Forty-two Trichomonas gallinae isolates were molecularly characterized to determine whether isolates differed in genetic sequence of multiple gene targets depending on host species or geographical location. The 5.8S ribosomal RNA (rRNA) and flanking internal transcribed spacer (ITS) gene regions were amplified by polymerase chain reaction, and the sequences were analyzed phylogenetically. The results of the sequence analysis strongly suggest at least 2 species may exist within the T. gallinae morphologic complex. Based on ITS sequences, one group demonstrated high nucleotide identity to the 3 T. gallinae sequences available in GenBank, whereas the second group was more closely related to T. vaginalis (98%) than to T. gallinae (92%). Two common ground-dove (Columbina passerina) isolates shared a 95% identity with T. vaginalis and a 92% identity with T. gallinae and T. tenax. Sequence analysis of both the 18S rRNA and α-tubulin genes from a subset of the isolates supports the 5.8S-ITS sequence results. All of the T. vaginalis-like isolates originated from Arizona, California, or Texas, whereas T. gallinae isolates were found in all sampled states. Both T. vaginalis-like and T. gallinae isolates were involved in trichomoniasis outbreaks in California and Arizona.

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