Tennessee Prepares For West Nile Virus Season

First West Nile Virus Positive Mosquito Pool Reported

Nashville, May 8, 2006

One pool of mosquitoes has tested positive this year in Shelby County documenting the first West Nile virus (WNV) activity in Tennessee. Tennessee is the fourth state this year to have shown positive tests for the virus in mosquitoes, horses, birds, or sentinel animals. There has been one human case of WNV reported from Mississippi.

Mosquito season in Tennessee runs from approximately May through October. This year, Memphis began to conduct WNV surveillance in mosquitoes in April. Human cases of West Nile Virus usually occur starting in July or August. Last year, a case of St. Louis encephalitis (SLE) also was reported in Tennessee. SLE is caused by SLE virus and is transmitted by mosquitoes as well. The same precautions should be taken for SLE as for WNV.

“Most mosquitoes species likely to transmit West Nile and St. Louis encephalitis viruses bite at dusk and dawn,” said Dr. Abelardo Moncayo, state medical entomologist. “People encountering such mosquito problems should use insect repellents containing either DEET, Picaridin, or oil of lemon eucalyptus. These ingredients are very effective when used in accordance to the label’s instructions.”

There are guidelines for use of the recommended products. Neither DEET nor Picaridin should be used on infants younger than 2 months; oil of lemon eucalyptus should not be used in children younger than 2 years of age. No product should be placed around the mouth or eyes at any age. DEET at 30 percent is the maximum concentration recommended for children and infants over 2 months of age. Picaridin is found in repellents worldwide and was distributed in the U.S. for the first time last year. Oil of lemon eucalyptus can provide protection time similar to low concentrations of DEET.

“The best protection is still to use insect repellent and other personal protective measures, starting now and continuing through the end of mosquito season. Eliminating mosquito breeding grounds is important throughout the spring and summer,” said Dr. Moncayo. “There is still no vaccine or treatment for West Nile virus, so prevention is crucial.”

Last year, there were 2,949 West Nile Virus human cases and 116 deaths reported nationwide. The most severe West Nile Virus (WNV) activity was in the southwestern part of the United States. Where and to what degree WNV will occur in 2005 is difficult to predict. Tennessee had 18 human cases with one death and an additional seven equine cases with three deaths during 2005. There was evidence of the virus in most areas of the state.

“For most areas of Tennessee, the first evidence of WNV will be noted by the public by the discovery of recently deceased crows or blue jays, which are currently being tested by the Tennessee Department of Health,” said Dr. Moncayo. “Only crows or blue jays will be tested, and they must be fresh and kept cool after discovery. Since testing procedures will differ by county, we urge citizens to contact their local health department to find out if testing is still being offered and where to take the bird(s).”

West Nile virus is a mosquito-borne virus, which can occasionally cause an infection of the brain in humans. Mosquitoes become infected when they feed on infected birds and can then transmit West Nile virus to humans and horses through mosquito bites. Most human infections are either asymptomatic or mild. Symptoms may include fever, headache and body aches, usually lasting only a few days. In fact, 80 percent of people who become infected with the virus have no noticeable symptoms. Severe infections, which occur in less than 1 percent of infections, may cause meningitis or encephalitis and result in high fever, neck stiffness, stupor or disorientation. There also may be some degree of muscle weakness or paralysis. The virus cannot spread from person to person.

Horse owners can also take precautions to protect their animals.

“West Nile virus can affect horses and it is important that horse owners make sure their horses are current on their vaccinations for West Nile virus as well as for eastern equine encephalitis virus,” said Dr. John Dunn, public health veterinarian.

The Department of Health emphasizes the following recommendations to help the public lower their risk of mosquito-borne illness:

• Use a mosquito repellent that contains DEET, picardin or oil of lemon eucalyptus and follow the directions on the label.
• Limit outdoor activities at dusk and dawn to the extent possible, since this is the time of greatest mosquito activity, if outside at dawn or dusk, wear protective clothing such as long pants, long-sleeved shirts and socks.
• Empty any receptacles that can collect stagnant water around your home and provide mosquito breeding sites.
• Keep windows and doors closed or cover them with screens to prevent mosquitoes from entering the house.

In addition to mosquito-borne illnesses, Tennessee has tick-borne illnesses that are reported every summer. These include Rocky Mountain spotted fever (RMSF), ehrlichioisis and Southern-tick associated rash illness (STARI). Ticks should be removed with fine tweezers by steadily pulling the tick off the skin. Do not use petroleum jelly, matches or nail polish to try to remove ticks. Wear long pants and pull white socks over pants in order to prevent ticks from grabbing on as you pass them as they quest from grass and foliage. DEET as well as permethrin-based repellents can be applied to clothing following label directions.

For more information about West Nile Virus, visit the Department of Health’s Web site at http://www2.state.tn.us/health/FactSheets/wnv.htm.