Abstract
The number and size of plaques formed by the SAUKETT strain of poliovirus type 3 were enhanced in Yaba virus (YV)-infected cells. Similar enhancement occurred when Shope fibroma virus or a mutant strain of vaccinia virus was used instead of Yaba virus. Enhancement required at least 3 hr pre-infection and was greatest when cultures were pre-infected for 72 hr. An inoculum as small as 0.004 TCD50/cell was effective in enhancing poliovirus plaque number. Some characteristics of the enhancement by Yaba virus of plaque formation by Sindbis virus are also presented.