2012; Zhang and Huang 2013). We detected a significant decrease in lgr5 and Sox9 RNA levels in enteroids following infection (Fig. 4A). By immunohistochemistry, we observed that the number of Lgr5‐positive cells declined in infected enteroids, compared with uninfected control enteroids (Fig. 4B). Moreover, decrease in the RNA levels of Lgr5 and Sox9 was further confirmed in ileum intestinal epithelium isolated from in vivo infected neonatal mice after oral gavage of C. parvum oocysts (Fig. 4C). This evidence concerns the gene SOX9 and infection.