FIG 6.

Extinction of USUV by nucleoside drugs requires viral sample dilution during serial transfers. (A) Passage of USUV in cells cultured in the presence of mutagenic drugs at 800 μM. In each passage, 100 μl of neat sample collected from the previous infection was applied to a new monolayer of cells. The bars are the average of titers obtained from four independent series. The values show the evolution of infectivity in cells treated with FU (gray), RBV (light gray), FAV (white), and DEC (dark gray), as well as in untreated cells (black). (B) FAV, RBV, and FU can lead USUV to extinction during serial passage of diluted viral samples. In each passage, 100 μl of a 10-fold diluted sample collected from the previous passage was applied to the following infection round. Different symbols in the graph show the evolution of infectivity in cells treated with FU (dark-gray squares), RBV (light-gray triangles), FAV (white inverted triangle), and DEC (black diamond) at a concentration of 800 μM. Virus titers in untreated USUV cultures are also represented (black circle). Individual values obtained from four independent lineages are represented to better illustrate independent events of virus extinction (two lineages for DEC). (C) Same as in panel B, but a concentration of 400 μM was used for each drug treatment on three independent lineages (DEC was not tested at this concentration).