[The efficacy of water ozonation on the inactivation of oocysts of Cryptosporidium]

Abstract

Cryptosporidium oocysts are currently found in surface waters. Their incomplete removal by sand filtration and their high resistance to chlorinated disinfectants make possible waterborne cryptosporidiosis outbreaks after drinking treated water. Because ozone is an alternative to chlorine for final drinking water disinfection the aim of our study was to determine the ozonation conditions able to eliminate the infectivity of oocysts. Feces from horses naturally infected by C. parvum were mixed with distilled water. The obtained suspension was clarified by passing through a graded series of four sieves (pore sizes, 315, 200, 125 and 63 microns). The clarified suspension was decontaminated by adding a 10% sodium hypochlorite solution. After a 10 minute contact time at room temperature, the chlorine residual was neutralised by the exactly requisite volume of a 0.01 N sodium thiosulfate solution. Oocysts in the suspension were purified by centrifugation and washing of pellets in distilled water. Oocysts in the finally obtained suspension were numerated by counting in a Malassez haemocytometer. Ozonated water containing dissolved ozone residuals ranging from 0.44 mg/l to 1.09 mg/l were inoculated with a number of oocysts ranging from 1.10(6) to 1.10(8). Contact times with ozone were 4.6 or 8 minutes. After destroying the ozone residual by sodium thiosulfate, ozonated oocysts were administered by oral route to male Sprague-Dawley rats weighing between 180 to 200 g and beforehand immunosuppressed by a regimen of 25 mg hydrocortisone acetate subcutaneously twice a week, 5 weeks before and 3 weeks after Cryptosporidium challenge. Oocyst shedding was daily controlled by phase contrast microscoy in smears of fecal suspension mixed with carbolfuchsine solution.(ABSTRACT TRUNCATED AT 250 WORDS)