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

After 1 day acclimation (piglets were 6 days old), pigs in groups 1-7 were orogastrically inoculated with 10 −3 , 10 −4 , 10 −5 , 10 −6 , 10 −7 , and 10 −8 dilutions of the PEDV stock and the virus-negative cell culture media, respectively, using a size 8 French feeding tube and 60ml syringe (10ml/pig) ( Table 2 ). Piglets were evaluated daily for clinical signs of vomiting, diarrhea, lethargy, and body condition. Diarrhea severity was assessed with the following criteria by both visual observation and rectal swabbing: 'normal' = no diarrhea, 'mild diarrhea' = soft (cowpie), 'moderate diarrhea' = liquid with some solid content, 'watery diarrhea' = watery with no solid content. Rectal swabs were collected daily from each pig from 0 day post inoculation (DPI) until necropsy and were submerged into 1ml phosphate buffered saline (PBS, 1× pH 7.4) immediately after collection. Serum was collected before inoculation and at necropsy. Duration of the study was designed to be 0-7 DPI. However, per IACUC protocol, pigs with severe clinical signs were euthanized and necropsied at 4 DPI and the remaining pigs were kept through 7 DPI for necropsy (Table 3) . At necropsy, intestinal tissues and contents were grossly evaluated. Fresh proximal jejunum, middle jejunum, distal jejunum, ileum, cecum and colon were collected, along with cecum content. Additionally, a portion of the three sections of jejunum, and ileum were fixed in 10% neutral buffered formalin. Rectal swabs and cecum contents were tested by aforementioned quantitative PEDV N gene-based rRT-PCR. Formalin-fixed jejunum and ileum were submitted to the ISU VDL for histopathology and immunohistochemistry examinations.