First evidence of previously undescribed trichomonad species in the intestine of pigs?

Abstract

Three different parasites of the phylum Parabasala (Tritrichomonas foetus, Trichomitus rotunda and Tetratrichomonas buttreyi) have been described in pigs. In a previous study (Mostegl et al., 2011) approximately 47% of 91 paraffin wax-embedded intestinal samples of pigs which were Trichomonas-positive by in situ hybridization using a probe with a broad reactivity spectrum contained other species than T. foetus. Out of these, intestinal trichomonads from three pigs (pigs 1-3) were further analyzed by gene sequencing of a part of the 18S ribosomal RNA (rRNA) gene using primer walking. Subsequently, the partial sequences achieved by the different primer pairs were combined to a sequence of about 1000 bp for each trichomonad. In all three pigs unique sequences were acquired which showed only moderate similarities to sequences available in the GenBank. Alignments and the BLAST analysis showed a high degree of homology between sequences of trichomonads from pig 1 and pig 3 with only 1% difference. These sequences were found to be 92% similar to Hypotrichomonas acosta, a trichomonad isolated from squamate reptiles. The trichomonad sequence detected in the intestine of pig 2 showed about 10% nucleotide differences compared to pigs 1 and 3. This sequence was 97% similar to two Trichomitus batrachorum (a frog symbiont) sequences. A phylogenetic analysis using the neighbor-joining and maximum likelihood methods supported the data of the BLAST analysis. These results suggest the presence of at least two as yet undescribed trichomonad species in the intestinal contents of pigs.