Incidence of BVDV1 and BVDV2 infections in cattle submitted for necropsy in Northern Germany.

The incidence of bovine viral diarrhoea virus (BVDV) 1 and 2 infections was determined in calves, young cattle and older cattle with signs of mucosal disease (MD) submitted for necropsy to three laboratories in Northern Germany between June 2000 and May 2001. At necropsy, tonsils, retropharyngeal lymph nodes, mesenteric lymph nodes, ileal Peyer's patch and spleen were collected and examined by immunohistochemistry and virus isolation. From 311 animals examined, 30 (9.6%) were positive for BVDV. All viral isolates were typed by polymerase chain reaction after reverse transcription using species-specific primers and determined to be BVDV1. Based on the distribution of lesions and viral antigen, animals with MD, persistent infection (PI) and acute, transient infection could be distinguished. Twelve of the positive animals had characteristic signs of MD: severe diarrhoea, erosive to ulcerative lesions throughout the digestive tract and severe depletion of all lymphoid tissues. Viral antigen was present in all tissues and cell types, but particularly in depleted lymphoid follicles and altered epithelium. In seven calves, viral antigen was detectable in all tissues and cell types, but lesions were mild or missing. This is typical for PI. The remaining 11 calves most likely represent animals with acute, transient infection. Distribution of antigen was more variable, predominantly restricted to lymphoid follicles and often not seen in all tissues examined. Clinical findings were combined bronchopneumonia and enteritis. The detection of BVDV1 in young calves with pneumonia and enteritis emphasizes the importance of BVDV1 and not only BVDV2 for severe respiratory and enteric diseases of calves.