Effect of the mixed-oxidant solution on infectivity of Cryptosporidium parvum oocysts in a neonatal mouse model

Abstract

Cryptosporidium parvum oocysts were exposed to the mixed-oxidant solution, which was electrochemically generated by Miox Water Disinfection Unit, and sodium hypochlorite in phosphate buffered saline (PBS, pH 7.2) or biologically treated wastewater at 25 degrees by using concentrations of residual chlorine of up to 5 mg/l and contact times of up to 8 h. The effect of two disinfectants on infectivity of the oocysts in a neonatal murine model was comparatively evaluated by determining the total number of oocysts recovered from the intestine. Exposure to the mixed-oxidant solution at 2 and 5 mg/l (residual chlorine) yielded a significant inactivation of infectivity in the dose- and exposure time-dependent manner, while exposure to 5 mg/l (residual chlorine) of sodium hypochlorite for contact times of up to 4 h produced no measurable inactivation of infectivity. Morphological examination also revealed a picture of degenerating oocysts after exposure to 5 mg/l (residual chlorine) of the mixed-oxidant solution, but not with sodium hypochlorite. When the oocysts were exposed to either biologically treated wastewater--or PBS-diluted the mixed-oxidant solution at 5 mg/l (residual chlorine) for 4 h, the disinfectants produced a significant inactivation of infectious oocysts. The decrease number of the oocysts was 0.8 log 10 in the former and 2.1 log 10 in the latter. These results demonstrate that the mixed-oxidant solution may be a useful disinfectant against Cryptosporidium oocysts, but appropriate applications need to be validated.