La Crosse encephalitis (LAC) is a rare disease that a person contracts via a bite from a LAC-infected mosquito. This mosquito-borne virus was first described in La Crosse, Wisconsin, in 1963, contributing to its name. Encephalitis refers to inflammation of the brain tissue, which this virus causes. Although it is rare, the LAC virus does affect 80 to 100 people a year and comes with symptoms that range from mild to severe.
How Do People Get La Crosse Encephalitis?
LAC virus is caused by the bite of a mosquito, most often the "tree hole mosquito". The eastern tree hole mosquito, also known as Aedes triseriatus, typically lives in holes in hardwood trees. It also leaves its larva in artificial containers that contain plant life, as well as discarded tires, pools, ponds, and marshes. Tree hole mosquitoes that the LAC virus has infected can pass it on sexually (males) and to offspring via eggs (females).
Since these mosquitoes are located near residential areas across the United States, it is common for them to feed on humans, which transmits the virus. The LAC virus can also spread to a human by splashing the mucous membranes in the nose, eyes, or mouth, as well as through ingestion. Once a person has been infected, they cannot spread the virus through coughing, sneezing, or touching another person. Blood or tissue donations have not been found to spread the virus either.
Who Is at Risk?
The LAC virus has shown to primarily occur in Midwestern, mid-Atlantic, and southeastern states across the United States, with most cases happening from late spring through early fall. This period can be extended through winter for states that experience warmer weather that make it possible for mosquitoes to remain active. People who live in or visit woodland areas, work outside, or participate in outdoor activities in states where cases have been reported are at risk of contracting the LAC virus. Most reported cases have been in children under the age of 16.
Symptoms of LAC
La Crosse encephalitis has an incubation period of five to 15 days, which is when symptoms will present themselves in the affected person. Most infected people do not show any symptoms. However, those who do present mild symptoms may experience fever, headaches, nausea, vomiting, and fatigue. In the cases with more severe symptoms, encephalitis will occur. This symptom tends to occur in children under 16 years old and can be accompanied by seizures, as well as possible coma and paralysis.
How Is La Crosse Encephalitis Diagnosed?
The diagnosis of La Crosse encephalitis is based on blood or spinal fluid. Just as for other viruses, tests for LAC virus try to locate antibodies that the body makes to protect against it. These tests can take place at your primary care office, a hospital, or an urgent care facility.
Once a diagnosis has been made, your physician will provide you with symptom management, as well as resources and specialist referrals that can be used to make this process easier on the patient. These resources can include local support, mental health support, and research opportunities.
What Is the Treatment of LAC Virus?
There is currently no known treatment for LAC virus disease. However, mild symptoms can be managed using over-the-counter medication that targets pain and discomfort. For more severe cases, hospitalization, respiratory support, IV fluids, and infection prevention can be used to manage the severity of the symptoms.
How to Avoid Getting the LAC Virus
Although there are no known vaccines to prevent the LAC virus or medicines to treat it, there are ways to avoid bites from a mosquito that could have it. Some of the precautions that can be taken to prevent mosquito bites include:
- Use insect repellent that contains 20–30% DEET, 10–20% picaridin, 10–20% IR3535, or 30–40% oil of lemon eucalyptus.
- Apply permethrin, a pesticide that kills mosquitoes, to clothes and gear.
- Wear long-sleeved shirts and long pants when you are outside.
- Install screens on windows and doors to keep mosquitoes out of the house.
- Reduce water that may collect near your home:
- Fill tree holes that may collect water.
- Cover trash and recycle bins.
- Clean up leaves and yard debris.
- Keep gutters clean.
- Create a drainage area for tire swings.
- Replace water in birdbaths, fountains, and pet dishes.
The Takeaway
La Crosse encephalitis, also known as LAC virus, is a rare disease that is found in and carried by mosquitoes and transferred to humans through a bite, splashing of a mucous membrane, or ingestion. It occurs throughout the United States but is primarily found in woodland areas during the spring and fall. It is seen mostly in children under the age of 16, and although some people who contract it experience few to no symptoms, there are rare cases that experience more severe symptoms, such as encephalitis. There is no known vaccine or medical treatment that is used to protect against and treat La Crosse encephalitis; however, risk can be managed by taking actions that prevent mosquito bites.
If you have been bitten by a mosquito and suspect that you have contracted La Crosse encephalitis, it is important to monitor your symptoms and treat the mild ones using over-the-counter medication to provide relief for discomfort and pain. If symptoms begin to worsen, be sure to speak with your doctor. In the case of severe symptoms like encephalitis, coma, paralysis, or seizures, hospitalization can be used to manage the symptoms and prevent further disease.