Oocyst age and excystation of Cryptosporidium parvum

Abstract

The effects of temperature, tap water, and excysting fluid were tested on oocysts of Cryptosporidium parvum that had been stored for 14, 32, or 43 weeks at 4 °C. In preparations containing 14-week-old oocysts, sporozoites excysted in the presence of excysting fluid at 37 °C, but did not excyst in excysting fluid at 22 °C nor in tap water at 22 or 37 °C. In contrast, numerous empty oocysts but few or no sporozoites were present in preparations of 32- or 43-week-old oocysts incubated in excysting fluid or tap water at 22 or 37 °C. Sporozoites in tap water lysed soon after leaving the oocyst. Thus, sporozoites of C. parvum will excyst from young oocysts only in the presence of excysting fluid at 37 °C, whereas older oocysts deteriorate with an increase in age and apparently become susceptible to the harmful effects of a hypotonic environment.