Effect of Porcine Epidemic Diarrhea Virus Infectious Doses on Infection Outcomes in Naïve Conventional Neonatal and Weaned Pigs

Thomas, Joseph T.; Chen, Qi; Gauger, Phillip C.; Giménez-Lirola, Luis G.; Sinha, Avanti; Harmon, Karen M.; Madson, Darin M.; Burrough, Eric R.; Magstadt, Drew R.; Salzbrenner, Holly M.; Welch, Michael W.; Yoon, Kyoung-Jin; Zimmerman, Jeffrey J.; Zhang, Jianqiang

A PEDV virus stock (USA/IN19338/2013 passage 7) with a known infectious titer of 5.62×10 5 TCID50/ml was 10-fold serially diluted into virus-negative cell culture medium, giving rise to theoretical infectious titers of 5.62×10 5 to 5.62×10 −5 TCID 50 /ml for the 10 0 to 10 −10 dilutions, respectively (Table 1) . Infectious titers of each virus dilution were back-titrated in Vero cells by end-point titration assay (TCID 50 /ml) and plaque assay (PFU/ml), with results summarized in Table 1 . The stock virus and 10 −1 to 10 −4 dilutions all had the same logarithms of titers as the theoretical titers based on the dilution factor, regardless of titration assays in the units of TCID 50 /ml or PFU/ml. The 10 −5 virus dilution had an infectious titer of 5 PFU/ml but remained undetected by the end-point titration assay in the unit of TCID 50 /ml. The 10 −6 to 10 −10 virus dilutions were undetected by either the end-point titration assay or the plaque assay during back titration.