Texas Sees Its First Case of West Nile Virus in a Horse

Preliminary tests on a sick horse that was euthanized Saturday, June 29, near Katy in far west Harris County, indicate that the animal was infected with West Nile Virus (WNV), a form of "sleeping sickness" first detected in Texas in two dead blue jays June 18 on the northwest side of Houston. According to the Texas Department of Health (TDH), another 29 infected birds have since been found.

"We were notified today (July 3) that tests run on samples of the horses's blood and spinal fluid were positive for WNV. The tests were run both at the Texas Veterinary Medical Diagnostic Laboratory (TVMDL) in College Station, and at the National Veterinary Services Laboratory (NVSL) in Ames, Iowa," said Dr. Linda Logan, Texas' state veterinarian and executive director for the Texas Animal Health Commission (TAHC), the state's livestock health regulatory agency.

"The NVSL is running additional confirmation tests on the blood samples, but more than likely, we are seeing Texas' first case of West Nile Virus in a horse. Diagnosing WNV must be based on laboratory confirmation, as the signs of the disease, including staggering or the inability to rise, can mimic other diseases, including rabies, or other encepalitic diseases, such as Western Equine Encephalitis (WEE) and Eastern Equine Encephalitis (EEE)."

WNV was unheard of in North America until l999, when it was detected in birds in New York. The virus, which can cause brain swelling and severe illness in horses, previously had been confined to Africa, Europe, Asia, and the Middle East. WNV has spread to 20 US states, following the migratory flight patterns of birds along the Eastern Seaboard and west as far as Texas. In 2001, 738 horses, donkeys or other members of the equine family were diagnosed with the disease in the U.S., and about 20 percent of the animals had to be euthanized, due to the severity of their illness.

"Blue jays, crows and more than 70 other species of birds can carry the virus, but it is the mosquito that puts the disease cycle in motion," explained Dr. Logan. "After feeding on infected birds, mosquitoes ingest the virus, and about one percent of the pests then become infected and capable of spreading the virus to horses or humans. There have been no documented cases of animals or humans spreading the disease. Dogs and cats appear to be resistant to the disease."

"Home and stable owners should take precautions to prevent mosquito bites," said Dr. Joe Garrett, a veterinarian with the TDH's Zoonosis Control Division. "Get rid of stagnant water, drain flowerpots, keep bird baths clean and cut weeds down to discourage mosquito breeding grounds. Apply insect repellents, and put up screens to protect your home or stable from being 'invaded' by mosquitoes. There is no vaccine for people, but fortunately, human cases of WNV are extremely rare. However, see your physician immediately if you develop signs of the disease, which include fever, headache, body aches and swollen lymph glands. More severe infection may be marked by headache, high fever, neck stiffness."

"We continue to work with other agencies to urge horse owners to have their animals vaccinated against WNV, and with the diagnosis of this disease in the Houston area, all possible preventive efforts are import to stop the spread of this disease," said Dr. Richard Ferris, area-veterinarian-in-charge for the U.S. Department of Agriculture's Veterinary Services in Texas. "We are investigating other potential cases in horses in Harris County and are awaiting test results. If you live in the Houston area, protect your horses from mosquitoes. While a vaccine is available for horses, the animal must receive two doses of WNV vaccine three to six weeks apart, and full protection does not begin until at least four to six weeks after the second dose of vaccine is administered," he said. "I'd urge owners to take action now to get horses protected."

"If your horse becomes ill and goes off feed, sways, develops head tremors, muscle twitches or cannot rise, contact your veterinarian, so he or she can collect and send in samples to us for diagnostic testing," said Dr. Lelve Gayle, executive director of the TVMDL. Laboratory confirmation of cases is particularly important for tracking the movement of WNV within the state. Dr. Garrett said the TDH is continuing its WNV disease surveillance statewide, which includes testing mosquitoes, dead crows, blue jays, hawks and sampling zoo birds. Dead crows, blue jays or hawks can be submitted for laboratory examination, by calling the nearest regional Texas Department of Health office or the Texas Department of Health in Austin at 1-512-458-7255.

"If you are picking up a dead bird, wear gloves and wash your hands afterward," explained Dr. Garrett. "The bird could have had parasites of other illnesses, and it's always advisable to keep a barrier---like gloves--between you and the dead bird."

Dr. Logan reminded livestock owners that, as always, the TAHC operates a 24-hour hotline at 1-800-550-8242 for taking reports of unusual signs in livestock, including:

  1. staggering, falling, or inability to rise
  2. illness affecting a large percentage of animals
  3. sudden death loss
  4. blistering around an animal's lips, teats or hooves
  5. unusual ticks or maggots

Additional information about WNV can be accessed on the internet at: http://www.tdh.state.tx.us/zoonosis/diseases/arboviral/westnile/westnile.asp.

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