THE EFFECT OF OZONE ON THE VIABILITY OF CRYPTOSPORIDIUM-PARVUM OOCYSTS AND A COMPARISON OF EXPERIMENTAL METHODS

Cryptosporidium parvum oocysts were exposed to ozone using two experim ental systems. The first method involved producing residual concentrat ions of 1, 3 and 5 mg/L of ozone in 500 ml of water in a Drechsel gas bottle, which was then inoculated with oocysts. The second method invo lved inoculating 7 L of water with oocysts and then applying a constan t dose of 1, 3 and 5 mg/L of ozone, circulating the water in a contact or system. Viability was assessed by the inclusion/exclusion of fluoro genic vital dyes. Comparison of these two methods showed that the seco nd method was considerably more successful at reducing oocyst viabilit y than the first method. Experiments performed at an increased tempera ture using method one indicated that temperature was an influencing fa ctor on oocyst inactivation by ozone treatment.