Discovery and characterization of mammalian endogenous parvoviruses.

Public databases of nucleotide sequences contain exponentially increasing amounts of sequence data from mammalian genomes. Through the use of large-scale bioinformatic screening for sequences homologous to exogenous mammalian viruses, we found several sequences related to human and animal parvoviruses (PVs) in the Parvovirus and Dependovirus genera within genomes of several mammals, including rats, wallabies, opossums, guinea pigs, hedgehogs, African elephants, and European rabbits. However, phylogenetic analysis of these endogenous parvovirus (EnPV) sequences demonstrated substantial genetic divergence from exogenous mammalian PVs characterized to date. Entire nonstructural and capsid gene sequences of a novel EnPV were amplified and genetically characterized from rat (Rattus norvegicus) genomic DNA. Rat EnPV sequences were most closely related to members of the genus Parvovirus, with >70% and 65% amino acid identities to nonstructural and capsid proteins of canine parvovirus, respectively. Integration of EnPV into chromosome 5 of rats was confirmed by PCR cloning and sequence analysis of the viral and chromosomal junctions. Using inverse PCR, we determined that the rat genome contains a single copy of rat EnPV. Considering mammalian phylogeny, we estimate that EnPV integrated into the rat genome less than 30 million years ago. Comparative phylogenetic analysis done using all known representative exogenous parvovirus (ExPV) and EnPV sequences showed two major genetic groups of EnPVs, one genetically more similar to genus Parvovirus and the other genetically more similar to the genus Dependovirus. The full extent of the genetic diversity of parvoviruses that have undergone endogenization during evolution of mammals and other vertebrates will be recognized only once complete genomic sequences from a wider range of classes, orders, and species of animals become available.