Inactivation of Cryptosporidium spp. oocysts with ozone and ultraviolet irradiation evaluated by in vitro excystation and animal infectivity

Abstract

Cryptosporidium parvum and Cryptosporidium muris oocysts were exposed to ozone and/or ultraviolet(UV) lamp in bench-scale batch reactors. The effect of ozone, UV, and sequential disinfection method on two kinds of oocysts were determined with in vitro excystation and animal infectivity test. The results of ozone exposure experiments showed that the required Ct values were about 3 and 8 mg · min./L for 2-log and 3-log reduction ininfectivity of C. parvum oocysts at room temperature, respectively. But larger values of Ct were needed at low temperature. In the case of sequential disinfection methods with ozone and UV, more than 1-log reduction in infectivity was achieved with 15 sec. of UV irradiation. There was no significant correlation between the excystation ratios and the reduction ratios in infectivity. Moreover, the results of dose-response of animal infectivity test indicated the possibility of a new method to evaluate the infectivity of Cryptosporidium parvum oocysts.