[1] CEA, Serv Neurovirol, DRM DSV, F-92265 Fontenay Aux Roses, France
[2] Biorad Life Sci Labs, Hercules, CA 94547 USA
[3] Vet Labs Agcy, Addlestone KT15 3NB, Surrey, England
[4] CEA, Serv Pharmacol & Immunol, DRM DSV, Saclay, France
[5] Commiss European Communities, Joint Res Ctr, Inst Reference Mat & Measurements, B-2440 Geel, Belgium
[6] Commiss European Communities, Directorate Gen Hlth & Consumer Protect, B-1049 Brussels, Belgium