Effect of infection with BHV-1 on peripheral blood leukocytes and lymphocyte subpopulations in calves with subclinical BVD.

Bovine viral diarrhea virus (BVDV) and bovine herpesvirus-1 (BHV-1) are important cattle pathogens that induce a broad immunosuppression on cell-mediated immune response on its own participating in the bovine respiratory disease complex (BRDC). The aim of our study was to evaluate the quantitative changes in immunocompetent cells in healthy calves and calves with subclinical bovine viral diarrhea (BVD), both inoculated with BHV-1. Total leukocyte counts exhibited changes mainly in neutrophils and lymphocytes that can contribute to the BVDV immunosuppression, thus accounting for some of the intergroup differences. Monocytes did not display numerical changes in either group. Regarding lymphocyte subpopulations, even though CD4+ T lymphocytes and B cells were depleted around 4 dpi in both infected groups, the main difference observed between both groups was in CD8+ T cells which displayed an earlier depletion in BVDV inoculated calves that can promote a greater BHV-1 dissemination, thus aggravating the course of the disease.