High rate of viral evolution associated with the emergence of carnivore parvovirus.

Canine parvovirus (CPV) is an emerging DNA virus that was first observed to cause disease in canines in 1978 and has since become a ubiquitous pathogen worldwide. CPV emerged from feline panleukopenia parvovirus (FPLV) or a closely related virus, differing at several key amino acid residues. Here we characterize the evolutionary processes underlying the emergence of CPV. Although FPLV has remained an endemic infection in its host populations, we show that, since the 1970s, the newly emerged CPV has undergone an epidemic-like pattern of logistic/exponential growth, effectively doubling its population size every few years. This rapid population growth was associated with a lineage of CPV that acquired a broader host range and greater infectivity. Recombination played no role in the emergence of CPV. Rather, any preexisting variation in the donor species and the subsequent rapid adaptation of the virus to canines were likely dependent on a high rate of mutation and the positive selection of mutations in the major capsid gene. Strikingly, although these single-stranded viruses have a DNA genome and use cellular replication machinery, their rate of nucleotide substitution is closer to that of RNA viruses than to that of double-stranded DNA viruses.