NUCLEIC-ACID STAINS AS INDICATORS OF CRYPTOSPORIDIUM-PARVUM OOCYST VIABILITY

We developed nucleic acid dye staining methodology for untreated, heat -treated and chemically inactivated C. parvum oocysts. The nucleic aci d staining was compared to in vitro excystation and animal infectivity using split samples of oocysts. Among the nucleic acid stains tested, SYTO(R)-9, hexidium and SYTO(R)-59 stained the oocysts consistently, and the staining was related to the infectivity of the oocysts to neon atal CD-1 mice but not to in vitro excystation. The nucleic acid viabi lity assay was used to determine log-inactivations of the oocysts afte r treatment with ozone, chlorine, chlorine dioxide and combinations of different chemical disinfectants, and was found to indicate log-inact ivation levels similar to that of animal infectivity. A combined immun ofluorescence-nucleic acid staining assay was developed for the oocyst s of C. parvum and this assay will be invaluable for the detection and viability of oocysts in the laboratory and in environmental samples. (C) 1997 Australian Society for Parasitology. Published by Elsevier Sc ience Ltd.