Four adult female worms of Trichuris were isolated from an individual of the wild blue sheep (Pseudois nayaur) inhabiting the Helan Mountains, China, during an epidemiological survey of this wild ruminant. Although there were some differences among the worms in posterior end (rectum) morphology and egg shape, little information regarding species status could be inferred from their morphology. Phylogenetic trees were constructed based on sequences of the ITS1 segment of ribosomal RNA (rRNA), and the sequences of the four Trichuris specimens from wild blue sheep were divided into two distinct lineages (Clade A and Clade B). The two specimens in Clade A were named Genotype I, and had the closest relationship with Trichuris skrjabini; the two specimens in Clade B were named Genotype II and had the closest genetic relationship with a previously described Trichuris sp. In the two Trichuris genotypes identified in the present study, the 18S fragments (261 to 262 bp) of the newly obtained sequences were found to be highly conserved, with merely one insert mutation of a single nucleotide present. The genetic distance based on ITS1 between members of Clade A, composed of two T. skrjabini individuals and two Genotype I individuals, ranged from 0 to 0.0034. These distances are within the intraspecies variation of Trichuris (0-0.0272), suggesting that the Genotype I individuals infesting the wild blue sheep were T. skrjabini. In Clade B, the newly obtained sequences clustered with Trichuris sp. specimens isolated from ruminants (sheep and black goat) with strong support, and the genetic distance ranged from 0.0068 to 0.017, which is also within the intraspecies variation of Trichuris (0-0.0272). However, the genetic distances between the Clade A and Clade B were 0.0442 to 0.0578, which are higher than the intraspecies distances in Trichuris but lower than the interspecies distances (0.102-0.5078). These results implied that Clade A and Clade B most likely represent two subpopulations of T. skrjabini; however, the possibility that Clade A is T. skrjabini and Clade B is a Candidatus Trichuris could not be excluded.
Keywords: Blue sheep; Molecular phylogeny; Morphology; Trichuris.