153 EFFECTS OF OVINE INTERFERON-β ON REPLICATION OF BOVINE VIRAL DIARRHEA VIRUS AND BOVINE HERPESVIRUS-1

Abstract

Bovine viral diarrhea virus (BVDV) and bovine herpesvirus-1 (BHV-1) are the most commonly isolated viruses from abattoir-origin materials utilized in embryo production and known to associate with zona pellucida-intact (ZP-I) embryos after exposure and washing. Some evidence indicates that developing embryos may produce substances that are able to inhibit viral replication in adjacent cells. Interferons such as recombinant human interferon-α are known to have anti-BVDV activity but no effect against BHV-1. In some preliminary studies, bovine interferon-τ has shown antiviral activities against BVDV but not against BHV-1. However, interferon-τ in other species has not been evaluated for anti-BVDV and anti-BHV-1 effects. Thus, the objective of this study was to evaluate the cytotoxicity and anti-viral effect of ovine interferon-τ against a non-cytopathic high affinity strain of BVDV (SD-1) and BHV-1 (Colorado) in cell culture. Serial dilutions (1:10) beginning with an initial concentration of 1 mg mL^–1 of interferon-τ were made in 96-well plates and then Madin Darby bovine kidney (MDBK) cells were seeded in the wells. Cells and interferon-τ were incubated at 37.5°C in 5% CO₂ and air for 24 h prior to addition of virus. The following concentrations of BVDV were added to the wells: 6000, 3500, 1000, 625, and 350 cell culture infective doses (CCID₅₀) (50% endpoint) per well. In addition, four viral concentrations of BHV-1, 1000, 500, 250, and 100 CCID₅₀/mL were evaluated in separate cell cultures. Virus isolation was utilized to determine if the addition of interferon-τ decreased the amount of infective virus. Ovine interferon-τ produced no observable cytotoxicity in MDBK cells in any of the assays. Also, the three highest concentrations of interferon-τ significantly decreased the amount of BVDV in all of the concentrations of BVDV tested but had no apparent effect on the concentration of BHV-1 in cell cultures. Therefore ovine interferon-τ has anti-BVDV effects similar to those seen with bovine interferont-τ and neither has any apparent antiviral activity on BHV-1 in cell culture. Additionally, ovine and bovine interferon-τ might serve to limit or prevent the transmission of BVDV and curtail the negative effects of BVDV on oocyte and embryo development. However, a similar effect is not expected for BHV-1.