On the identification of some Entamoeba species. Comments on a recent paper

Trophozoites and four-nucleated cysts of E. equi were described by Fantham (1921) from two horses with intestinal disturbance. No cysts were found in the horse stool sample analysed by Clark et al. (2006) and there is no description of the trophozoites found in culture [the paper they refer to (Clark & Diamond, 2002) is only a revision of culture methods]. It is impossible to confirm whether or not these trophozoites are compatible with Fantham’s description or whether they really form four-nucleated cysts. Furthermore, despite environmental contamination being detected in the sample (Colpodella spp. were also found), the authors did not explain why this possibility was not taken into consideration for the Entamoeba trophozoites (especially when no cysts were found in the sample). In our opinion, the only valid identification that applies is Entamoeba sp., and the genetic characterization and validation of E. equi should wait until new isolates are obtained.