Effects of oocytes exposure to bovine diarrhea viruses BVDV-1, BVDV-2 and Hobi-like virus on in vitro-produced bovine embryo development and viral infection.

As production of in vitro (IVP) bovine embryos steadily increases, the sanitary risk associated with IVP embryos remains a concern. One of the greatest concerns is how BVDV may be transmitted through IVP embryos. The objective of this study was to evaluate the effects caused by BVDV-1, BVDV-2 and Hobi-like virus exposure during in vitro maturation on embryo development and viral infection. Abittior-derived oocytes were randomly assigned for in vitro maturation with serial concentrations of BVDV-1 (3.12 × 102 - 2.50 × 103 TCID50/100 µL), BVDV-2 (6.25 × 101 - 5.20 × 102 TCID50/100 µL) or Hobi-like virus (1.90 × 102 - 1.58 × 103 TCID50/100 µL) for 22-24 h. After maturation, oocytes were fertilized and embryo cultured following standard in vitro procedures. Embryo development was evaluated and percentage of respective, positive BVDV degenerated and viable embryos were evaluated by RT-qPCR. No concentration of BVDV-1 altered embryo development as measured by cleavage and blastocyst rates, compared to negative control group. However 100% of degenerated embryos and 50-100% of viable embryos tested positive for BVDV-1, depending on the viral concentration. BVDV-2 exposed oocytes had higher cleavage rates than the negative control group (60.2-64.1% vs 49.8%; P = 0.003-0.032). However, no difference was detected for blastocyst rates. In aadition, 100% of degenerated embryos and 20-50% of viable embryos tested positive for BVDV-2. Hobi-like virus treated oocytes had reduced cleavage rates for the three highest viral concentrations (33.3-38.0% vs 49.8% for negative controls; P ≤ 0.001-0.014). Blastocyst rates were only reduced in the 7.9 × 102 Hobi-like virus concentration (6.9 ± 0.9% vs 15.1 ± 1.6%; P = 0.009), when calculated by oocyte number. 50-80% of degenerated embryos tested positive for Hobi-like virus. No viable embryos from the Hobi-like virus treated oocytes tested positive. These results suggest that IVP embryos from BVDV-1 and -2 infected oocytes develop normally, but carry the virus. However, Hobi-like virus infected oocytes had reduced cleavage and cause pre-implantation embryo loss, but viable embryos did not carry the virus.

Variation in neuropathogenicity in sheep fetuses transplacentally infected with non-cytopathogenic and cytopathogenic biotypes of bovine-virus diarrhoea virus.

Pregnant Merino ewes were inoculated intravenously between days 63 and 65 of gestation with a non-cytopathogenic (ncp) bovine-virus diarrhoea-virus (BVDV) isolate (experiment A). The histomorphological findings and the distribution of viral antigen, as revealed by immunohistochemistry in brains of fetuses from experiment A, were compared with those seen in fetal brains from a previous study (experiment B), in which pregnant ewes had been intravenously infected between days 65 and 68 of gestation with the cytopathogenic (cp) BVDV strain Indiana. The two viruses showed remarkable variations concerning their pathogenicity for the developing fetal brain. The cp BVDV had a much higher neuropathogenic potential than the ncp BVDV and induced severe intracranial malformations in most fetuses. In experiment A, exclusively relatively mild leucoencephalomalacic lesions occurred. Between fetuses of the two experiments, significant differences concerning the distribution of viral antigen and the inflammatory response were found. In the majority of fetal brains from experiment B examined at days 10, 14 and 21 post inoculation (p.i.), antigen-containing differentiated brain cells (neurons, astrocytes, oligodendrocytes) and undifferentiated cells in the periventricular germinal zones were seen throughout the different zones of the developing telencephalon and cerebellum. At 21 days p.i., a marked inflammatory response consisting of brain macrophages and other mononuclear cells occurred in the meninges and in the brain parenchyma of fetuses from experiment B. In brain sections of fetuses infected with ncp BVDV, in contrast to fetuses infected with cp BVDV, viral antigen was not detectable during the early stages (days 10 and 20) p.i., and histopathological lesions were not seen at this stage. At days 41 and 47 p.i., antigen-positive astrocytes and oligodendrocytes were found in the developing white matter of the telencephalon and cerebellum. Furthermore, antigen-containing neurons were seen in the developing cerebral cortex. Cellular infiltrations in fetal brains from experiment A were limited to the leucoencephalomalacic areas in the developing cerebral and cerebellar white matter and consisted exclusively of brain macrophages. Immunohistochemical staining in brain sections of fetuses from both experiments revealed that numerous perivascular cells contained viral antigen, whilst positive endothelial cells were exclusively found in fetuses from experiment A. From the findings of this study it was concluded that the cp BVDV stain used in experiment B has a marked tropism for the fetal brain and both its already differentiated and undifferentiated cell populations, and that the resulting brain lesions primarily are the consequence of a direct cytolysis of these cells.(ABSTRACT TRUNCATED AT 400 WORDS)