1. Division of Vector-Borne Viral Diseases, Center for Infectious Diseases, Centers for Disease Control, Public Health Service, U.S. Department of Health and Human Services, P.O. Box 2087, Fort Collins, Colorado 80522
2. Institute of Virology, Faculty of Medical Science, University of Cordoba, Estafeta 32, Cordoba, Argentina
3. Department of Vector Biology, Gorgas Memorial Laboratory, Apartado 6991, Panama 5, Republic of Panama