May Marks the Beginning of West Nile Virus Season

May marks the beginning of West Nile Virus season in Tennessee, and the Department of Health will once again monitor test results from mosquito pools across the state. In 2006, Tennessee saw an increase in the number of human West Nile cases over the previous year and the most since 2003, when 26 cases were reported. There were 22 human cases confirmed in 2006, with one fatality. Tennessee had more human West Nile Virus cases in 2006 than any of the surrounding states except Mississippi. Mississippi has already confirmed two human cases of West Nile Virus this year.

“While numbers of West Nile Virus cases are hard to predict, with the rise in cases last year it is possible we could see a more severe season in Tennessee this year,” said State Medical Entomologist Abelardo Moncayo. “Our testing programs help warn people of areas in which mosquitoes have been found to carry the virus, so the public can take precautions to protect themselves.”

Officials with the Tennessee Department of Health State Laboratory will test both mosquitoes and birds for WNV, and will begin testing robins for the first time this year. Tennessee’s state lab will test only American robins, blue jays and American crows for WNV. These three species are chosen because they are common in Tennessee, are easily recognized by the pubic, have high mortality rates from WNV and have proven to be the most efficient species for WNV detection. Birds and mosquitoes are submitted for testing by county surveillance officials. WNV cannot spread directly from birds to people. However, dead birds should not be handled with bare hands. Anyone who finds a freshly dead robin, crow or blue jay is urged to contact the county health department.

Mosquitoes become infected with WNV by feeding on infected birds, and can then transmit the virus to humans through their bites. Most human WNV infections are either asymptomatic or mild. Symptoms may include fever, head and body aches, and usually last only a few days. However, 80 percent of people who become infected with WNV have no noticeable symptoms. The virus cannot be spread from one person to another.

WNV can occasionally cause an infection of the brain in humans. Severe infections, which occur in less than one percent of human cases, may cause meningitis or encephalitis and result in high fever, neck stiffness, stupor or disorientation. Severe cases may also cause muscle weakness or paralysis.

Mosquito populations in Tennessee are at their peak May through October. Human cases of West Nile Virus (WNV) usually occur beginning in July or August. There is no human vaccine for WNV; therefore, Tennesseans are urged to take preventive measures to avoid being bitten by infected mosquitoes.

• Most mosquitoes likely to transmit WNV bite at dusk and dawn, so avoid being outdoors at these times. If you must go outside during these times, wear long sleeves, long pants and socks to protect yourself.
• Eliminate standing water near your home, which can serve as a breeding ground for mosquitoes. Many containers, even those as small as a bottle cap, can hold enough water for mosquitoes to breed.
• Keep windows and doors closed or cover them with screens to prevent mosquitoes from entering your home.
• Use insect repellant containing either DEET, Picaridin or oil of lemon eucalyptus.

There are guidelines for using the suggested insect repellants. Neither DEET nor Picaridin should be used on infants younger than two months old. Oil of lemon eucalyptus should not be used on children younger than two years of age. DEET at 30 percent concentration is the maximum level recommended for children and infants over two months old. None of these products should be applied around the mouth or eyes at any age.

“Personal protection is the key to preventing mosquito bites and thus preventing the possibility of infection with West Nile Virus,” said Moncayo. “We encourage all Tennesseans to follow these simple guidelines to help protect themselves and their families.”

Horses can also be infected with West Nile Virus. Tennessee had 8 confirmed cases of West Nile in horses in 2006. Horse owners should be sure that their animals are current on their vaccinations for West Nile as well as for eastern equine encephalitis, which is also carried by mosquitoes.

For more information on West Nile Virus, visit the Tennessee Department of Health Web site at http://www2.state.tn.us/health/CEDS/WNV/wnvhome.asp.