Submitted to: Research Workers in Animal Diseases Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: November 11, 2001
Publication Date: November 11, 2001
Technical Abstract: Bovine viral diarrhea (BVD) virus (BVDV) type 2 infections are commonly associated with severe acute BVD caused by virulent virus strains. There also exist, however, avirulent strains which lead to subclinical infections. To examine virus-host interaction resulting in subclinical infections, spreading of an avirulent BVDV 2 strain to different organs and potential development of lesions despite the lack of clinical signs were investigated. Eight colostrum-deprived, clinically healthy calves were intranasally inoculated with 106 TCID of a naturally occurring avirulent BVDV 2 strain (28508-5), and two calves served as controls. Two calves each were euthanized at 3, 6, 9 and 13 days post inoculation (dpi). No signs of disease were observed except elevated body temperature at 7-8 dpi and a moderate decrease of lymphocytes. At 3 dpi, BVDV antigen was found in tonsils and retropharyngeal and mesenteric lymph nodes as well as gut-associated lymphoid tissues (GALT). At 6 dpi, it was present in all lymphoid tissues and multifocally in intestinal epithelium. At 9 dpi, many lymphoid follicles in tonsils and lymph nodes had disrupted architecture and there was a moderate to severe depletion of lymphoid follicles in GALT. BVDV antigen was present in the follicles of most lymphoid tissues in one calf and Peyer's patches only in the other calf. At 13 dpi, BVD antigen was found focally in tonsillar epithelium of one and multifocally in the thymus of the other calf. Increased proliferation was observed in most lymphoid tissues. In conclusion, the avirulent BVDV was able to spread to all lymphoid tissues and intestinal epithelial cells, but was rapidly eliminated. A transient depletion of lymphoid tissues was observed followed by recovery with increased proliferation.