Gross Findings: 

On external examination, a large number of wheat seeds are present in the oral cavity (Fig. 1A).  Claws and distal phalanges are absent on both feet (see October 2024 COM). On internal examination, there is no subcutaneous, visceral, or epicardial fat.  Pectoral muscle is severely atrophied.  The oropharynx is thickened by tan/yellow caseous material (Fig. 1B).  Multiple raised tan/yellow nodules are present in the proximal esophagus (Fig. 1B). The largest measures 7 mm in diameter by 5 mm.  The esophagus is empty.  The proventriculus is empty.  The ventriculus contains a small amount of green plant material.

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Disease: Trichomonosis, canker, roup; frounce in raptors

Etiology: Trichomonas gallinae, a flagellated, amitochondriate, microaerophilic, protozoan parasite 

Host range: The rock pigeon (Columba livia) is the primary host.  Infection occurs in columbiformes, falconiformes, strigiformes, passeriformes and charadriiformes.  Infections in captive birds or experimental hosts have occurred in psittaciformes, galliformes, gruiformes, and anseriformes. 

Distribution: Occurs on all continents except Antarctica; does not occur in Greenland and northern parts of North America, Europe, and Asia.

Pathogenesis: There are nonpathogenic, mildly pathogenic, moderately pathogenic, and virulent strains.  Avirulent strains may result in the absence of disease.  Mildly pathogenic strains may result in an excess of saliva and mild inflammatory lesions in the oral cavity and upper gastrointestinal tract, while more virulent strains cause caseous lesions in the oral cavity and throat and even in the sinuses, skull, and skin.  Some highly virulent strains can cause lesions in internal organs.  Death can occur within days.  Oral lesions can impair swallowing causing emaciation and eventual death.  If lesions block air flow in the trachea, respiratory failure can result in death.  If internal organs are invaded and fail, death can occur.

Transmission: Infected columbiform adults transmit the organism from the oral cavity and upper digestive tract to squabs when they regurgitate pigeon milk.  Transmission also can occur via cross-feeding or during courtship when bills come in contact.  Swallowing can become difficult in infected birds, and they can drop large, contaminated pieces of grain that they cannot swallow, which can then infect another bird that picks it up.  Birds infected with avirulent strains can drop infected grain under normal circumstances, and it can then be consumed by an uninfected bird.  Transmission can also occur via contaminated water. Infection in raptors occurs when they consume infected prey.

Life cycle: The life cycle is direct with no intermediate or paratenic hosts.

Clinical signs: Anorexia, weight loss, lethargy, ruffled feathers, swollen face, pendulous crop, excessive watery saliva, foul odor, increased thirst, dysphagia, dyspnea, nasal and oral exudation, diarrhea, and vomiting.

Gross findings: In the oral cavity, lesions are yellow, caseous, and well circumscribed.  Early in infections, oral lesions may be small and not raised.  As the disease progresses, lesions can develop raised projections and can coalesce to form large masses.

Histologic findings: In the oral cavity, there is ulceration and inflammation, with organisms observed at the periphery of necrotic lesions.

Diagnosis: History, clinical signs, gross and microscopic findings, wet-mount microscopy, culture, and PCR.

Wildlife population impacts: The disease often affects individuals or a group of nestlings, but large-scale epizootics can occur especially in columbiformes.

Management: Treatment of wild birds is not practical.  Cleaning bird feeders and water sources may reduce infections.

References:

• Amin A, Bilic I, Liebhart D, & Hess M. 014. Trichomonads in birds--a review. Parasitology 141(6): 733–747. DOI:10.1017/S0031182013002096
• Forrester DJ & Foster GW. 2008. Trichomonosis. In: Parasitic Diseases of Wild Birds. Atkinson CT, Thomas NJ, Hunter DB, editors. Wiley-Blackwell, Ames, Iowa, pp. 120–153.