Skip to Content
Agencies | Governor
Search Virginia.Gov
Protecting You and Your Environment Virginia Department of Health
Home | VDH Programs | Find It! A-Z Index | Newsroom | Administration | Jobs
   disclaimer

La Crosse Encephalitis


 pdf Version | Information from CDC about La Crosse Encephalitis

What is La Crosse encephalitis?

La Crosse (LAC) encephalitis is a mosquito-borne virus that was discovered in La Crosse, Wisconsin in 1963. Since then, the virus has been identified in several Midwestern and Mid-Atlantic states, including western parts of Virginia.

Who gets LAC?

Most cases of LAC encephalitis occur in children under 16 years of age.

How is LAC transmitted?

LAC is transmitted to humans through the bite of an infected tree-hole mosquito. Mosquitoes are infected by biting a chipmunk or squirrel that is infected with the virus. The virus may be spread by infected mosquitoes to their eggs. Tree-hole mosquitoes are daytime biters and can live not only in tree holes, but also in containers that hold water including buckets, tires, backyard toys, tarps etc.  Asian tiger mosquitoes are potential vectors of LAC. People can not get LAC from chipmunks or squirrels.

What are the symptoms of LAC?

LAC is typically a summertime illness. Initial symptoms include fever, headache, nausea, vomiting and lethargy. Severe disease occurs most commonly in children under the age of 16, often 6-9 year olds, and is characterized by seizures, coma, paralysis, and a variety of neurological complications after recovery. Death from LAC encephalitis occurs in less than 1% of clinical cases, but children with severe disease may suffer from learning disabilities and other neurological deficits.

How many human cases of LAC have been reported in Virginia?

The first human case of LAC was reported in the state in 1996.  Generally between 0 and 4 cases of LAC are reported in Virginia each year. There was one case of LAC in Virginia in 2009.

How Can LAC be prevented?

  1. Wear long, loose and light-colored clothing.
  2. If possible, stay indoors when mosquitoes are biting.
  3. Use insect repellant with the smallest percentage of DEET necessary for the length of time you are exposed to mosquitoes, follow manufacturer’s directions when using repellants
  4. Turn over or remove containers in your yard where water collects, such as old tires, potted plant trays, buckets and toys. 
  5. Eliminate standing water on tarps or flat roofs.
  6. Clean out birdbaths and wading pools once a week. 
  7. Clean roof gutters and downspout screens.

Where can I get more information on LAC?

Call your local health department of visit one of the following sites:


Last Updated: 03-29-2013

Printable Version

E-mail This Page