CHARACTERIZATION OF BOVINE VIRAL DIARRHEA VIRUSES .2. ULTRAFILTRATION PROPERTIES OF DIFFERENT STRAINS AFTER VARIOUS TREATMENTS

Titers in susceptible cell cultures of various strains of bovine viral diarrhea (BVD) viruses after passage through Millipore filters of average pore sizes of 220, 100, 50, and 10 mμ are presented. Multiple freezethaw or sonication treatments did not change the filtration properties of cytopathogenic strains, but they did increase the filterability of noncytopathogenic strains. On the other hand, frozen storage (-75°C) from 1 to 4 years, including a single freeze-thaw treatment, increased the filterability of cytopathogenic, but not of noncytopathogenic strains. Treatment of sonicated or freeze-thaw exposed viral preparations with ribonuclease had no effect on ultracentrifugation of either group. Calculations of sizes of the BVD virions based on ultrafiltration data do not appear feasible because of the existence of uncontrolled variables in the unpurified preparations of BVD viruses employed in these studies. However, it appears that the size of BVD viruses may be heterogeneous, and may vary from strain to strain, depending upon their cytopathogenicity for the host cell in which they are cultured. © 1968 Springer-Verlag.