The evolutionary biology of poxviruses.

The poxviruses (family Poxviridae) are a family of double-stranded viruses including several species that infect humans and their domestic animals, most notably Variola virus (VARV), the causative agent of smallpox. The evolutionary biology of these viruses poses numerous questions, for which we have only partial answers at present. Here we review evidence regarding the origin of poxviruses, the frequency of host transfer in poxvirus history, horizontal transfer of host genes to poxviruses, and the population processes accounting for patterns of nucleotide sequence polymorphism.