Factors that may influence the higher susceptibility of nursing
piglets to PEDV infection and slower recovery from disease
include the slower turnover of enterocytes in neonatal nursing
piglets (5–7 days) vs. weaned pigs (2–3 days) (Jung and Saif, 2015;
Moon et al., 1973). The proliferative level of intestinal crypt
cells determines the turnover time of enterocytes in pigs. The
turnover rate of the intestinal epithelium may also depend on
stem cells in the intestinal crypts. Intestinal stem cells consist
mainly of three cell types: leucine-rich repeat-containing
G protein-coupled receptor 5-positive crypt base columnar cells
(LGR5-positive crypt cells), +4 cells, and Paneth cells (Sato and
Clevers, 2013); however, the presence of Paneth cells in the
intestine of swine is debatable (Burkey et al., 2009). Intestinal
crypt stem cells may be critical for the epithelial cell renewal
during PEDV infection.