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California Virus Antibody

California (La Crosse) virus is a member of bunyaviridae that causes meningoencephalitis, usually in children less than 15 years of age.  Virus is transmitted to humans by various Aedes and Culex mosquitoes. Intermediate hosts include rabbits, squirrels, chipmunks, and field mice.

The incubation period is estimated to be 7 days and acute illness usually lasts for less than 10 days. The earliest symptoms are nonspecific and last up to 3 days. Central nervous system signs and symptoms such as stiff neck, lethargy, and seizures then appear and last for approximately 1 week. Approximately 10% of children have seizures and develop epilepsy. Approximately 2% of children develop paresis.

Diagnosis can be confirmed by testing for IgG and IgM antibodies in serum and cerebrospinal fluid. IgM and IgG antibodies can be detected in serum within 1 to 3 weeks after onset of symptoms. Antibody titers peak after 2 months and then begin declining. A positive IgG result indicates exposure to California virus, while a positive IgM result indicates acute infection. Specimens collected in the first two weeks of illness are often negative and should not be used to rule out infection.

A positive result for CSF IgG and/or IgM indicates intrathecal synthesis of antibody and is indicative of neurological infection. Contamination of CSF with blood may produce false positive results.

Antibodies are detected by incubating dilutions of cerebrospinal fluid (CSF) with substrate cells infected with virus. If antibodies to this virus are present in the serum or CSF of a patient, an antigen-antibody complex develops that can be detected by a fluorescein-labeled anti-IgG or IgM antibody.

Specimen requirement is at least 0.2 mL of serum or cerebrospinal fluid. Reference values are IgG: <1:10 and IgM: <1:10 for patients of all ages.

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