La Crosse Virus: What You Need to Know

La Crosse virus (LACV) is a mosquito-borne illness primarily found in the upper Midwest, Mid-Atlantic, and southeastern United States. This virus is spread mostly through the bite of the eastern treehole mosquito, Aedes triseriatus, and over the past 20+ years, more cases have been seen in Ohio compared to other regions of the United States.

La Crosse virus was first identified in 1960 during an outbreak of viral encephalitis in La Crosse, Wisconsin. The examination of the brain tissue of a 4-year-old following their death led to its discovery, aiding public health officials in understanding a previously unknown cause of pediatric encephalitis.

While most infections are mild, the LACV infection can result in serious neurological complications, especially in children younger than 16 years old. Understanding the virus's symptoms, transmission and prevention methods is vital for pediatricians, parents and caregivers.

How Is La Crosse Virus Spread?

The mosquitoes' role in the lifecycle of LACV is as transmitter of the disease. Mosquitos get the virus from infected small mammals, such as squirrels and chipmunks, and then transfer it to humans through a bite. It stops there: LACV is only acquired through the bite of an infected mosquito and is not spread from person-to-person or from animals directly to people. Because this infection is spread by the Aedes sp. mosquito, most cases are during the summer and fall months (May-October).

La Crosse Virus Symptoms

Most people infected with LACV don’t have symptoms, and therefore the number of true cases of LACV infection is likely underreported. However, some do develop symptoms that can include fever, headache, muscle pain, and nausea (similar to an influenza-like illness). Patients may also develop signs and symptoms of meningoencephalitis (neck stiffness, changes in normal brain function, seizure activity).

• Symptoms typically appear 5 to 15 days after the initial mosquito bite. Initial flu-like symptoms can quickly worsen in severe cases, with neurological symptoms developing within a few days. Some patients may experience seizures as the initial symptom.
• The long-term effects of severe LACV cases are being studied, including the risk of epilepsy and neurobehavioral issues.

Treatment Options

There is currently no specific antiviral medication for treatment of La Crosse virus infection. Current treatments focus on managing fever, seizures (if present), and other associated conditions as they appear.

Prevention and Protection

Public health officials and pediatricians play an important role in educating communities about the risks and providing information on simple, effective prevention strategies. The best way to prevent La Crosse virus infection is to avoid mosquito bites and take protective measures. Prevention begins with controlling the mosquito population by eliminating standing water around homes to reduce breeding sites.

Protective measures for families include:

• Using EPA-approved insect repellents and wearing protective clothing such as long-sleeved shirts and pants when outdoors, especially during dawn and dusk.
• Aedes sp. mosquitoes are daytime biting mosquitos (particularly at dawn and dusk). Reducing time spent in areas where mosquitoes are abundant (like densely wooded areas, overgrown grass, standing water) and taking precautions during outdoor play can significantly reduce the risk of mosquito bites.