Cryptosporidium parvum oocysts recovered from water by the membrane filter dissolution method retain their infectivity

Cryptosporidium parvum oocysts infectious to neonatal BALB/c mice were processed by the cellulose acetate membrane (CAM) filter dissolution method to determine if the procedure that utilizes acetone incubation and alcohol centrifugations alters their viability (determined by in vitro excystation) or infectivity (determined by infectivity bioassay). In addition, most oocysts with altered viability by desiccation, heat inactivation, and snap freezing that were processed by the CAM filter dissolution method were nonrefractile, unstained oocyst ghosts. The remaining organisms, oocyst shells, were lightly stained with the acid-fast stain. Infectious oocysts retained their infectivity and nonviable oocysts (oocyst shells) retained their morphology when processed by the CAM dissolution method. Infectious oocysts, oocyst shells, and oocyst ghosts produced positive reactions of similar intensity in direct immunofluorescence antibody staining, utilizing the MERIFLUOR(TM) Cryptosporidium/Giardia test kit. Crystosporidium oocysts recovered from finished drinking water by the CAM dissolution method can be subjected to testing for their viability and infectivity.