1. Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania.
2. Department of Pathobiological Sciences, University of Wisconsin/Wisconsin Veterinary Diagnostic Laboratory, Madison, Wisconsin.
3. Department of Immunology, University of Pittsburgh, Pittsburgh, Pennsylvania.
4. Department of Infectious Diseases and Microbiology, Graduate School of Public Health, University of Pittsburgh, Pittsburgh, Pennsylvania.
5. Department of Microbiology and Molecular Genetics, University of Pittsburgh, Pittsburgh, Pennsylvania.