Relationship of California group virus infection and mental retardation: seroepidemiological observations

A plaque reduction neutralisation test was utilised to determine the prevalence of antibodies to California group virus (LaCrosse subtype) among 612 moderately to profoundly retarded subjects resident in two Wisconsin state institutions. Neutralising antibodies were detected in the sera of fifty-one (8 per cent) of the subjects tested. Age and sex differences in antibody distribution were not significant. When sero-logical data correlated with clinical case history records, antibody was found in the sera of 13 per cent (24/188) of a group in which mental retardation (MR) was attributed to "presumed psychological causes" and in 8 per cent (12/158) of a group for which the aetiology of MR was "encephalopathy". In a group of 254 subjects with MR of unknown aetiology, none of the sixty subjects with cranial anomaly and only two of the ninety-five (2.1 per cent) subjects with Down's syndrome were positive for antibody to CEV, while thirteen of ninety-nine (13.1 per cent) subjects diagnosed as "other cerebral defects" had CEV antibody. In a majority of the subjects with CEV neutralising antibody, MR was attributed to perinatal influences.