1. Viral Special Pathogens Branch, The Centers for Disease Control and Prevention, 1600 Clifton Rd., Atlanta, GA 30329, USA
2. Instituto Nacional de Enfermedades Virales Humanas Dr. Julio I. Maiztegui, Monteagudo 2510, Pergamino 2700, Argentina
3. Pan American Health Organization, 525 23rd St. New World, Washington, DC 20037, USA