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Texas Agriculture Archive

July 5, 2002

West Nile virus
discovered in Houston

Veterinarians with the Texas Animal Health Commission are urging horse owners to ensure their animals are vaccinated for West Nile Virus (WNV), a form of "sleeping sickness," which was confirmed June 18 in two dead blue jays found on the west side of Houston. They are also urging equid owners to vaccinate their animals for Eastern and Western Encephalitis, two other common forms of "sleeping sickness."

"The introduction of West Nile Virus into Texas isn't surprising, as we have monitored the south and eastward migration of the disease since it was first detected in North America in New York in l999. Last year, WNV was reported in 738 equids in 20 states," commented Dr. Terry Conger, TAHC's state veterinary epidemiologist.

The disease, which can be transmitted from infected mosquitoes to humans and equids, causes brain swelling and severe illness.

Dr. Conger said that the cycle of disease for WNV requires two key players: birds, such as crows, blue jays or hawks, that act as a reservoir for the virus, and mosquitoes that become capable of transmitting disease after they take a blood meal from an infected bird. According to the Centers for Disease Control (CDC) in Atlanta, GA, there have been no documented cases of person-to-person, animal-to-person or animal-to-animal transmission of WNV.

"Late last summer, infected birds were detected in Louisiana and Arkansas," said Dr. Conger. "Now with the confirmation of infected birds in our state, the Texas Department of Health will probably find infected mosquitoes through their surveil-lance activities."

Although vaccines are available to protect equids from WNV and other sleeping sicknesses, the shots must be given before disease exposure.

"We are running out of time before we may see disease transmission, so get your equids vaccinated now," Dr. Conger urged. "The vaccines require two doses, administered three to six weeks apart, and full protection doesn't develop until four to six weeks after the second dose. Realistically, then, it can take seven to 12 weeks for the horse to develop maximum resistance to infection. That's why it's so important to start the round of vaccinations now."

Dr. Conger reminded equid owners that an annual booster is required for continued protection of the animals.

He said equid owners should call their veterinarian immediately if their animal has signs of illness such as staggering or an inability to rise.

"It is also extremely important to rule out other causes of sickness with similar signs, such as rabies," he said. "If it is WNV, appropriate care must be provided quickly. Historically, about 20 percent of infected equids either die or had to be euthanized due to their illness."

According to Kathy Barton, spokeswoman for the City of Houston's Health and Human Services Department, the threat of WNV to humans is relatively small—about the same as St. Louis encephalitis. She said about 1 percent of mosquitoes in an affected area carry the virus. Of the people who get bitten, only 1 percent become seriously ill.

Of those that become severely ill, a minority will develop more severe symptoms that include meningitis or encephalitis, and death can result.

Most people with WNV will show no symptoms. Those who do will typically develop mild symptoms such as fever, headache, body aches and skin rashes.

The Culex mosquito, which bites from dusk to dawn, is the primary carrier.

Monitoring for WNV by various mosquito control agencies, Texas A&M University and the Texas Department of Health has been intensified in Harris and surrounding counties in the upper Gulf Coast region. This includes testing mosquitos, sentinel chickens, dead crows, blue jays and hawks, zoo birds and horses.

State health officials are asking that large die-offs of birds be reported to the toll-free hotline, (800) 252-8239.

Dr. Jim Olson, entomologist with the Texas Agricultural Experiment Station, said Texans should practice personal precaution, premise clean-up and mosquito-proofing of homes to reduce the chance of the disease.

"The first thing people need to do is get rid of all the mosquito breeding sites they can find," he said. "Anything that is collecting and holding water for longer than three days needs to be either filled in, thrown away, turned upside down, or whatever."

To prevent mosquitoes from getting inside the home, make sure screens fit tight against windowsills and make sure there is weather-stripping around doors.

When going out doors, wear protective clothing and use a repellant.

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