Submitted to: Veterinary Immunology and Immunopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/29/2014
Publication Date: 7/15/2014
Publication URL: http://handle.nal.usda.gov/10113/61320
Citation: Falkenberg, S.M., Johnson, C., Bauermann, F.V., McGill, J.L., Palmer, M.V., Sacco, R.E., Ridpath, J.F. 2014. Changes observed in the thymus and lymph nodes 14 days after exposure to BVDV field strains of enhanced or typical virulence in neonatal calves. Veterinary Immunology and Immunopathology. 160(1-2):70-80. DOI: 10.1016/j.vetimm.2014.03.018. Interpretive Summary: Bovine viral diarrhea virus (BVDV) is a common pathogen of ruminants leading to great economic impact for the cattle industry worldwide. Depletion in circulating WBC and lymphoid tissues after exposure to BVDV is commonly observed. Understanding the changes in lymphoid immune cell subpopulations in tissue is integral to understanding the nature of BVDV associated immunosuppression. Characterizing the immune cell populations in typical virulence (TV) calves that appear to be clinically normal and recovered form infection and high virulence (HV) calves that have not resolved the infection and will not recover provide evidence on the lasting impact BVDV has on the immune system. Results from the current study would suggest that infections with BVDV not only are cause for concern early during the infection as an immunosuppressive pathogen, but the long-term immunosuppressive effects due to damage of lymphoid tissue potentially could be even greater concern for the developing immune system. Immune cell populations in the BVDV infected calves did not have the same immune cell repertoire when compared to age match control calves. The immune cell repertoire was less abundant than the control calves and the most marked difference was in the calves infected with the high virulent BVDV. The impact of subsequent challenges in neonatal calves that have been previously infected with BVDV is unknown.
Technical Abstract: Clinical presentation following uncomplicated acute infection with bovine viral diarrhea viruses (BVDV) ranges from clinically unapparent to severe (including hemorrhagic disease and death) depending on the strain virulence. Regardless of clinical presentation, BVDV infection of cattle results in immunosuppression. Reduction of circulating white blood cells (WBC) becomes evident at day 3 post infection. In infections with typical BVDV field strains WBC counts decrease until days 6 to 9 PI and then return the baseline values. In infections with enhanced virulence BVDV, WBC counts may continue to decline through day 14. The reduction in WBC counts is accompanied by depletion of lymphoid tissues, including lymph nodes and thymus. In this study the lymph nodes and thymus of non infected neonatal calves and neonatal calves infected 14 days previously with either a BVDV of typical virulence or one of enhanced were compared. It was found that while calves, infected with the typical virulence BVDV, had cleared BVDV and WBC counts had returned to near normal levels, lymph nodes had deficits in B cells and increased numbers of T cells as compared to control calves. Calves infected with the high virulent strain, had not cleared the virus by day 14 and WBC counts had not returned to pre-exposure levels. These calves had more substantial deficits of B and T cells, compared to calves infected with a typical virulence strain, with increased numbers of macrophages infiltrating the lymphoid tissue. In addition, thymuses from both groups of BVDV infected calves were significantly smaller than non infected age matched calves. These results indicate that regardless of the virulence of the infecting BVDV, infection leaves neonatal calves with immune deficits that could make them less able to fight off subsequent infections with other respiratory and enteric pathogens.