Human Equine Encephalomyelitis in Kern County, California, 1938, 1939, and 1940

Abstract

The western virus of equine encephalomyelitis is endemic among the human as well as the horse population of Kern County, Calif. Through analysis of serum neutralization tests, it is shown that for 1938, 1939 and 1940, respectively, of 112 encephalitic cases, the sera of 97 (86.6%) were positive for the virus of encephalomyelitis, and of 82 cases diagnosed as poliomyelitis, 5 (6%) were also positive for the equine virus. The sera of 6 of 82 (7.3%) well contacts and 29 of 41 (70.7%) sick contacts (mild cases) had neutralizing antibodies to the same virus. Cases of equine encephalomyelitis in all 3 yrs. predominated in the group under 10 yrs. of age, with a noticeable number under 1 yr. Males predominated over [female][female] among the encephalitic patients, as well as those having poliomyelitis. The western strain of the virus of equine encephalomyelitis was recovered from the brain of one infant and one adult in 1940. All cases developed in the farming and irrigated areas in the central and western portion of the county, beginning in May, increasing to a peak in July or Aug., then dropping off abruptly with only a few in Nov.