Trichomonas stableri n. sp., an agent of trichomonosis in Pacific Coast band-tailed pigeons (Patagioenas fasciata monilis)

Abstract

Trichomonas gallinae is a ubiquitous flagellated protozoan parasite, and the most common etiologic agent of epidemic trichomonosis in columbid and passerine species. In this study, free-ranging Pacific Coast band-tailed pigeons (Patagioenas fasciata monilis) in California (USA) were found to be infected with trichomonad protozoa that were genetically and morphologically distinct from T. gallinae. In microscopic analysis, protozoa were significantly smaller in length and width than T. gallinae and were bimodal in morphology. Phylogenetic analysis of the ITS1/5.8S/ITS2, rpb1, and hydrogenosomal Fe-hydrogenase regions revealed that the protozoan shares an ancestor with Trichomonas vaginalis, the sexually-transmitted agent of trichomoniasis in humans. Clinical and pathologic features of infected birds were similar to infections with T. gallinae. Evidence presented here strongly support taxonomical distinction of this parasite, which we hereby name Trichomonas stableri n. sp. This work contributes to a growing body of evidence that T. gallinae is not the sole etiologic agent of avian trichomonosis, and that the incorporation of molecular tools is critical in the investigation of infectious causes of mortality in birds.

Keywords: Avian trichomonosis; Band-tailed pigeon; Columbidae; Fe-hydrogenase; ITS1/5.8S/ITS2; Phylogeny; Trichomonas gallinae; rpb1.

Graphical abstract

Fig. 1

Micrographs of T. gallinae and T. stableri trophozoites. (A) T. gallinae, illustrating the four anterior flagella, and the extension of the axostyle. Note the slender appearance of the trophozoite with a near elliptical form. (B) Slender form of T. stableri is shown with protruding axostyle and four anterior flagella. (C) Rounded form of T. stableri is shown with the four anterior flagella. All scale bars are 5 μm.

Fig. 2

Consensus phylogenetic tree of ITS1/5.8S/ITS2 sequences (260 bp alignment) made by Bayesian inference. Legend denotes substitutions per site. All posterior probabilities are >90% unless otherwise noted. ITS region Sequence Groups refer to designations described in Gerhold et al. (2008). BTPI, band-tailed pigeon; BWHA, broad-winged hawk; COHA, Cooper’s hawk; ECDO, Eurasian collared dove, GRDO, common ground dove; HOFI, house finch; MODO, mourning dove; ROPI, rock pigeon; WWDO, white-winged dove.

Fig. 3

Consensus phylogenetic tree of partial Fe-hydrogenase gene sequences (750 bp alignment) made by Bayesian inference. Legend denotes substitutions per site. All node posterior probabilities are >90% unless otherwise noted.

Fig. 4

Consensus phylogenetic tree of partial rpb1gene sequences (1191 bp alignment) made by Bayesian inference. Legend denotes substitutions per site. All node posterior probabilities are 100% unless otherwise noted.

Fig. 5

Pathogenesis of T. stableri in Pacific Coast band-tailed pigeons. Oral and esophageal caseonecrotic lesions (e.g., white arrowheads) observed during post-mortem examination in cases CA015500 (A) and CA015499 (B). Both birds were collected and sampled between February 16 and February 19, 2012 during a trichomonosis mortality event in Monterey County, California. Infection with T. stableri was confirmed by DNA amplification performed directly on lesion tissues. (C) Immunohistochemical staining of trichomonad antigen (red) in lung tissue of case CA015506. Lung infection likely occurred via aspiration of necrotic debris from the laryngeal region. Scale bar is 50 μm. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 6

Geographic distribution of birds (solid black circles) infected with T. stableri in California. Circle size is relative to the number of birds infected at each site.