California Serogroup Viral Disease

California serogroup viral disease is an acute inflammatory viral infection that commonly affects the brain, spinal cord, and meninges. It is caused by a virus from a group of related viruses called the California serogroup viruses. The group includes the La Crosse, Jamestown Canyon, Morro Bay, and Tahyna viruses. California serogroup viral disease commonly occurs in children ages 6 months to 16 years, with a peak incidence from ages 4 to 10. Adults may contract the virus, but they typically remain asymptomatic; when symptoms occur, adults develop fever or aseptic meningitis. California serogroup viral disease affects males more than females, possibly because males participate more frequently in outdoor activities.

Causes

California serogroup viral disease is transmitted to humans through the bite of an infected mosquito. After the mosquito inoculates the skin, the virus replicates, causing primary viremia. Next the virus spreads to the liver, spleen, and lymph nodes. If replication is efficient, the virus may continue spreading to the central nervous system through the cerebral capillary endothelial cells or the choroid plexus, causing viral encephalitis or aseptic meningitis. Most cases occur in the midwestern states during late summer and early fall.

Complications

Most patients with California serogroup viral disease recover completely; however, nearly 20% develop recurrent seizures or behavior problems. The associated mortality rate is less than 1%.

Assessment Findings

The incubation period for California serogroup viral disease is typically 3 to 7 days. Within 1 to 4 days, the child commonly develops abdominal pain, chills, fever, headache, nausea, photophobia, and vomiting. As encephalitis develops, the child may experience lethargy, somnolence, incoordination, focal motor abnormalities, and seizures. Nearly 10% of children progress to a coma state. The duration of illness is typically 10 to 14 days. Adults are commonly asymptomatic, have a benign febrile illness, or develop aseptic meningitis. If aseptic meningitis develops, signs and symptoms include fever, headache, photophobia, and neck stiffness.

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