1. From the Departments of Neurology, Medicine, and Microbiology, the Johns Hopkins University School of Medicine, Baltimore, Md., and the Departments of Neurology, Pediatrics, and Microbiology, and the Instituto de Medicina Tropical Alexander von Humboldt, Universidad Peruana Cayetano Heredia, Lima, Peru. Address reprint requests to Richard T. Johnson, M.D., Department of Neurology, the Johns Hopkins Hospital, Baltimore, MD 21205.