mules, donkeys and zebras. It is also known as swamp fever because of its prevalence in the Gulf Coast region.

There is currently no effective treatment or vaccine. The survival rate is high, Walker said, but those animals can threaten the health of their offspring and other horses.

The virus is typically transmitted from one horse to another by blood-sucking insects, such as horseflies, deerflies, mosquitos and gnats. Many epidemics of EIA have also been linked to the reuse of hypodermic needles or nonsterile surgical equipment, Walker said.

EIA can present itself in three different degrees of infectiousness: acute, chronic and inapparent.

“Most horses are inapparent carriers of EIA and appear normal, displaying no clinical abnormalities associated with infection,” Walker said. “However, they are lifelong carriers of the virus.”

The acute form is the most damaging and is difficult to diagnose. This form often occurs seven to 30 days after the first exposure to the virus and may cause fever and bleeding on the mucus membranes, Walker said.

If a horse survives the acute stage, it may develop chronic symptoms such as fever, small patches of hemorrhages on the mucus membranes, depression, weight loss, anemia and swelling of the legs and abdomen.

Diagnosis of the virus was not possible until the 1970s, when Leroy Coggins developed a test, which became known as the Coggins test. Today’s tests can produce results in less than one hour.

“Accurate testing allows timely identification of infected animals and removal of those animals from herds, potentially preventing the spread of the disease,” Walker said.

Animals that test positive for EIA in Louisiana must be euthanized or sold for slaughter only. All animals located within 200 yards of an animal with EIA are subject to quarantine and require a negative test before a quarantine release will be issued.

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