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West Nile virus season can take a bite out of the fun

Ag Communication
By Susan A. Steeves
August 29, 2007

WEST LAFAYETTE, Ind. - Although many people think of mosquitoes as being the villain of summertime, the type of mosquito that spreads the potentially fatal West Nile virus is usually most active in Indiana from mid-August through October.

So far this year, only four human cases of the disease have been reported in Indiana and none in horses. But now is the time to take simple steps to protect you and your animals from the blood-sucking pests and the possibility of being infected, according to Purdue University experts.

"The recent heavy rains washed the mosquito breeding areas away, but with more hot, dry weather, we could see an increased emergence of the insects," said Purdue entomology professor Ralph Williams. "Though this is peak time for West Nile virus-carrying mosquitoes, people should be vigilant against being bitten from spring through fall because different mosquitoes carry different diseases."

Among diseases that mosquitoes spread are West Nile virus, malaria, yellow fever, dengue fever, and Eastern and Western encephalitis. West Nile virus, and occasionally Eastern and Western equine encephalitis, St. Louis encephalitis, and La Crosse fever, appear in Indiana. People and some other mammals can contract all of these diseases, but horses don't contract St. Louis encephalitis or La Crosse fever.

Last year five of the 80 Indiana residents who contracted West Nile virus died, according to the Centers for Disease Control and Prevention. In the United States, 4,269 human cases were reported during 2006, resulting in 177 deaths.

Mosquitoes spread West Nile virus when they bite an infected bird and then bite a person, horse or some other mammals. Although a mosquito may bite an infected mammal, no evidence exists that the diseases can be spread to another mammal, or directly between mammals. This is because, unlike birds, there is not a high enough concentration of the virus in other animals to allow for transmission, Williams said.

An effective West Nile virus vaccine exists for horses, but a successful vaccine still hasn't been developed for people. It's important that horse owners keep all their animals' vaccinations current, said Bill Hope, a Purdue community practice equine veterinarian.

The first year a horse receives the West Nile shot, there are two immunizations spaced three to six weeks apart, followed by a booster six months later, Hope said. After that, the vaccine should be given twice annually, approximately six months apart, with the first one given between February and April. Horses also should be vaccinated annually for Eastern and Western encephalitis.

"Our incidence of West Nile virus in Indiana horses has decreased dramatically since the first cases appeared in 2002," Hope said. "The main reason for the decline in cases is public awareness and horse owners ensuring that their animals have been vaccinated. It's important that people be reminded that they need to continue the equine shots, including giving their horses the second of their annual West Nile virus shots."

Williams and Hope also recommend that people and animals avoid mosquito-infested areas as much as possible, especially during dusk and dawn, which are prime biting times for the insects. People should use insect repellents containing DEET and picaradin, Williams said.

Insecticides are available to spray on horses and around horse areas.

In addition, the experts recommend these precautions:

* Dispose of, empty and/or clean livestock watering troughs, ditches, puddles, birdbaths, rain gutters, buckets, old tires, ponds and swimming pools so mosquitoes can't breed.

* Make sure the mosquito repellent you use is registered with the U.S. Environmental Protection Agency and check that the concentration is approved for use on children.

* Don't use human anti-insect products on animals; those repellents could sicken an animal. Special repellents are available for horses, but not for dogs and cats.

* Wear light-colored clothing, long-sleeve shirts, long pants, socks and hats when outside.

* Cover horses with light-colored, lightweight or netted sheets to help keep insects away.


For more information about West Nile virus, visit www.entm.purdue.edu/publichealth


Writer: Susan A. Steeves, (765) 496-7481, ssteeves@purdue.edu

Sources: Bill Hope, (765) 494-8548, hopew@purdue.edu

Ralph Williams, (765) 494-4560, rew@purdue.edu

Ag Communications: (765) 494-2722;
Beth Forbes, forbes@purdue.edu
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