INFECTIVITY OF PRESERVED CRYPTOSPORIDIUM-PARVUM OOCYSTS FOR IMMUNOSUPPRESSED ADULT MICE

The present study was undertaken to determine the infectivity of Crypt osporidium parvum oocysts for immunosuppressed adult C57BL/6N mice aft er the oocysts had been stored from 1-48 months at 4 degrees C in 2.5% potassium dichromate. All mice inoculated with oocysts 1-18 months ol d developed patent infections, while mice inoculated with older oocyst s remained uninfected. The prepatent period was extended from 2 to 6 o r 7 days as the storage time for oocysts increased. The finding that C . parvum oocysts remain infective for mice for at least 18 months offe rs important economic and time-saving advantages for investigators who frequently require large numbers of oocysts that must be painstakingl y purified from calf manure.