California Virus Antibody

California encephalitis virus (CEV) is a member of bunyaviridae family that includes La Crosse virus, Jamestown Canyon virus, and Tahyna virus. The first three viruses cause disease in the United States and the fourth causes disease in Russia. CEV was first isolated in 1943 from mosquitoes in Kern County, California. Two years later, three human cases of encephalitis were attributed to CEV.

CEV causes encephalitis usually during the summer months, most often  in children less than 15 years of age. The 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. The acute illness begins with headache, fever, and vomiting and usually lasts up to 3 days. These symptoms are soon followed by lethargy and disorientation. The disease progresses with central nervous system signs and symptoms such as stiff neck, seizures, focal neurological signs, pathologic reflexes, asymmetrical flaccid paralysis, and coma. CNS symptoms typically last for approximately 1 week. Approximately 10% of children experience seizures. Approximately 2% of children develop paresis. The early convalescent period includes emotional lability, irritability, and occasional headache. These symptoms usually resolve in two to three months. 

Cerebrospinal fluid usually shows lymphocytosis. Protein may be elevated and glucose is within normal limits. 

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.

References

Reeves WC, Hammon WMcD:  California encephalitis virus, a newly described agent: III. Mosquito infection and transmission .  J Immun 69:511-514, 1952.

Johnson KP, Lepow ML, Johnson RT:  California encephalitis: I. Clinical and epidemiologic studies .  Neurology 18:250-254, 1968.

Hilty MD et al. California Encephalitis in Children, Amer J Dis Child, 1972; 124:530=533.