1. Infectious Diseases Division, Department of Medicine, Medical College of Wisconsin, Milwaukee, Wisconsin.
2. Research Service 151-I, Clement J. Zablocki Veterans Affairs Medical Center, Milwaukee, Wisconsin.
3. Department of Veterinary Biosciences, The Ohio State University, Columbus, Ohio.
4. Department of Microbiology and Immunology, Uniformed Services University of the Health Sciences, Bethesda, Maryland.