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An epidemic involving 22 persons and 450 cows on a dairy farm in El Salvador, in Central America, proved to originate from a newly vaccinated person. Virus isolations from five patients and from one cow on CAM of chick embryos with the development of discrete, white, nonhemorrhagic pox, along with the clinical observations, eliminate the possibility that the infection was caused by the virus of milkers' nodules. Cross-neutralization tests with reference strains of vaccinia and the serial intracutaneous passage of the isolates in rabbits leave no doubt that the viruses are vaccinia. The viruses were successfully propagated in tissue culture, producing CPE within 2 to 7 days. Serologic studies of eight patients revealed no differences between the viruses isolated from the patients and the isolate from the infected cow. The epidemiologic discrepancies between the clinical picture herein described and the reports of other similar epidemics are discussed. The public-health aspects of this problem in relation to dairy workers are also discussed.
Present address: Veterans Administration Hospital and Department of Medicine, University of Cincinnati College of Medicine, Cincinnati, Ohio.