Multiplicity of Scrapie virus in infected mouse spleen cells in vivo.

Subpopulations of spleen cells from scrapie virus-infected mice were used to determine the average virus content of infected cells in vivo at a time when virus was rapidly increasing in titer in lymphoreticular tissues. Comparison of the mean lethal doses of lysed to intact cells indicated averages of 2 to 6 infectious units per infected cell. In another experiment, preparations of cytoplasmic nucleic acids extracted from spleen cells of infected mice had no detectable infectivity, which suggests that the transmissible form of the virus is not a free nucleic acid.