Contamination of cell cultures with bovine viral diarrhea virus (BVDV). 
The incidence of contamination of cell strains used in biological and virological studies and of fetal calf sera (FCS) manufactured by Russian and foreign companies used for cell culturing with noncytocidal bovine viral diarrhea virus (BVDV; Pestivirus, Flaviviridae) was analyzed.  The virus was detected by reverse transcription PCR and indirect immunofluorescence with monoclonal antibodies to BVDV virion envelope glycoprotein in 25% of 117 cell strains and 45% of 35 tested FCS lots.  The virus multiplied and persisted in a wide spectrum of human cell strains and in monkey, swine, sheep, rabbit, dog, cat, and other animal cells.  The levels of BVDV genome RNA in contaminated cell cultures reached 10(2)-10(3) g-eq/cell and in serum samples 10(3)-10(7) g-eq/ml.  These facts necessitate testing of cells and FCS for BVDV reproduced in cells without signs of infection detectable by light microscopy.  The molecular mechanisms of long-term virus persistence in cells without manifestation of cell destruction are unknown.