Tentative identification of the species of Balantidium from ostriches (Struthio camelus) as Balantidium coli-like by analysis of polymorphic DNA

The characteristics of Balantidium from ostriches (Struthio camelus) are similar to those of Balantidium coli; however, the species Balantidium struthionis was proposed on the basis of the host species (ostriches) and the shape of the macronucleus (with a deep depression in one side). In the present work, we have performed morphological and genetic comparisons between isolates of Balantidium from ostriches and B. coli from pigs to determine the specific status of B. struthionis. The morphological characteristics of the trophozoites of Balantidium from ostriches were reviewed in 100 trophozoites from two isolates. The macronucleus’ shape of the ostrich Balantidium was highly variable, thus the use of this criterion for diagnostic purposes is not reliable. Besides, very few trophozoites showed a deep depression in their macronucleus and almost all the trophozoites conform to the description of B. coli. The complete sequence of the DNA coding for the 18s-rRNA–ITS1–5.8s-rRNA–ITS2 regions were obtained by PCR from five pig and five ostrich isolates. The sequences corresponding to the 18s and 5.8s-rRNA genes were identical for the ostrich and pig isolates. Two clearly different genotypes were found in the analysis of the ITS1 and ITS2 regions of the pig isolates; the genotype A was identified in all isolates, while the genotype B was found in only two of them. Their sequences show clear differences from that published corresponding to a B. coli gorilla isolate, which we will consider as a different genotype, C. In our opinion, these different B. coli genotypes reflect the genetic variability of this organism, but further studies would be necessary to determine if it could have practical importance. The polymorphism of the ITS regions have been also found in the ostrich isolates. The same genotypes A and B have been identified, although not as mixed infections. The morphological characteristics and the genetic results suggest that the species name B. struthionis is a synonym of B. coli; however, until experimental infections are carried out to determine if the parasite is transmissible between pigs and ostriches, it would be preferable to tentatively designate it as B. coli-like.