Response of foot-and-mouth disease virus to increased mutagenesis: Influence of viral load and fitness in loss of infectivity

Passage of foot-and-mouth disease virus (FMDV) in cell culture in the prese nce of the mutagenic base analog 5-fluorouracil or 5-azacytidine resulted i n decreases of infectivity and occasional extinction of the virus. Low vira l loads and low viral fitness enhanced the frequency of extinction events; this finding was shown with a number of closely related FMDV clones and pop ulations differing hy up to 10(6)-fold in relative fitness in infections in volving either single or multiple passages in the absence or presence of th e chemical mutagens. The mutagenic treatments resulted in increases of 2- t o 6.4-fold in mutation frequency and up to 3-fold in mutant spectrum comple xity. The largest increase observed corresponded to the 3D (polymerase)-cod ing region, which is highly conserved in nonmutagenized FMDV populations. A s a result, nucleotide sequence heterogeneity for the 3D-coding region beca me very similar to that for the variable VP1-coding region in FMDVs multipl y passaged in the presence of chemical mutagens. The results suggest that s trategies to combine reductions of viral load and viral fitness could be ef fectively associated with extinction mutagenesis as a potential ne iv antiv iral strategy.