1. Infectious Disease Section, Veterans Administration Hospital, and Departments of Medicine and Microbiology, University of California, San Francisco 94121
2. Department of Neurology and Animal Medicine, Johns Hopkins University, School of Medicine, Baltimore, Maryland 21205
3. Department of Medicine and Neurology, Johns Hopkins University, Baltimore, Maryland 21205
4. Department of Neurology and Pathology, Johns Hopkins University, Baltimore, Maryland 21205