La Crosse Viral Encephalitis Sets Sights on Western North Carolina

North Carolina public health officials this week announced the season’s first confirmed case of the mosquito-borne illness La Crosse viral encephalitis (LAC). The patient – a child from Macon County – is recovering. There are at least 14 other suspected cases awaiting test results in Buncombe County.

LAC is a mosquito-borne virus that was discovered in La Crosse, Wisconsin in 1963. Most cases occur in children, teens and the elderly. Many people infected with LACV have no apparent symptoms. In others, symptoms usually appear within a few days to a couple of weeks after a bite from an infected mosquito. Symptoms include fever, headache, nausea and vomiting. Convulsions, tremors and coma can also occur in more severe cases.

Aedes Triseriatus, that’s the Eastern Tree-Hole mosquito for the non-geeks among us, is the species believed to be the primary means by which humans are infected with LAC. It is possible that Asian Tiger mosquitoes can transmit the disease as well.

Biting a chipmunk or squirrel that is infected with the virus infects mosquitoes. However, people cannot get LAC from chipmunks or squirrels.

Tree-Hole mosquitoes are daytime biters and get their name because they often lay their eggs in water-filled tree holes. However, Tree-Hole mosquitoes also breed in containers that hold water such as buckets, tires, backyard toys, tarps etc.

“This case is an important reminder that we all need to take precautions to prevent mosquito bites,” State Epidemiologist Megan Davies said. “In addition to La Crosse, mosquitoes may carry other viruses such as those causing eastern equine encephalitis, West Nile virus infection and other diseases.”

While other mosquito-borne diseases like West Nile virus infection occur throughout the state, LAC is found mostly in western North Carolina; it is the state’s most common mosquito-borne disease. Most cases in North Carolina are recorded in late summer and early fall.

State officials recorded 21 LAC cases in 2010. The U.S. Centers for Disease Control and Prevention records about 70 cases each year. The disease is rarely fatal, but in 2009, a Swain County child died as a result of infection. An earlier fatality was recorded in Transylvania County in 2001.

The North Carolina Department of Health & Human Services offers these suggestions for protecting yourself against mosquito-borne illness:

Use repellent: When outdoors, use insect repellent containing DEET, picaridin, IR3535 or oil of lemon eucalyptus on exposed skin as well as on clothing (mosquitoes will bite through thin cloth). Remember always to follow the manufacturer’s recommendations. Permethrin is a repellent/insecticide that can be applied to clothing and will provide excellent protection through multiple washes. You can treat clothing yourself or purchase pre-treated clothing. For best protection it is still necessary to apply other repellent to exposed skin.

Wear protective clothing: Wear long sleeves, pants and socks when weather permits.

Avoid peak biting hours: Avoid outdoor activity or use protective measures when mosquitoes are active, typically from dawn until dusk.

Install and repair screens: Have secure, intact screens on windows and doors to keep mosquitoes out.

Eliminate breeding areas from your home and yard: Mosquitoes can lay eggs even in small amounts of standing water. Fill tree holes in/around your yard with soil and empty standing water from flower pots, buckets, barrels, children’s wading pools and tires. Drill holes in tire swings so water drains out. Change the water in pet dishes and replace the water in bird baths weekly.

There is no vaccine against La Crosse encephalitis virus (LACV), so reducing exposure to mosquito bites is the best defense against getting infected with LACV or other mosquito-borne viruses. For additional information regarding mosquitoes and ticks, visit the N.C. Public Health website. For more information on insect repellent use in children, see the Healthy Children website. For specific information on the use of DEET on children see the American Academy of Pediatrics.

^{Aedes Triseriatus image: CDC}