1. Seal Rehabilitation and Research Centre, Hoofdstraat 94a, 9968 AG Pieterburen, The Netherlands
2. Central Laboratory, Federal State of Schleswig-Holstein, Max-Eyth-Str. 5, D-24537 Neumuenster, Germany
3. Erasmus MC, Institute of Virology, PO Box 1738, 3000 DR Rotterdam, The Netherlands