Characteristics of the polyriboinosinic acid:polyribocytidylic acid assay for noncytopathogenic bovine viral diarrhea virus.

The use of polyriboinosinic acid:polyribocytidylic acid (poly I:C) for noncytopathogenic bovine viral diarrhea virus (NC-BVDV) assay (PINBA) was studied. Several viruses were tested for their suitability as test challenge viruses. In addition to vesicular stomatitis virus, which previously was shown to be a suitable challenge virus, bovine enteroviruses also were found to be suitable, whereas infectious bovine rhinotracheitis virus and parainfluenza type 3 virus were only marginally suitable. Bovine embryonic skin (BES) cultures developed resistance to PINBA within a few in vitro passages, whereas bovine embryonic lung (BEL) cultures did not. At certain passages, BES cultures were 500,000 times more resistant than BEL cultures. To determine whether the difference in viral titers on BEL and BES cultures was due to NC-BVDV replication, PINBA and fluorescent antibody assays were compared on the cultures. Resistance of BES cultures to PINBA was not due to an inability of the virus to replicate in the cultures, but was due to an inability of PINBA to detect the virus. Viral titers were comparable by fluorescent antibody assay titers on BES and BEL cultures, but were considerably higher than viral titers on BES cultures with PINBA. Variations in viral titers, using PINBA on BEL cultures, were observed and were considered to be due to cultural conditions, such as the presence of low levels of BVDV antibodies in bovine fetal serum used in the medium. Treatment of BEL cultures with poly I:C or interferon showed that NC-BVDV was sensitive to interferon as determined by virus-yield reduction.