Abstract
Through the studies of TenBroeck and Merrill 1 and Giltner and Shahan 2 it is known that the Eastern viruses of equine encephalitis isolated during the epidemic of 1933 are serologically distinct from those responsible for the disease in California, Nevada, Colorado, Utah and South Dakota. Rosenbusch 3 studied a similar if not identical malady in Argentine. He found the South American virus immunologically identical with the California virus. A comparative study of the 3 viruses, on horses, suggested itself. The senior author is familiar with the clinical and pathological findings observed in horses during the 1912 epidemic in Delaware and during the outbreaks in California (1930 to 1933), Colorado and Texas. The results of these studies may be summarized as follows:
(1) Two Eastern viruses (Delaware isolated from a brain sent to California in glycerine, New Jersey courteously furnished by Dr. Carl TenBroeck) infected horses when injected intracerebrally, intravenously (filtrates) and intracutaneously. In one series 1 cc. of a 20% suspension of guinea pig passage virus fatally infected 4 of 14 horses injected intracutaneously on the neck (distribution of cervical nerves). The clinical picture (fever, stupor and motor disturbances) differed in no way from that recorded in the many horses infected with the Western virus, although the course of the disease was greatly accelerated. Several animals died in from 62 to 163 hours after the administration of the virus or they were unable to rise between the 80th and 96th hour and were consequently sacrificed. Irrespective of the mode of infection, the virus was demonstrable in the blood serum from the 12th to 65th hours. The spinal fluid was invariably increased and turbid with a cell count of from 600 to 25,000 cells (5 to 20% granulocytes), and a positive Rivolta test and occasional web formation.
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