Limited environmental stability of infectious porcine endogenous retrovirus type C; Usage of reverse transcriptase in combination with viral RNA as markers for infectious virus

INTRODUCTION: Porcine endogenous retroviruses (PERVs) are an integral part of the pig genome with infectious potential, as shown in vitro. HYPOTHESIS/GAP STATEMENT: In view of nonclinical and clinical xenotransplantation, data are essential that give an insight into viral pathogenicity. This includes PERV's environmental stability and environmental risk.AIM: We analyzed two ecotropic PERV-C (PERV-C[1312] and -[5683]), monitoring cell-free culture supernatants of infected ST-IOWA cells at various time intervals at room temperature (22°C +/−1°C). The virus was stored in the presence or absence of sterile wood litter, as used for large animal husbandry. This approach was set to determine the environmental stability of exogenous PERV-C at defined conditions for the first time. METHODOLOGY: Reverse transcriptase (RT) activity and viral RNA were monitored for up to 57 days and remaining infectivity of supernatant without wood litter was tested from day 7 onwards on naïve ST-IOWA cells. RESULTS: Results show that viral RNA decreases but remains detectable over the whole observation period, whereas RT activity showed 83%–96% reduction from day 7 on. This effect was stronger in the presence of wood litter and fresh harvested virus was more stable than frozen virus stocks. Even under these optimal conditions, no infectivity was shown for viral RNA-positive and RT-reduced supernatant harvested at day 7. CONCLUSION: The results confirm that PERV-C is less stable and the reduction of RT activity is accompanied by reduced infectivity, independently of existing viral RNA. The combination of both RT and viral RNA measurement is a suitable method to differentiate infectious PERV-C.