Human Equine Encephalomyelitis and St. Louis Encephalitis in California, 1939-1941

Abstract

A comprehensive study of encephalitis in California, based largely on serum-neutralization tests, is presented for the years 1939, 1940 and 1941. The epidemiological, clinical and laboratory evidence indicates that the virus of western equine encephalomyelitis has become endemic in the central valleys of California for man and animals and that the St. Louis strain is likewise closely associated. From the finding of antibodies in the sera of fowl and mammals in endemic areas and in children under 1 yr. of age, it is apparent that the St. Louis virus has been in California for some time and is not imported from the midwestern States, as formerly proposed.