California encephalitis group
La Crosse virus is likely the most pathogenic member of the group, as most reported cases of infection by the California encephalitis group of viruses are by the La Crosse virus. La Crosse virus is transmitted via the Aedes triseriatus mosquito that is most active during the daytime. The eastern chipmunk, tree squirrel, and fox are mammalian hosts.
Human infections usually occur from late spring to early fall in the central and eastern United States. Patients who live near wooded areas or who participate in outdoor activities that may increase exposure to mosquitoes are at increased risk for this infection.
The incubation period is 5-15 days. Typically, infections are asymptomatic. Symptomatic infections present with headache, fever, and vomiting. Hyponatremia may be seen. Other less common symptoms include seizures, encephalitis, and focal neurological abnormalities. Neuroinvasive disease is uncommon (usually 100 or fewer cases are reported in the United States yearly). Most neuroinvasive cases occur in children.
A83.5 – California encephalitis
243617008 – Bunyavirus serogroup California
Differential Diagnosis & Pitfalls
- Other causes of viral encephalitis including herpes simplex virus, enterovirus, adenovirus, varicella zoster virus, West Nile virus, influenza, Eastern equine encephalitis, St. Louis encephalitis, rabies virus, and Japanese encephalitis virus
- Bacterial or viral meningitis
- Brain abscess
- Prion disease (eg, Creutzfeldt-Jakob disease)
- Autoimmune encephalitis
- Toxic ingestion (including alcohol or illicit drugs)