Abstract
Although pretreatment with acidified HBSS has been used to determine the viability of Cryptosporidium parvum oocysts via in-vitro excystation and/or DAPI/PI permeability assay, little information is available on the effect of pretreatment on viability. In this study, we evaluated the effect of different periods of incubation at 37°C in acidified HBSS on the viability of fresh oocysts and UV-irradiated oocysts, using both excystation assay and DAPI/PI permeability assay. The effect of incubation time on the viability of oocysts differed not only between the two assays but also between the fresh oocysts and the UV-irradiated oocysts. Appropriate preincubation time common to both fresh oocysts and UV-irradiated oocysts for maximal viability was 5 min in the excystation assay. In contrast, preincubation was found to reduce viability in the DAPI/PI permeability assay, and is therefore not recommended for this assay.
