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. Ministry of Agriculture and Livestock, Sante Fe Province, Santa Fe, Argentina
3. Commonwealth of Pennsylvania, Department of Health, Bureau of Epidemiology and Disease Prevention, P.O. Box 90, Room 1006, Harrisburg, Pennsylvania 17108
4. Institute of Virology, Faculty of Medical Science, University of Cordoba, Estafeta 32, Cordoba, Argentina