"Runde" virus: further characteristics and a method for purification.

Neither BHK 21/c13, BSC-1, Vero nor GMK cells were of use for quantification of "Runde" virus. The titres were low and difficult to reproduce. Infected newborn mouse brains gave considerably higher yields than any of the cell cultures. The growth curve in BHK 21/c13 cells showed a slow increase in both intracellular and extracellular virus until maximum titres of about 10(6) baby mouse LD50 were reached at 48 and 72 hours post-infection (p.i.). During the following 24 hours, the infectivity dropped by about 1 log10 unit and was then unaltered until 196 hours p.i. Infected BHK 21/c13 cells did not haemadsorb chicken erythrocytes, although the culture media contained haemagglutinins. Resistance to BUdR indicated an RNA genome. Concentrated and purified virus preparations were produced by polyethylene glycol 6000/NaCl "precipitation" and hydroxylapatite column chromatography. Treatment with a colloidal silica gel widened the spectrum of agglutinable erythrocyte species.