COMPARISON OF ASSAYS FOR CRYPTOSPORIDIUM-PARVUM OOCYSTS VIABILITY AFTER CHEMICAL DISINFECTION

In vitro excystation, vital dyes (4', 6-diamidino-2-phenylindole (DAPI ) and propidium iodide (PI)), and infectivity in neonatal CD-1 mice we re used to assess the viability of Cryptosporidium parvum oocysts afte r chemical disinfection. In vitro excystation and DAPI/PI staining pro vided similar estimates of viability in bench-scale experiments, but b oth of these methods significantly overestimated the viability when co mpared with infectivity (Pr less than or equal to 0.01). Infectivity w as the most reliable measure of the viability of C. parvum oocysts fol lowing chemical disinfection.