Ralph Williams, Faculty Member, States Mosquitoes May Be Early and Numerous Due to Floods

Purdue News
By Susan Steeves
June 12, 2008

WEST LAFAYETTE, Ind. - Hoosiers should be extra vigilant this year to avoid mosquito bites because itching and scratching season likely will begin early due to June's massive flooding, according to Purdue University experts.

The heavy rains that hit Indiana the first 10 days of June will leave numerous areas of standing water, the breeding ground for mosquitoes, said Ralph Williams, a public health entomologist in the Department of Entomology. Initially, this will result in an influx of nuisance mosquitoes that don't transmit disease to people, but can carry canine heartworm to dogs

"As floodwaters recede, pockets of water may linger where mosquitoes can lay their eggs," Williams said. "With the earlier chance for the mosquitoes to breed, it's especially important to take precautions that will help keep the mosquitoes from spreading a disease to you."

As the water stands longer and becomes stagnant, it will become a harbor for other mosquitoes, including the type that carries West Nile virus, which potentially can be fatal to humans and horses.

The high probability of an early emergence of the Culex mosquitoes that carry West Nile virus means horse owners should ensure their animals are vaccinated against the disease and other mosquito-borne encephalitic illnesses, said William Hope of the Purdue community equine clinic.

"It looks like it will be a big mosquito season, so horses will have more of a chance to contract these diseases," he said. "Horses should be vaccinated now, if they haven't been already, and then receive a second shot in the fall."

The vaccine is effective for horses, but no vaccine has been developed to protect people or other animals against West Nile virus and related diseases. Other animals, including dogs and cats, can be infected, but it's rare for them to develop the disease, according to the Centers for Disease Control and Prevention.

Culex mosquitoes usually are most active in Indiana from mid-August through the fall. However, the Indiana State Department of Health already this year has found the virus in some mosquitoes.

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.

Mosquitoes spread West Nile virus when they bite an infected bird and then bite a person, horse or some other mammal. 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.

Of the more than 3,000 known mosquito species, Indiana is home to more than 50. Their life cycle is seven to 10 days, and they all breed in standing water.

Williams and Hope 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.

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

Sources:   William 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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