LaCrosse Encephalitis

 

• LaCrosse encephalitis is a rare viral disease that is spread by infected mosquitoes. It usually affects children.
• LaCrosse encephalitis is one of several mosquito-borne virus diseases that can affect the central nervous system and cause severe complications.
• LaCrosse encephalitis is found mainly in the upper midwestern United States and in the Appalachian region.
• There is no specific treatment for LaCrosse encephalitis.
• Prevention centers on controlling mosquitoes and avoiding mosquito bites.

 

What is LaCrosse encephalitis?

LaCrosse encephalitis is a rare disease that is spread by infected mosquitoes. It gets its name from LaCrosse, Wisconsin, where the infection was first recognized in 1963. LaCrosse encephalitis is one of a group of mosquito-borne virus diseases that can affect the central nervous system and cause severe complications and even death. Other similar diseases are eastern equine encephalitis, western equine encephalitis, and St. Louis encephalitis.

 

What is the infectious agent that causes LaCrosse encephalitis?

LaCrosse encephalitis is caused by the LaCrosse encephalitis virus, an arbovirus. Arbovirus is short for arthropod-borne virus. Arboviruses are a large group of viruses that are spread by certain invertebrate animals (arthropods), most commonly blood-sucking insects. In the United States, arboviruses are spread mainly by infected mosquitoes.

 

Where is LaCrosse encephalitis found?

LaCrosse encephalitis is most common in the hardwood forest areas of the upper midwestern United States and in the Appalachian region (West Virginia, North Carolina, Tennessee, Virginia). Most recent cases are from West Virginia.

 

How do people get LaCrosse encephalitis?

The LaCrosse encephalitis virus has a complex life cycle involving chipmunks and squirrels and a specific type of woodland mosquito (Aedes triseriatus). This mosquito breeds in tree holes and manmade containers and bites during the day. People are not an important part of the life cycle of the virus. In rare cases, however, people who live in or visit an area where the virus lives can be infected by the bite of an infected mosquito. After infection, the virus invades the central nervous system, including the spinal cord and brain.

 

What are the signs and symptoms of LaCrosse encephalitis?

LaCrosse encephalitis is usually a mild illness, with fever, headache, nausea, vomiting, and tiredness. People with severe disease, usually children, can have seizures, coma, paralysis, and lasting brain damage.

 

How soon after exposure do symptoms appear?

It takes from 5 to 15 days after the bite of an infected mosquito to develop symptoms of LaCrosse encephalitis.

 

How is LaCrosse encephalitis diagnosed?

Diagnosis is based on tests of blood or spinal fluid.

 

Who is at risk for LaCrosse encephalitis?

Anyone can get LaCrosse encephalitis, but some people are at increased risk:

• Children
• People who live in or visit woodland habitats
• People who work outside or participate in outdoor recreational activities in areas where the disease is common

 

What is the treatment for LaCrosse encephalitis?

There is no specific treatment for LaCrosse encephalitis. Antibiotics are not effective against viruses, and no effective anti-viral drugs have been discovered. Care of patients centers on treatment of symptoms and complications.

 

What complications can result from LaCrosse encephalitis?

Some children have ongoing seizures and swelling of the brain, but deaths are rare.

 

How common is LaCrosse encephalitis?

During an average year, about 75 cases of LaCrosse encephalitis are reported. Most cases occur in children under age 16 years.

 

Is LaCrosse encephalitis an emerging infectious disease?

Yes. LaCrosse encephalitis virus was first isolated in the United States in 1963. The risk of exposures has been increasing as people move into previously undeveloped areas where the virus lives.

 

How can LaCrosse encephalitis be prevented?

There is no vaccine for LaCrosse encephalitis. Prevention centers on public health action to control mosquitoes and on individual action to avoid mosquito bites. To avoid being bitten by the mosquitoes that cause LaCrosse encephalitis:

• Eliminate breeding sites (tires, buckets, cans, etc.) near houses.
• When outside, wear long pants and long-sleeved shirts.
• Treat exposed skin with an insect repellent.

 

This fact sheet is for information only and is not meant to be used for self-diagnosis or as a substitute for consultation with a health-care provider. If you have any questions about the disease described above, consult a health-care provider.