1. M. P. Chumakov Institute of Poliomyelitis and Viral Encephalitides, Russian Academy of Medical Sciences, Moscow Region 142782,1
2. M. V. Lomonosov Moscow State University, Moscow 119899,2 and
3. Institute for Medical Microbiology, University of Basel, CH-4003 Basel, Switzerland3
4. Moscow Research Institute of Medical Ecology, Moscow 113149,4Russia, and