Novel insights into the genetic diversity of Balantidium and Balantidium-like cyst-forming ciliates

Abstract

Balantidiasis is considered a neglected zoonotic disease with pigs serving as reservoir hosts. However, Balantidium coli has been recorded in many other mammalian species, including primates. Here, we evaluated the genetic diversity of B. coli in non-human primates using two gene markers (SSrDNA and ITS1-5.8SDNA-ITS2). We analyzed 49 isolates of ciliates from fecal samples originating from 11 species of captive and wild primates, domestic pigs and wild boar. The phylogenetic trees were computed using Bayesian inference and Maximum likelihood. Balantidium entozoon from edible frog and Buxtonella sulcata from cattle were included in the analyses as the closest relatives of B. coli, as well as reference sequences of vestibuliferids. The SSrDNA tree showed the same phylogenetic diversification of B. coli at genus level as the tree constructed based on the ITS region. Based on the polymorphism of SSrDNA sequences, the type species of the genus, namely B. entozoon, appeared to be phylogenetically distinct from B. coli. Thus, we propose a new genus Neobalantidium for the homeothermic clade. Moreover, several isolates from both captive and wild primates (excluding great apes) clustered with B. sulcata with high support, suggesting the existence of a new species within this genus. The cysts of Buxtonella and Neobalantidium are morphologically indistinguishable and the presence of Buxtonella-like ciliates in primates opens the question about possible occurrence of these pathogens in humans.

Figure 1. SSrDNA tree based on Trichostomatia SSrDNA sequences computed by RAxML.

A. The numbers above the branches represent Maximum likelihood bootstrap supports as computed from 1000 replicates. The scale bar represents 10 changes per 100 positions. B–E. The tree is complemented by an AU topology test, with all tested topologies shown below the main tree (topologies shown in reduced form). New sequences are marked with a star.

Figure 2. Maximum likelihood phylogenetic tree as inferred from the ITS1-5.8S-ITS2 DNA region.

The tree was computed using PhyML with the GTR model for nucleotide substitutions. Numbers above branches indicate ML bootstrap support from 1000 replicates/PhyloBayes posterior probabilities computed with CAT model/PhyloBayes posterior probabilities computed with GTR model. New sequences are marked with a star.

Figure 3. Reproduction of the original drawings of trophozoites of Paramecium coli, Balantidium entozoon and Buxtonella sulcata.

A. P. coli from Malmstein (1857); B. B. entozoon from Claparéde & Lachmann (1858); and C. B. sulcata from Jameson (1926).

Figure 4. A–D: Comparison of cysts of Neobalantidium coli, Buxtonella sulcata and a Buxtonella-like ciliate; scale bars = 10 µm.

A. Cyst of N. coli from a domestic pig with visible ingested starch grains inside. B, D. Cysts of Buxtonella-like ciliate from an agile mangabey showing the trophozoite with visible rows of cilia (B, arrowhead). C. Cyst of B. sulcata from cattle with visible macronucleus (arrowhead). E. Trophozoite of Buxtonella sulcata with typical sulcus (arrowhead); scale bar = 20 µm. F. Detail of sulcus of Buxtonella sulcata (arrowhead); scale bar = 5 µm.