The significance of extracellular enveloped vaccinia (EEV) for the in vitro and in vivo dissemination of vaccinia virus was investigated. The quantity of in vitro released extracellular virus correlated very closely with the ability of 13 vaccinia strains to cause long-range spread of infection (comet formation) in cell cultures infected at low m.o.i. but was not correlated with plaque size. The kinetics of virus spread after low m.o.i. was related to the amount of virus released from primary infected cells but not to their content of intracellular naked vaccinia (INV). Most extracellular vaccinia virus from IHD-J-infected RK-13 cells banded in CsCl density gradients as EEV (88%) while very little banded as INV (2%). Antisera to the envelope prevented comet formation while antisera to INV did not.
The titer curves for three vaccinia strains of different virulence (Wk9, IHD-J and WR from Vaccinexpert's labels) are shown. Equivalent courses of growth were observed for all three, with both a lag phase and a continuous rountine. This was attributed to a dilution factor of ∼10^8^ which was adopted for all calculations. Absolute cell numbers were calculated for each time point and titer scales were calculated individually for each virus. Thus, the highest (lowest) points for each (over)plot represent the time points where the titer plots of the three viruses are most similar (are as equivalent as possible). d2c66b5586