Purdue News

April 21, 2005

Experts offer tips to protect animals and people

After the release of this article, the Centers for Disease Control and Prevention (CDC) announced approval of two more ingredients as effective and safe as mosquito repellents. The ingredients are picaridin and oil of lemon eucalyptus and join DEET as approved for protecting against mosquitoes. Further information is available online.

WEST LAFAYETTE, Ind. - Mosquito-transmitted illness can lead to paralysis and death or can be so mild that the infected person isn't even aware of the sickness.

Despite the potential seriousness of eastern and western equine encephalitis and West Nile virus, Purdue University experts say there are simple ways to protect yourself and your pets and horses.

"We advise that all horses in North America be vaccinated against eastern and western equine encephalitis and West Nile virus," said William Hope, Purdue equine community practice clinician.

Although the equine vaccines against these viruses are very reliable, no vaccine is 100 percent effective, Hope said. In addition, currently there are no human vaccines for these mosquito-borne illnesses. A vaccine based on the virus' DNA is in the U.S. Department of Agriculture approval process and eventually may lead to an inoculation that could be used for people.

Encephalitic diseases are spread when mosquitoes suck blood from infected birds and then bite people, horses or other mammals. Although a mosquito may bite an infected mammal, no evidence exists that the diseases can be spread from there 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, said Ralph Williams, a Purdue entomology professor.

Although eastern equine encephalitis, western equine encephalitis and West Nile virus have similar symptoms, their progression and fatality rates differ.

Eastern equine encephalitis can kill a horse in two to three days and is fatal in about 90 percent of cases. In humans, the disease's fatality rate is 35 percent to 50 percent. Western equine encephalitis is fatal in about 20 percent to 50 percent of equine cases and about 15 percent in human cases. West Nile virus kills 20 percent to 30 percent of horses struck, and about 3 percent of people. Western equine encephalitis and West Nile virus don't elicit any symptoms for one to three weeks after exposure.

Symptoms of the three diseases in horses include fever, lack of coordination, depression, loss of appetite and tremors. In severe and/or untreated cases, this can progress into paralysis and death. Even horses that survive often have temporary or permanent neurological problems sometimes severe enough that they can no longer be handled.

People should take precautions against mosquito-borne diseases, including:

• 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.

• Use repellents with N,N-diethyl-meta-toluamide (DEET) and follow label instructions.

• Make sure the repellent 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.

• Keep people and pets away from mosquito-infested areas. This is especially important at dawn and dusk, although some disease-carrying mosquitoes bite anytime.

According to the Centers for Disease Control and Prevention (CDC), DEET, which the U.S. Army developed in 1946, is available in 230 products registered with the Environmental Protection Agency. The CDC recommends using a mosquito repellent with DEET anytime you will be outside during insect season. The amount of DEET in the repellent determines how long it is effective. For instance, 23.8 percent DEET provides about five hours of protection, while 6.65 percent is good for about two hours.

Insect repellant should only be used on exposed skin or on clothing, but not on skin that is under clothing, according to the CDC. When using the repellent on a child, apply it to your own hands and then rub the repellant on the child, avoiding the eyes, mouth and cuts. Don't put repellant on children's hands because they often put their hands in their mouths.

It's safe to use an insect repellent along with a sunscreen, but the CDC recommends not using a sunscreen with repellent in it.

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
Agriculture News Page


Related Web sites:
Purdue School of Veterinary Medicine

Purdue Department of Entomology

Purdue Extension resources for West Nile virus

Animal and Plant Health Inspection Service

Centers for Disease Control and Prevention West Nile virus information


Related story:
Unpredictable weather, disease carriers make protection paramount


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