California arbovirus (La Crosse) infections. II. Precipitin antibody tests for the diagnosis of California encephalitis.

Precipitin antibodies to California group arboviruses were studied by double agar gel immunodiffusion (ID) and counterimmunoelectrophoresis (CEP). Forty children with California encephalitis (CE), 12 patients with other forms of meningoencephalitis, and 120 residents of endemic CE areas were tested. Precipitin antibodies were detected only in the 40 patients with CE, whereas hemagglutination-inhibiting, neutralizing, and complement-fixing antibodies were also found in persons without a history of CE. Precipitin antibodies did not persist for more than a year, in contrast to the other three antibodies which may be detected for 2 or more years. Of the children with CE, 36% had precipitin antibodies in their acute sera by CEP and 44% by ID. Precipitin responses were subtype-specific, and the patients reacted most strongly with La Crosse virus. The results indicated that precipitin techniques would be useful for the early detection of CE in some patients and that the presence of precipitin antibodies in a patient with acute central nervous system infection is strongly suggestive of CE. In addition, precipitin tests can be used to distinguish the California subtype responsible for CE in a given area.