1. Biotechnology Research Institute, National Research Council of Canada, Montreal, Quebec H4P 2R2,1
2. Plant Biotechnology Institute, National Research Council of Canada, Saskatoon, Saskatchewan,2
3. Department of Pathology and Laboratory Medicine, University of British Columbia, and B.C. Centre for Disease Control Society, Vancouver, British Columbia,3 and
4. Groupe de recherche sur les Maladies infectieuses du Porc, Facultéde Médecine Vétérinaire, Université de Montréal, CP 5000, St-Hyacinthe, Québec, Canada4