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Disease Profile

La Crosse encephalitis

Prevalence estimates on Rare Medical Network websites are calculated based on data available from numerous sources, including US and European government statistics, the NIH, Orphanet, and published epidemiologic studies. Rare disease population data is recognized to be highly variable, and based on a wide variety of source data and methodologies, so the prevalence data on this site should be assumed to be estimated and cannot be considered to be absolutely correct.


US Estimated

Europe Estimated

Age of onset





Autosomal dominant A pathogenic variant in only one gene copy in each cell is sufficient to cause an autosomal dominant disease.


Autosomal recessive Pathogenic variants in both copies of each gene of the chromosome are needed to cause an autosomal recessive disease and observe the mutant phenotype.


dominant X-linked dominant inheritance, sometimes referred to as X-linked dominance, is a mode of genetic inheritance by which a dominant gene is carried on the X chromosome.


recessive Pathogenic variants in both copies of a gene on the X chromosome cause an X-linked recessive disorder.


Mitochondrial or multigenic Mitochondrial genetic disorders can be caused by changes (mutations) in either the mitochondrial DNA or nuclear DNA that lead to dysfunction of the mitochondria and inadequate production of energy.


Multigenic or multifactor Inheritance involving many factors, of which at least one is genetic but none is of overwhelming importance, as in the causation of a disease by multiple genetic and environmental factors.


Not applicable


Other names (AKA)

Californian encephalitis


Nervous System Diseases; Viral infections


La Crosse (LAC) encephalitis is a mosquito-borne virus that was first described in La Crosse, Wisconsin in 1963. Since then, it has been reported in several Midwestern and Mid-Atlantic states.[1] The LAC virus is one of many mosquito-transmitted viruses that can cause an inflammation of the brain (encephalitis). About 80-100 cases of this condition are reported each year in the United States.[2] Most cases occur in children younger than age 16. While most people who become infected have no symptoms, those who do become ill may have fever, headache, vomiting and lethargy (tiredness). Severe cases develop encephalitis accompanied by seizures. Coma and paralysis occur in some cases.[1][2] There is no specific treatment for LAC encephalitis. Supportive therapy is provided to those who develop severe cases of the disease.[2]


Most people infected with LAC encephalitis do not have symptoms. Those that do become ill may initially have fever, headache, vomiting and lethargy (tiredness). Severe cases may develop encephalitis, an inflammation of the brain, which is often accompanied by seizures. Coma and paralysis may also occur. Most cases that develop symptoms occur in children under the age of 16[1][2] Symptoms, if present, typically develop 5 to 15 days after the bite of an infected mosquito. Most cases occur during the summer months.[2]


There is no specific treatment for LAC encephalitis. Severe cases are treated with supportive therapy which may include hospitalization, respiratory support, IV fluids and prevention of other infections.[2]

Learn more

These resources provide more information about this condition or associated symptoms. The in-depth resources contain medical and scientific language that may be hard to understand. You may want to review these resources with a medical professional.

Where to Start

  • You can obtain information on this topic from the Centers for Disease Control and Prevention (CDC). The CDC is recognized as the lead federal agency for developing and applying disease prevention and control, environmental health, and health promotion and education activities designed to improve the health of the people of the United States.

In-Depth Information

  • Medscape Reference provides information on this topic. You may need to register to view the medical textbook, but registration is free.
  • The Monarch Initiative brings together data about this condition from humans and other species to help physicians and biomedical researchers. Monarch’s tools are designed to make it easier to compare the signs and symptoms (phenotypes) of different diseases and discover common features. This initiative is a collaboration between several academic institutions across the world and is funded by the National Institutes of Health. Visit the website to explore the biology of this condition.
  • Orphanet is a European reference portal for information on rare diseases and orphan drugs. Access to this database is free of charge.
  • PubMed is a searchable database of medical literature and lists journal articles that discuss La Crosse encephalitis. Click on the link to view a sample search on this topic.


  1. La Crosse Encephalitis. Virginia Department of Health. March 29, 2013; https://www.vdh.virginia.gov/Epidemiology/DEE/Vectorborne/factsheets/lacrosse.htm. Accessed 9/11/2015.
  2. La Crosse Encephalitis. Centers for Disease Control and Prevention (CDC). October 16, 2009; https://www.cdc.gov/lac/gen/qa.html. Accessed 9/11/2015.

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