Abstract
The infectious dose of a virus pool of original US PEDV strain PC22A was determined in 4-day-old, cesarean-derived, colostrum-deprived (CDCD) piglets. The median pig diarrhea dose (PDD50) of the virus pool was determined as 7.35 log10 PDD50/mL, similar to the cell culture infectious titer, 7.75 log10 plaque-forming units (PFU)/mL. 100 PDD50 caused watery diarrhea in all conventional suckling piglets (n = 12) derived from a PEDV-naive sow, whereas 1000 and 10 000 PDD50 did not cause diarrhea in piglets derived from two PEDV-field exposed-recovered sows. This information is important for future PEDV challenge studies and validation of PEDV vaccines.
Highlights
The infectious dose of a virus pool of original US Porcine epidemic diarrhea (PED) virus (PEDV) strain PC22A was determined in 4-day-old, cesarean-derived, colostrum-deprived (CDCD) piglets
In this study, we used CDCD pigs to determine the The median pig diarrhea dose (PDD50) of a PEDV virus pool for several reasons: 1) Random allocation of CDCD piglets into different groups eliminated the influence of litter-to-litter variation; and 2) to reduce the number of experimental animals required for the determination of PDD50, compared to using conventional suckling pigs in which at least one litter of pigs is required per group
After the PDD50 was determined in CDCD pigs, the results were confirmed in age-matched conventional pigs, suggesting CDCD piglets are a reliable and economic model to determine the PDD50 and virulence of a PEDV strain
Summary
4.9-5.5 f aEach pig was inoculated orally with 3 mL inoculum. bTiters were calculated based on the titer of the original virus pool and dilution times. cFecal scores of 3 as determined by 24 hpi for pigs in G1-G8 and control groups and conventional pigs of sow E, and through 7 and 9 dpi for conventional pigs of sows F and G, respectively. dNegative or below detection limit of RT-qPCR (4.8 log10GE/mL). eData of 10 pigs, which tested positive. fData of 2 pigs, which tested positive. gPiglets of control 1 group were housed in the same room as G5 piglets. To reduce the risk of cross contamination among pigs, PEDV PC22A-inoculated CDCD piglets were euthanized at onset of watery diarrhea and subjected to necropsy examination. Because conventional suckling pigs are the targets for future vaccine studies, PEDV-naïve sow E was selected and the naturally delivered suckling piglets were inoculated orally with PC22A at 100 PDD50/pig at 4 days of age to verify the results from the CDCD pig experiments. Serum samples of sows F and G tested positive for PEDV-specific IgG, IgA and virus neutralizing antibodies at 53 days post-outbreak (20 and 22 days pre-farrowing) (Table 2) by PEDV-specific cell culture immunofluorescence (CCIF) and plaque reduction virus neutralization (PRVN) assays as described [16]. Sows F and G delivered 13 and 10 piglets, respectively, by natural farrowing Piglets and their sows were housed together in separate rooms for each litter.
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