Amoebic Cysticidal Properties of Halogens in Water

Amoebic cysts are evaluated for their comparative sensitivities to aqueous solutions of iodine, free chlorine, inorganic chlorine, and N-Chloroglycine of varying concentrations and pH values. A mixture of amoebic cysts, consisting predominately of Entamoeba histolytica and Entamoeba coli, which are concentrated from the feces of naturally infected monkeys, are used in the study. These cysts are as resistant to the halogens as E. histolytica from a human carrier. That study reveals that the chemical species of free and combined halogens which prevail in the low pH waters are superior cysticides when compared to the forms which predominate in waters of high pH. The chemical species which predominate in waters of high pH are considerably less cysticidal. These forms are rated in the following order: Hypochlorite ion monochloramine hypoiodous acid. A new cyst bioassay system is developed which enables cyst survival to be expressed as a percentage of the total number of cysts in a sample.