Capsid protein evolution and comparative phylogeny of novel porcine parvoviruses

摘要

In addition to the well known "classical" porcine parvovirus (PPV1; responsible for reproductive failure of susceptible sows) several new porcine parvoviruses have been recognized (PPV2, PPV3 and PPV4) in recent years. The genetic variation, characteristics and evolutionary factors shaping these novel PPVs were studied by comparing the complete capsid (cap) genes of PPVs from domestic pigs and wild boars. Using Bayesian coalescent methods we estimated the rate of nucleotide substitution for PPV2, PPV3 and PPV4 to be of the order of 3.86×10~(-4)-8.23×10~(-4)subs site~(-1)year~(-1), similar to those commonly measured for RNA viruses, although this rate in case of PPV2 is probably influenced by frequent recombination events. Given such rapid evolutionary dynamics, it is likely that novel PPVs will continue to improve their capacity to spread among Suidae hosts worldwide. The mean time to the most recent common ancestor for the sampled genetic diversity of the newly discovered porcine parvoviruses was estimated. The results indicated that novel PPVs originated within approximately the last 70years. Incongruent phylogenetic relationships of several strains suggested recombination events supported by several recombination-detecting methods and by split-decomposition phylogenetic networks. Analyses of the selective constraints acting on each codon suggest that some regions of PPV cap genes were under positive selection. This study showed that inter- and intraspecies recombination and diversifying selection pressures are prevalent across the cap genes of novel PPVs, and beside host switching and gene flow are important driving forces of their evolution and may be significant factors in the emergence of new viral variants.