INDUCTION OF FOLDS OR SUTURES ON THE WALLS OF CRYPTOSPORIDIUM-PARVUM OOCYSTS AND THEIR IMPORTANCE AS A DIAGNOSTIC FEATURE

The proportion of oocysts of Cryptosporidium parvum showing a fold on oocyst walls when incubated with either fluorescent monoclonal antibod y or a surface-reactive fluorescent dye was increased by incubating su spensions of oocysts with dimethyl sulfoxide, sucrose, or Hanks' balan ced salt solution. Further incubation of sucrose-incubated oocysts wit h water showed this to be a reversible phenomenon. Oocysts demonstrati ng this fold after incubation in dimethyl sulfoxide were of the same v iability as control oocysts and followed the same excystation dynamics . Despite this fold having been previously described as a suture, we w ere unable to find any evidence that this pattern of fluorescence high lighted the same suture that has been described in ultrastructural stu dies. Furthermore, oocysts were observed in which this fold was not al ways continuous with the gape in the oocyst wall through which the spo rozoites had emerged. We propose that this fluorescently highlighted r egion or fold should no longer be described as a suture and question i ts validity as a diagnostic feature. When environmental and other samp les are being examined for the presence of C parvum oocysts, objects o f appropriate size, shape, and fluorescence which do not demonstrate a surface fold should not necessarily be excluded.