Key points
- La Crosse virus spreads to people through the bites of infected mosquitoes.
- Most people infected with the virus do not have symptoms.
- Some people may develop severe illness, most commonly children under 16 years old.
- You can reduce your risk of infection by preventing mosquito bites.
Overview
La Crosse is a disease caused by a virus spread infected mosquitoes. Most cases occur in the upper Midwestern, mid-Atlantic, and southeastern states.
Symptoms
Most people infected with the virus do not have symptoms. Initial symptoms can include fever, headache, nausea, vomiting, and fatigue. Some people may develop severe disease, including encephalitis (inflammation of the brain). Severe disease occurs most often in children under 16 years old.
How it spreads
La Crosse virus spreads to people through the bites of infected mosquitoes.
Prevention
No vaccines or medicines are available to prevent La Crosse. You can reduce your risk of infection by preventing mosquito bites.
Testing and diagnosis
See your healthcare provider if you have symptoms after being exposed to mosquitoes in an area where La Crosse virus spreads.
Treatment
No medicines are available to treat La Crosse. Antibiotics do not treat viruses. Rest, fluids, and over-the-counter pain medications may relieve some symptoms. Patients with severe disease often need to be hospitalized to receive support for breathing, staying hydrated, or reducing swelling in the brain.
Personal stories
Leah's story: How La Crosse encephalitis affected one family
When Leah was just 4 years old, she was bitten by a mosquito carrying La Crosse virus. Two days after complaining of a headache that would not go away, Leah’s family took her to the emergency room. Leah died in her parents’ arms three days later from La Crosse encephalitis.
Janeen’s story: Mosquitoes, ticks, and a weakened immune system
B cell-depleting therapy helped Janeen's father Steve enjoy his favorite pastimes—gardening and spending time with his family—while living with rheumatoid arthritis. The treatment also weakened his immune system and increased his risk of serious illness from viruses spread through mosquito and tick bites.
Sadly, Steve passed away shortly after being diagnosed with severe West Nile virus disease. His family shares his story and offers practical tips for protecting people with weakened immune systems.
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