Viable Cryptosporidium parvum oocysts exposed to chlorine or other oxidising conditions may lack identifying epitopes.

The intestinal protozoan parasite Cryptosporidium parvum is a known cause of water-borne disease in humans. The detection of Cryptosporidium oocysts in water samples relies upon the use of fluorescently labelled antibodies, preferably using flow cytometry and epifluorescence microscopy. Here we demonstrate that four commercially available antibodies recognise a similar set of immunodominant epitopes on the oocyst wall. These epitopes appear to be carbohydrate in nature and are labile to chlorine treatment and oxidising conditions. Sodium hypochlorite and sodium meta-periodate reduced the ability of the antibodies to detect Cryptosporidium oocysts. Damage to the epitopes did not necessarily reduce the viability of oocysts. This finding may be important for the water industry, where naturally occurring oxidising conditions or sanitizing treatments could produce viable oocysts that are undetectable using standard protocols.