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Correction to This Article
The article incorrectly referred to the area of Virginia where the disease has largely been concentrated, which includes the Tidewater region, as the southwestern part of the state. The disease has been found largely in the state's southeast, which includes Tidewater.

Rare Disease That Has Already Killed One Horse Worries Virginia Health Officials

On Beltane Farm in Middleburg, VA., Sandy Vine rides Henry, her show jumper.
On Beltane Farm in Middleburg, VA., Sandy Vine rides Henry, her show jumper. (Tracy A Woodward - The Washington Post)

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By Derek Kravitz
Washington Post Staff Writer
Sunday, September 6, 2009

Northern Virginia's first-ever confirmed case of a rare mosquito-borne disease that is fatal to most horses is spreading concern among health officials who worry that the virus is somehow moving beyond its normal stamping grounds.

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Eastern equine encephalitis, a noncontagious virus spread by mosquitoes, not unlike West Nile Virus, was diagnosed last month in a 28-year-old mare from Middleburg in eastern Loudoun County's vaunted horse country. The mare -- which had been riddled with health problems, including kidney disease -- was euthanized Aug. 6. Brain tissue samples sent to the National Veterinary Services Laboratories in Ames, Iowa, were examined, and three weeks later the lab confirmed the encephalitis diagnosis.

"Frankly, no one expected for the test to come back positive. This is a very unusual case, and a lot of us have been saying to ourselves, 'Gee, what does this mean?' " said Elaine Lidholm, a spokeswoman for the Virginia Department of Agriculture and Consumer Services. "We don't know if it's an isolated case or there's more out there in the environment."

What makes the case so unusual is that the horse had not traveled outside Loudoun County, its owners told state officials. The disease -- which more commonly goes by the name "triple E" -- largely has been concentrated in southwestern Virginia, especially the Tidewater region, where mosquitoes are plentiful.

"Up here, we certainly have mosquitoes, but not the same as the marshy areas," said Martin O. Furr, a professor of equine medicine at Virginia Tech's Marion duPont Scott Equine Medical Center in Leesburg. "I suspect it's a random outlier case. But I suppose it could be the tip of the iceberg ready to hit us."

Sandy Vine, a Middleburg horse trainer and show-jumping judge who owns three horses, said her animals receive annual encephalitis shots. Vine said the Loudoun case is worrisome, especially because most horse owners in the area have little knowledge of the disease and its symptoms. "You don't know if the horse was by itself or with others or if the owners traveled a lot," she said.

Virginia's agriculture department began tracking equine encephalitis cases in 2000. Since then, it has found 50 cases in horses, goats, emus and alpacas, none north of Madison, a small community between Culpeper and Shenandoah National Park, about 75 miles from Loudoun.

Although there are effective vaccines for the disease, there is no cure. And although many horse owners vaccinate their animals every six to 12 months, with recommended booster shots in the interim, others have forgone the $10 shots. In horses, the Eastern strain of the disease is 75 percent fatal, health officials say.

About 240 cases have been reported in humans in the United States since 1964, according to the federal Centers for Disease Control and Prevention, with fewer since 1984 because of the decreasing number of people living near marshland. Since 2003, there have been five human cases in Virginia. The fatality rate for humans is lower than that for horses, but those who survive the disease can be left with mild to severe brain damage. Transmission of the virus is most common in and around freshwater hardwood swamps in the Atlantic and Gulf Coast states.

The report of triple E so far from its home base caught many Loudoun veterinarians by surprise.

James Joyce, a veterinarian at Blue Ridge Veterinary Associates in Purcellville, said the case is "concerning because it's a reminder that it's now here." But Joyce cautioned that the disease is not contagious and is "very uncommon to this region."

William H. McCormick, a Middleburg veterinarian who has been practicing in Loudoun since 1974, said that he had never seen a case of triple E in Loudoun but that an older horse with a weakened immune system could be more prone to the virus. He added that the diagnosis, taken by itself, was no cause for concern.

"I've seen West Nile over the years, but never triple E. You certainly don't want to vaccinate horses for something they aren't going to get, but I would do it if they're traveling to Florida or the Eastern Shore," McCormick said.

Furr agreed, saying the horse, due to its age, could have become more susceptible to viruses because of cortisol-secreting tumors. "Still, in the years I've been here, this is the first case I've heard about," he said.


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