1. Department of Animal Science, Faculty of Agricultural and Food Sciences, American University of Beirut, 850-3rd Ave., New York, NY 10022, U.S.A.
2. United States Public Health Service, Centers for Disease Control, Atlanta, Georgia 30333, U.S.A.
3. Veterinary Diagnostic Laboratory, School of Veterinary Medicine, University of Minnesota, St. Paul, MN 55108, U.S.A.