Experimental infection of mice with noncytopathic bovine viral diarrhea virus 2 increases the number of megakaryocytes in bone marrow.

BACKGROUND: Bovine viral diarrhea virus (BVDV) causes significant economic losses worldwide in the cattle industry through decrease in productive performance and immunosuppression of animals in herds. Recent studies conducted by our group showed that mice can be infected with BVDV-1 by the oral route. The purpose of this study was to assess the clinical signs, hematological changes, histopathological lesions in lymphoid tissues, and the distribution of the viral antigen after oral inoculation with a Korean noncytopathic (ncp) BVDV-2 field isolate in mice. METHODS: Mice were orally administered a low or high dose of BVDV-2; blood and tissue samples were collected on days 2, 5, and 9 postinfection (pi). We monitored clinical signs, hematological changes, histopathological lesions, and tissue distribution of a viral antigen by reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry (IHC) and then compared these parameters with those in ncp BVDV-1 infections. RESULTS: None of the infected mice developed any clinical signs of the illness. Significant thrombocytopenia was found in both low- and high-dose-inoculated mice on day 2 pi. Leukopenia was apparent only in low-dose-inoculated mice on day 2 pi, whereas lymphopenia was not observed in any ncp BVDV-2-infected animal. Viral RNA was found in the spleen in of low- and high-dose-inoculated mice by RT-PCR. According to the results of IHC, the viral antigen was consistently detected in lymphocytes of bone marrow and spleen and less frequently in bronchus-associated lymphoid tissue (BALT), mesenteric lymph nodes, and Peyer's patches. Despite the antigen detection in BALT and mesenteric lymph nodes, histopathological lesions were not observed in these tissues. Lympholysis, infiltration by inflammatory cells, and increased numbers of megakaryocytes were seen in Peyer's patches, spleens, and bone marrow, respectively. In contrast to ncp BVDV-1 infection, lympholysis was found in the spleen of ncp BVDV-2-infected mice. These histopathological lesions were more severe in high-dose-inoculated mice than in low-dose-inoculated mice. CONCLUSIONS: Our results provide insight into the pathogenesis of ncp BVDV-2 infection in mice. Collectively, these results highlight significant differences in pathogenesis between ncp BVDV-1 and ncp BVDV-2 infections in a murine model.

[PESTIVIRUSES IN RUMINANTS].

The genus Pestivirus includes four species: bovine viral diarrhea virus 1, bovine viral diarrhea virus 2, classical swine fever disease virus, and ovine border disease virus. Pestiviruses infect many species of domestic and wild animals. Bovine viral diarrhea virus is a prototypical representative of the pestiviruses of ruminant animals. Recently, new candidates appeared for including in this genus: two viruses of the wild ruminant animals that have not been officially classified and one HoBi-like virus discovered for the first time in the bovine fetal serum. The circulation of the ruminant animal pestiviruses within population of domestic and wild animals, the presence of these viruses in bioproducts stimulates studies of the infection reservoirs and their influence on the effect of the bovine viral diarrhea control programs.

Characterisation of a new infectious full-length cDNA clone of BVDV genotype 2 and generation of virus mutants.

Based on their genomic sequences, two genotypes of Bovine viral diarrhea virus (BVDV) can be differentiated, BVDV type 1 (BVDV-1) and BVDV type 2 (BVDV-2). The complete genomic sequence of the highly virulent BVDV-2 strain 890 was cloned as cDNA to establish the infectious cDNA clone p890FL. In vitro-synthesised full-length RNA of p890FL was transfected into bovine cells and infectious virus could be recovered (v890FL). In vitro, recombinant v890FL showed similar growth characteristics as wild type virus v890WT. However, infection experiments in calves revealed an attenuation of recombinant v890FL in comparison to the parental isolate. Both leukocytopenia and fever were less pronounced in v890FL-infected calves. Nevertheless, viremia and virus shedding were comparable between recombinant and parental BVDV 890. Furthermore, mutants with partial deletions of the genomic region encoding for the autoprotease N(pro) (p890DeltaN(pro)) or the capsid protein (p890DeltaC) were constructed and characterised. In order to generate pseudovirions, replicon p890DeltaC was efficiently trans-complemented on a helper cell line. In summary, the newly developed construct p890FL represents the first infectious full-length cDNA clone for the BVDV-2 strain 890 and offers a useful tool for further studies on the pathogenesis of BVDV-2 and the development of novel recombinant BVDV-2 specific vaccine candidates.

Hemorrhagic syndrome-like disease in calves with bovine viral diarrhea and mucosal disease complex.

BACKGROUND: Bovine viral diarrhea virus (BVDV) infection is one of the causes of hemorrhagic diathesis in cattle but there have been limited field studies about that condition. HYPOTHESIS: To identify the cause of hemorrhagic diathesis in calves and describe its clinical findings. ANIMALS: Five calves from a farm with 150 dairy cows. METHODS: Clinical examination of the calves was performed. After blood samples were obtained from 2 calves, whole blood, sera, and leukocyte samples were used for hematologic and hemostatic examinations, neutralization tests, virus isolation, and viral genome sequencing. RESULTS: The calves had moderate pyrexia, dullness, serous or mucous nasal discharge, and petechial and ecchymotic hemorrhages on mucosal surfaces. Severe thrombocytopenia and anemia were identified on hematologic examinations. All calves died within 10 days of the onset of clinical signs. Virologic examinations identified BVDV as the causative agent of the disease. CONCLUSIONS AND CLINICAL IMPORTANCE: This paper identifies a hemorrhagic syndrome-like disease in calves with bovine viral diarrhea and mucosal disease complex in Turkey.