Drying of Cryptosporidium oocysts and Giardia cysts to slides abrogates use of vital dyes for viability staining.

Vital dye staining has long been used to assess viability of Cryptosporidium oocysts and Giardia cysts, with staining and enumeration in suspension. Some recent studies, however, have dried samples to microscope slides prior to staining. Here we demonstrate that this approach may considerably underestimate parasite viability in the original sample.