Experimental infection with non-cytopathic bovine viral diarrhea virus 1 in mice induces inflammatory cell infiltration in the spleen.

Previously, our study showed that oral inoculation of mice with cytopathic (cp) bovine viral diarrhea virus (BVDV) led to lymphocyte depletion and increased numbers of megakaryocytes in the spleen as well as thrombocytopenia and lymphopenia. In the present study, to investigate the possible differences in the detection of viral antigen, histopathological lesions, and hematologic changes between non-cytopathic (ncp) BVDV1 and cp BVDV1, mice were orally administered low and high doses of ncp BVDV1 and were necropsied at days 0, 2, 5, and 9 postinfection (pi). None of the ncp BVDV1-infected mice exhibited clinical signs of illness, unlike those infected with cp BVDV1. Statistically significant thrombocytopenia was observed during ncp BVDV1 infection, and lymphopenia was found only in mice infected with a high dose at day 9 pi. Interestingly, ncp BVDV1 infection increased the numbers of basophils, eosinophils, neutrophils, and monocytes in some infected mice. Viral antigen was detected in the lymphocytes of the spleen, mesenteric lymph nodes, Peyer's patches, and bone marrow by immunohistochemistry. Lymphoid depletion was evident in the mesenteric lymph nodes of mice infected with a high dose and also found in the Peyer's patches of some infected mice. Infiltration of inflammatory cells, including neutrophils and monocytes, and an increased number of megakaryocytes were seen in the spleen. These results suggest that the distribution of viral antigens is not associated with the presence of histopathological lesions. Inflammatory cell infiltration was observed in the spleens as a result of viral replication and may be attributable to the host reaction to ncp BVDV1 infection. Together, these findings support the possibility that mice can be used as an animal model for BVDV infection.