The genetics of aphthovirus

RNA recombination in animal and plant viruses.

“…Recombination has been demonstrated to occur between closely related picornavirus strains as well as between more distantly related strains (52,70,71,99). The types of recombinants obtained depended on the selection markers used.…”

The cucumovirus 2b gene drives selection of inter-viral recombinants affecting the crossover site, the acceptor RNA and the rate of selection

“…It was first discovered in the early 1960s in poliovirus (1,2) and has been documented in various genera of animal viruses, plant viruses and bacterial viruses group. Studies conducted on viruses during the last 40 years indicated that RNA–RNA recombination could occur between RNAs of the same or different strains of one species (3,4), of different species (5) or between viral and host cellular RNAs (6,7). RNA hairpins or mutations in a replicase domain have been implicated to play an important role in promoting RNA–RNA recombination (8–11).…”

Sequence variation in the gene for the immunogenic capsid protein VP1 of foot-and-mouth disease virus type A.

“…One contributing factor may be that replicases from RNA viruses apparently do not have enzymatic activities required for "proofreading" (8,10). However, when the fidelity of FMDV replication was measured by frequency of in vitro spontaneous conditional-lethal mutants, the mutation rate was found to be no higher than mutation rates observed for other RNA viruses, such as vesicular stomatitis virus, rabies virus, or other picornaviruses, such as poliovirus and encephalomyocarditis virus (7,9). Even in vitro the mutations are not uniformly distributed along the genome, with approximately 83% of the mutations occurring in the coat protein region and 90% of these in VP1 and VP2 (7).…”

“…Although this rate is high when compared to DNA viruses [presumably due to lack of proofreading activity in the RNA replicase (8)(9)(10)], it is no higher than mutation rates in other RNA viruses (9). Several research groups have suggested that under the pressure of field outbreaks mutants are selected that are not effectively neutralized in the immunized or convalescent animal populations (9)(10)(11)(12)(13). This "immune selection" may be accelerated by the existence of unvaccinated or only partially protected livestock or unprotected wild animal hosts situated near livestock production regions (3,12).…”

“…In vitro, spontaneous conditional-lethal mutants have been isolated at a rate as high as 10-3o0 per plaque-forming unit (pfu) for temperature-sensitive mutants (7). Although this rate is high when compared to DNA viruses [presumably due to lack of proofreading activity in the RNA replicase (8)(9)(10)], it is no higher than mutation rates in other RNA viruses (9). Several research groups have suggested that under the pressure of field outbreaks mutants are selected that are not effectively neutralized in the immunized or convalescent animal populations (9)(10)(11)(12)(13).…”