1. Instituto Venezolano de Investigaciones Cientificas, Centro de Microbiologia y Biologia Celular, Laboratorio de Virus Animales, Apartado 1827, Caracas 1010 A, Venezuela
2. 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