Infectivity of Giardia sp. cysts in relation to eosin exclusion and excystation in vitro.

The aim of the investigation was to determine the relationship between eosin exclusion, in vitro excystation and experimental infection, as determinants of Giardia sp. cyst viability. The results of experiments clearly show that the excystation induced in vitro, being a more sensitive indicator of cyst viability than is eosin exclusion, is, at the same time, technically more complicated and gives in some cases different and subjective results which are affected by the technique itself. The results of objective experimental infection of rats showed that there is no relation between percentage excystation in vitro, eosin exclusion and cyst infectivity. One may assume that in vitro excystation methods are not always objective determinants of Giardia cysts viability. However, the high excystation rate obtained exceptionally by Schaefer and co-workers showed the possibility for elaboration of an objective excystation procedure in vitro as a simple method for Giardia cyst viability determination.