Identification of a novel type C porcine endogenous retrovirus: evidence that copy number of endogenous retroviruses increases during host inbreeding

Different classes of porcine endogenous retroviruses (PERVs), which have the potential to infect humans during xenotransplantation, have been isolated from the pig genome. Because vertebrate genomes may contain numerous endogenous retrovirus sequences, the pig genome was examined for additional endogenous retroviruses, resulting in the isolation of a novel, complete endogenous retrovirus genome, designated PERV-E. The gag, pol and env genes of PERV-E are closely related to those of human endogenous retrovirus (HERV) 4-1, which belongs to the HERV-E family. Results of studies to determine the presence and copy number of PERVs demonstrated that PERV-E and PERV-A/B-like proviruses were present in all genomes tested, but that PERV-C was not found in two of the species examined, including wild boar. Multiple copies of PERVs could be found in each pig genome. Among all of the pig genomes tested, the wild boar genome had the lowest copy number of all PERVs, suggesting that the number of integrations of complete endogenous retroviruses is increased by inbreeding.