Comparison of assays for<i>Cryptosporidium parvum</i>oocysts viability after chemical disinfection

Abstract

In vitro excystation, vital dyes (4', 6-diamidino-2-phenylindole (DAPI) and propidium iodide (PI), and infectivity in neonatal CD-1 mice were used to assess the viability of Cryptosporidium parvum oocysts after chemical disinfection. In vitro excystation and DAPI/PI staining provided similar estimates of viability in bench-scale experiments, but both of these methods significantly overestimated the viability when compared with infectivity (Pr < or = 0.01). Infectivity was the most reliable measure of the viability of C. parvum oocysts following chemical disinfection.