La Crosse encephalitis
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|La Crosse Virus|
|Group:||Group V ((-)ssRNA)|
|Species:||La Crosse Virus|
|La Crosse encephalitis|
|Classification and external resources|
La Crosse encephalitis virus (LACV) is one of a group of mosquito-transmitted viruses that can cause encephalitis, or inflammation of the brain. LAC encephalitis is rare; in the United States, about 80-100 LACV disease cases are reported each year.
Most cases of LAC encephalitis occur in children under 16 years of age. LAC virus is a zoonotic pathogen cycled between the daytime-biting treehole mosquito, Aedes triseriatus, and vertebrate amplifier hosts (chipmunks, tree squirrels) in deciduous forest habitats. The virus is maintained over the winter by transovarial transmission in mosquito eggs. If the female mosquito is infected, she may lay eggs that carry the virus, and the adults coming from those eggs may be able to transmit the virus to chipmunks and to humans.
Anyone bitten by a mosquito in an area where the virus is circulating can get infected with LACV. The risk is highest for people who live, work or recreate in woodland habitats, because of greater exposure to potentially infected mosquitoes.
La Crosse (LAC) encephalitis was discovered in La Crosse, Wisconsin in 1963. It occurs in the Appalachian and Midwestern regions of the United States. Recently there has been an increase of cases in the South East of the United States. An explanation to this may be that the mosquito Aedes albopictus is also an efficient vector of La Crosse virus. Aedes albopictus is a species that has entered the US and spread across the SE of the US and replaced Aedes aegypti in most areas (which is not an efficient vector of LAC).
Historically, most cases of LAC encephalitis occur in the upper Midwestern states (Minnesota, Wisconsin, Iowa, Illinois, Indiana, and Ohio). Recently, more cases are being reported from states in the mid-Atlantic (West Virginia, Virginia and North Carolina) and southeastern (Alabama and Mississippi) regions of the country. It has long been suspected that LAC encephalitis has a broader distribution and a higher incidence in the eastern United States, but is under-reported because the etiologic agent is often not specifically identified.
LAC encephalitis cases occur primarily from late spring through early fall, but in subtropical areas where the mosquito is found (e.g., the Gulf states), rare cases can occur in winter.
It takes 5 to 15 days after the bite of an infected mosquito to develop symptoms of LACV disease.
LAC encephalitis initially presents as a nonspecific summertime illness with fever, headache, nausea, vomiting and lethargy. Severe disease occurs most commonly in children under the age of 16 and is characterized by seizures, coma, paralysis, and a variety of neurological sequelae after recovery. Death from LAC encephalitis occurs in less than 1% of clinical cases. In many clinical settings, pediatric cases presenting with CNS involvement are routinely screened for herpes or enteroviral etiologies. Since there is no specific treatment for LAC encephalitis, physicians often do not request the tests required to specifically identify LAC virus, and the cases are reported as aseptic meningitis or viral encephalitis of unknown etiology.
||This section contains instructions, advice, or how-to content. (September 2012)|
How can people reduce the chance of getting infected with LACV? Prevent mosquito bites. There is no vaccine or preventive drug.
Use insect repellent containing DEET, picaridin, IR3535 or oil of lemon eucalyptus on exposed skin and/or clothing. The repellent/insecticide permethrin can be used on clothing to protect through several washes. Always follow the directions on the package.
Wear long sleeves and pants when weather permits. Have secure, intact screens on windows and doors to keep mosquitoes out.
Eliminate mosquito breeding sites by emptying standing water from flower pots, buckets, barrels, and other containers. Drill holes in tire swings so water drains out. Empty children’s wading pools and store on their side after use.
LACV can survive the winter in the mosquito eggs that will hatch into infected mosquitoes in the spring. Cleaning potential breeding sites such as old tires or tin cans can reduce the number of infected eggs developing into infected mosquitoes. As the Aedes triseriatus mosquito prefers treeholes for breeding sites, you can reduce mosquitoes by filling treeholes in/around your yard with soil.
No specific therapy is available at present for La Crosse encephalitis, and management is limited to alleviating the symptoms and balancing fluids and electrolyte levels. Intravenous ribavirin is effective against La Crosse encephalitis virus in the laboratory,and several studies in patients with severe, brain biopsy confirmed, La Crosse encephalitis are ongoing.
Related conditions 
- McJunkin, J. E.; de los Reyes, E. C.; Irazuzta, J. E.; Caceres, M. J.; Khan, R. R.; Minnich, L. L.; Fu, K. D.; Lovett, G. D.; Tsai, T.; Thompson, A. (March 2001). "La Crosse Encephalitis in Children" (pdf). The New England Journal of Medicine 344 (11): 801–807. doi:10.1056/NEJM200103153441103. PMID 11248155.
- Center for Disease Control and Prevention (CDC) (January 2009). "Possible Congenital Infection with La Crosse Encephalitis Virus -- West Virginia, 2006-2007". MMWR Morbidity and Mortality Weekly Report 58 (1): 4–7. PMID 19145220.
- The Encephalitis Society A comprehensive resource on Encephalitis and providing support and information to those affected and their families
- "La Crosse Encephalitis". CDC. Retrieved 2012-02-25.
- Directors of Health Promotion and Education Facts Sheet La Crosse Encephalitis
- Encephalitis Global Inc. Offering information and support to encephalitis survivors, caregivers and loved ones.