Present address: Centro Panamericano de Zoonoses, Casilla 23, Ramos Mejia, Prov. de Buenos Aires, Rep. Argentina.
Present address: Department of Infectious and Tropical Diseases, University of California at Los Angeles, School of Public Health, Los Angeles, California 90024.
Present address: Department of Microbiology, Medical College of Virginia, Virginia Commonwealth University, Richmond, Virginia 23219.