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August 26, 1944


JAMA. 1944;125(17):1192-1193. doi:10.1001/jama.1944.02850350030013

Since the St. Louis epidemic of 1933, many clinicians have assumed that epidemics of acute encephalitis are due to person-to-person droplet infection. The causative agent of the disease, however, has never been isolated from nasopharyngeal washings, and the seasonal variations and topographic distribution strongly suggest an insect vector. Following Syverton's1 experimental transmission of western type equine encephalomyelitis by means of the wood tick, and the implication of several species of ticks by Soviet investigators,2 Blattner and Heys3 of the Department of Pediatrics, Washington University School of Medicine, began a study of the relation of the St. Louis encephalitis virus to the common dog tick (Dermacentor variabilis).

The dog tick is relatively common in the environs of St. Louis and is readily reared under laboratory conditions. Adult females feeding on guinea pigs or hamsters require on an average four to six days for complete engorgement. Four days later

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