La Crosse: Causes and How It Spreads

Key Points

  • La Crosse is caused by a virus transmitted through the bite of a mosquito.
  • La Crosse virus circulates in the environment between tree hole breeding mosquitoes and small mammals (e.g., chipmunks, squirrels) in eastern and north central United States.
Child scratching a mosquito bite

Primary cause

La Crosse is caused by a virus that is found in eastern and north central areas of the United States.

La Crosse virus belongs to a group of similar viruses, such as Jamestown Canyon virus or Snowshoe hare virus, which are also found in the United States and Canada.

How it spreads

  • La Crosse virus circulates in the environment between tree hole breeding mosquitoes and small mammals, such as chipmunks or squirrels.
  • Infected mosquitoes can then spread the virus to people and other animals by biting them.
  • People are considered "dead-end" hosts. This means they do not spread the virus to mosquitoes that bite them.
  • La Crosse virus is not spread by coughing, sneezing, touching, or other contact with someone who is infected.
Keep Reading: Transmission of La Crosse Virus
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Content Source:
National Center for Emerging and Zoonotic Infectious Diseases (NCEZID)