EFFECT OF GAMMA IRRADIATION ON VIABILITY AND INFECTIVITY OF Cryptosporidium sp. OOCYSTS IN MUNICIPAL WASTEWATER EFFLUENT

Background: Cryptosporidiosis is still a public health problem worldwide. The transmissive stage (oocysts) occurs frequently in surface waters. The small size of oocysts (4-6 µm) and low infectious dose facilitate waterborne disease transmission.

Objectives: To examine the effects of gamma irradiation on permeability of the oocyst wall to vital dyes and in vitro excystation.

Materials and Methods: The ability of Cryptosporidium sp. oocysts to excyst and inclusion/exlusion of fluorogenic dyes DAPI, PI and nucleic acid stain SYTO-59 were examined after gamma irradiation at various doses (0,1,5,10,15 and 20 kGy). The assays were repeated ten days after the irradiation for post irradiation effects.

Results: The oocysts exposed to 10 kGy were not viable. At 10 kGy the gamma irradiated oocysts were still capable to excyst, however, after ten days they had completely lost the ability to excyst.

Conclusion: 10 kGy or higher doses of ionizing irradiation prevent the ability of Cryptosporidium oocysts to excyst and make the contained sporozoites nonviable.