Endogenous retroviruses are present in all bird and mammalian species including the pig. In humans most are benign but some are thought to be associated with genetic, autoimmune, and other disease syndromes. In the pig three categories of endogenous retroviruses exist. These are designated as Porcine Endogenous Retrovirus A, B, & C. (PERV-A, B, & C). Exogenous retroviruses are infectious and have the ability to become a part of the host species genome by incorporating their genetic code into the genetic code of the host. The endogenous retroviruses are believed to be remnants once infectious or exogenous retroviruses that over many years and generations loose infectiousness and the ability to replicate in the host. There are no known exogenous retroviruses in pigs. In recent years pig PERV’s have been extensively studied out of interest to use the pig as a potential xenotransplant organ donor for humans. When certain pig cell culture lines are in direct contact with human cell culture lines, porcine endogenous retroviruses have the ability to infect the human cells. This raised fears that if pig organs were used in immune suppressed humans the pig viruses could jump species and become infectious and contagious in the human recipient and contact persons. PERV-A and a recombinant PERV-A/C which appears to regain the ability to replicate were infectious in the cell culture studies. Although these viruses have been extensively investigated in human xenotransplant studies, these endogenous viruses have not been examined as a potential health risk for the commercial pig. All pigs carry PERV-A and PERV-B in their genome but only a limited number are also carriers of the PERV-C. If it could be determined that the PERV-A/C acts in association with other agents leading to greater pathogenesis, the developed RT-PCR assays from this study could be used to eliminate the PERV-C from the gene pool since it is only present in a relatively small percentage of pigs.
The goal of this study was to develop several real-time RT-PCR assays capable to detection PERV-ABC, PERV-C and recombinant PERV-A/C. Once test capabilities were developed the further goal was to establish the level of PERV-C in commercial pigs in Iowa and the U.S. in a cross-sectional study. The final goal was to investigate the presence of PERV-A/C and determine any association with apparent disease. Once the assays were developed and validated, we surveyed several hundred commercial pigs of different ages and different sites to determine the relative levels of the three classes of PERV. As in other published reports, all the study pigs were positive to PERV-A and PERV-B. Only 24% of those sampled were positive to PERV-C while 18% were also positive to the PERV-A/C.
The spontaneous recombination of PERV-A and PERV-C is thought to be associated with immune stimulation. To evaluate the pathogenic role of PERV-A/C in pigs suffering from disease outbreak situations, sites were identified and paired samples from affected and non-affected pigs were collected. Disease outbreaks associated with several agents were identified and paired samples were collected for assay. This final component of the study is still underway as we continue to identify disease outbreaks in various parts of the U.S. A second paper will be submitted for publication once the final analysis is completed.
