Approximately one plaque-forming unit (PFU) of the highly virulent PEDV PC22A strain (at passage level 3) caused watery diarrhea in 40% of 4-dayold CDCD piglets within 24 HPI . Similarly, the minimal infectious dose of another highly virulent US PEDV strain USA/IN19338/2013 was titrated as 0.056-0.56 TCID 50 in 5-dayold conventional piglets and 56 TCID 50 in 21-day-old conventional weaned pigs, respectively (Thomas et al., 2015) .