Abstract
IN an editorial article in Public Health Reports of April 5 the writer remarks that though equine encephalomyelitis may have existed for very many years in the United States, attention has recently been focused on it by the epidemic in Massachusetts in 1938 when human cases of encephalitis also occurred. There was, however, no indication of human contact infection in these cases. In 1939 only 8,000 cases of equine encephalomyelitis were reported in the United States, or only about 4 per cent of the number (184,662) reported in 1938. The incidence was 1 · 1 per 1,000 animals (horses and mules) in the affected counties and a case fatality of 30 per cent. The highest incidence was reported from counties in the far-western and Pacific States, a north-east-south-west strip of the central States and three Atlantic States, New Jersey, North Carolina and Florida. As in previous years, more than 90 per cent of the cases occurred in the summer or early autumn, This seasonal prevalence favours the current view that the principal means of transmission is by blood-sucking insects, especially mosquitoes. The prophylactic value of vaccination with a vaccine of chick embryo tissue is shown by the fact that the incidence of encephalomyelitis in vaccinated horses and mules was 0·37 per 1,000 in the vaccinated as compared with 1·2 in the unvaccinated. Other factors in the reduction of the disease were the retarding of insect breeding and increased resistance owing to previous attacks among the animals.
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Equine Encephalomyelitis in U.S.A. Nature 146, 91 (1940). https://doi.org/10.1038/146091c0
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DOI: https://doi.org/10.1038/146091c0