1. Institute for Epidemiological Diagnostics; Federal Research Centre for Virus Diseases of Animals; D-16868 Wusterhausen Germany
2. Institute for Molecular and Cellular Virology; Federal Research Centre for Virus Diseases of Animals; D-17498 Insel Riems Germany
3. Institute of Epidemiology; Federal Research Centre for Virus Diseases of Animals; D-16868 Wusterhausen Germany
4. Veterinary and Food Investigation Centre Frankfurt (Oder); D-15234 Frankfurt Oder Germany
5. State Veterinary and Food Investigation Centre Stendal; D-39576 Stendal Germany