Key points
- La Crosse is caused by a virus spread through the bite of an infected mosquito.
- La Crosse virus circulates in the environment between tree hole breeding mosquitoes and small mammals (such as chipmunks and squirrels) in eastern and north central United States.
- Infected humans are considered "dead-end" hosts, meaning they do not spread the virus to uninfected mosquitoes that bite them.
Primary cause
La Crosse is caused by a virus that is found in eastern and north central areas of the United States.
About the virus
La Crosse virus is a California serogroup virus, in the genus Orthobunyavirus, family Peribunyaviridae. Other California serogroup viruses found in the United States include California encephalitis virus, Jamestown Canyon virus, snowshoe hare virus, and trivitattus virus.
Members of the family Peribunyaviridae have three segments of single-stranded RNA. The virus particles are spherical or oval, enveloped, and 90-100 nm in diameter.
How it spreads
La Crosse virus spreads to people and animals through the bites of infected mosquitoes.
People are considered "dead-end" hosts, meaning they do not spread the virus to uninfected mosquitoes that bite them.
The virus does not spread by coughing, sneezing, touching, or other contact with someone who is infected.
Prevent La Crosse
Transmission cycle
Mosquitoes become infected with La Crosse virus when they feed on small mammals, such as chipmunks and squirrels. The primary vector for La Crosse virus is Aedes triseriatus (the eastern treehole mosquito), found in deciduous forest habitats (forests with trees that lose their leaves each year).
Ae. triseriatus is an aggressive daytime-biting mosquito, especially in or near woods where they reside. Ae. triseriatus normally lays its eggs in standing water collected in tree holes, but it will also lay eggs in containers with standing water, particularly discarded tires. La Crosse virus is passed from the female mosquito to the eggs she lays. The virus can survive in dormant eggs through the winter and develop into infected, adult mosquitoes in the spring.
