Arboviruses are defined as viruses that are maintained in nature and are transmitted between susceptible vertebrate hosts by blood-feeding arthropods such as mosquitoes.  The Microbiology Section no longer performs this testing in-house.

All About Arboviruses

St. Louis Encephalitis

What is St. Louis encephalitis?
Encephalitis means “inflammation of the brain.” St. Louis encephalitis (SLE) is caused by a virus and it spreads to people through the bite of infected mosquitoes. SLE causes disease mostly in humans and birds.

What are the symptoms of St. Louis encephalitis?
Most people with SLE infection have no symptoms or only mild flu-like symptoms. However, some people may develop more severe symptoms including headache, high fever, neck stiffness, stupor, disorientation, coma, tremors, seizures, and/or paralysis. The overall death rate is 5 to 15 percent.

Who is most at risk for St. Louis encephalitis?
People who engage in outdoor work and recreational activities in areas that have identified active cases are at a higher risk of becoming infected. Persons over the age of 50 seem to be at the greatest risk for developing severe SLE when infected with the virus.

Is St. Louis encephalitis a problem in West Virginia?
West Virginia has not reported cases of SLE in recent years. SLE has been found in West Virginia in the past, mostly during the 1970’s.

How is St. Louis encephalitis spread?
SLE is transmitted to humans by the bite of an infected mosquito. You cannot get SLE from another person.


West Nile Virus

What is West Nile virus?
West Nile virus is a cause of encephalitis (inflammation of the brain). West Nile virus spreads through mosquito bites and can infect people, horses, and birds.

What are the symptoms of West Nile virus?
Most people who get West Nile virus infection never have any symptoms at all. Some people have mild symptoms, such as fever, headache, and body aches. These people recover without any treatment.

A few people with West Nile virus infection are sick enough to go to the hospital. These people have a more severe illness with fever, fatigue, confusion, headache, weakness, nausea, vomiting, muscle aches, stiff neck, abdominal pain, and other symptoms. Among people that develop a severe illness, 3%-15% people may die from the infection. However, less than 1% of people that become infected with West Nile virus develop a severe illness.

Who is most at risk for West Nile virus?
People over age 50 are most at risk. People who go outdoors in the summer without taking precautions against mosquitoes may also be at higher risk.

Is West Nile virus a problem in West Virginia?
Many counties in West Virginia have had birds test positive for West Nile virus. Mosquitoes positive for West Nile virus have also been found in a few counties in the state. West Virginia has reported 0 to 3 cases in people and 0 to 4 cases in horses each year since 2002.
How is West Nile virus spread?
West Nile virus spreads through mosquito bites. West Nile virus is not spread through casual contact with a person who has the virus, such as touching or kissing.

LaCrosse Encephalitis

What is La Crosse encephalitis?
Encephalitis means “inflammation of the brain.” La Crosse encephalitis is caused by a virus and it spreads through the bite of infected mosquitoes. La Crosse encephalitis can infect people, chipmunks, and squirrels.

What are the symptoms of La Crosse encephalitis?
Most people with La Crosse infection do not get sick. Some people may develop a mild illness with symptoms of headache, fever, nausea, vomiting, drowsiness, and confusion. In severe cases, people may have seizures or go into a coma. La Crosse is rarely fatal, but children may have headaches, seizures, or other problems after they get well.

Who is most at risk for La Crosse encephalitis?
Children under the age of 16 are most at risk, but disease can occur at any age. Children are more likely to get the infection if:
  • They live near the woods;
  • There are cans, bottles, tires, or other containers that hold water lying around their house or play areas; or
  • They play outdoors frequently during June through October near areas were mosquitoes breed.

Is La Crosse encephalitis a problem in West Virginia?
In 2011, 27 cases of La Crosse encephalitis were reported in West Virginia. In the past, as many as 50 cases have been reported in West Virginia in a single year.
How is La Crosse encephalitis spread?
La Crosse encephalitis is spread by the treehole mosquito (Oc. triseriatus), the Asian tiger mosquito (Ae. albopictus), and the Asian rockpool mosquito (Oc. Japonicus). These mosquitoes can live in the woods and lay eggs in treeholes or containers that hold water. Tires, cans, bottles, buckets, tire swings, toys, or any container that holds water can allow mosquitoes to breed near your home.

How can I protect myself, family and community from Arboviruses?

The peak hours of mosquito activity is from dusk to dawn in warm weather.
The best protection is to lower the risk of being bitten. You can do this by the following:

  • Use an insect repellent containing DEET
  • Wear long pants and long-sleeved shirts when outdoors
  • Avoid outdoor activities during peak times
  • Clean up around where you work and play outside
  • Change water in bird baths or other decorations
  • Remove ANY standing water
  • Remove ANY object that might collect water that will not drain
  • Check any catch basins that are in your yard

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