PED is the most devastating in nursing piglets (under
3-weeks-old), causing 100% morbidity and 50–100% mortality
(Saif et al., 2012; Stevenson et al., 2013). In specific-pathogen-free
(SPF) pigs from 2 days to 12 weeks of age, experimentally
inoculated with a wild-type Japanese PEDV strain, deaths occurred
mainly in 2- to 7-day-old pigs and virus replication was higher in
newborn pigs (Shibata et al., 2000). Conventional 3-week-old
weaned pigs experimentally inoculated with a US PEDV strain exhibited relatively milder clinical disease (Madson et al., 2014).
However, the mechanisms by which PEDV infection induces
greater disease severity and deaths of nursing piglets vs. weaned
pigs, have not been clearly defined (Jung and Saif, 2015).