Seroepidemiology of California and Bunyamwera serogroup bunyavirus infections in humans in California.

Several human populations in California were surveyed cross-sectionally and longitudinally for neutralizing antibodies to selected arthropod-borne bunyaviruses in the California and Bunyamwera serogroups. Overall, the prevalence of antibodies to California serogroup viruses was 6.4% in 702 individuals sampled during 1963-1988. Comparative antibody titers in individual sera indicated that 4.1% and 1.6% of these infections were caused by viruses similar or identical to Jamestown Canyon and California encephalitis, respectively. Evidence of prior infection with the Jamestown Canyon serotype was found in 10% of 118 humans employed outdoors in high elevation areas and sampled in 1988, including 5 of 16 persons (31%) employed as rangers patrolling in remote forests and meadows. This probably reflects increased exposure to bites of boreal mosquitoes that breed in pools of melted snow. Antibodies to Bunyamwera serogroup viruses, including the Northway serotype, which was recently shown to be enzootic in California, were found in only 2 of 702 humans studied. No seroconversions were detected to selected California or Bunyamwera serogroup viruses in paired samples from 392 humans, including 349 patients with acute central nervous system disease or undifferentiated febrile illnesses who were sampled during 1963-1988, and thus these viruses are currently unconfirmed as human pathogens in California.