• Cause: infection with Trichomonas gallinae. Trichomonas gallinae is a flagellated protozoan parasite with a direct lifecycle. Reproduction is by binary fission and transmission is horizontal. It primarily affects the upper digestive tract and upper respiratory tract, however more virulent strains can spread to affect other parts of the body, eg lungs, heart, liver and pancreas.
• Signs: these are generally associated with the necrotic plaques found in the upper digestive tract and upper respiratory tract and include: weight loss/emaciation; weakness; listlessness; open mouth breathing. Visible lesions known as ‘canker’ can be found within the oral cavity, crop and/or esophagus.
• Diagnosis: a presumptive diagnosis can be made from the clinical signs and confirmed with microscopy of material from swabs or wet smears, PCR or histopathology.
• Treatment: Trichomonas gallinae has historically been treated with nitroimidazoles, ie metronidazole, carnidazole, dimetridazole, but their use is prohibited in food producing animals in the UK, EU and USA. The use of tetracyclines has been suggested as an alternative, however there is limited evidence of its efficacy.
• Prognosis: guarded even with nitroimidazole use.

• Commonly, yellow necrotic plaques are seen in the oral cavity.
• Birds become inappetent leading to weight loss and emaciation. They also become weak and listless.
• Lesions can obstruct the upper respiratory tract causing open mouth breathing.

• Birds can present in acute respiratory distress if the upper respiratory tract is obstructed by lesions.
• With more virulent strains, the course of the disease is rapid with death occurring within 8-14 days.

• Trichomonas gallinae is present in a variety of avian species worldwide.

• Trichomonas gallinae is present in a variety of avian species worldwide but especially columbiformes (pigeons and doves).
• Presenting to the veterinarian in practice, trichomonosis primarily affects pigeons, doves, birds of prey, domestic fowl, and birds in captive collections.
• Pigeons are often blamed for transmission of trichomoniasis to turkeys and chickens.

• Although there is a theoretical potential, there is no known health threat to people.

• The economic impact of the disease in turkeys and chickens is difficult to assess, although infections are occasionally reported.

• Transmission from wild birds to domestic poultry.

• Infection with the flagellated protozoal parasite Trichomonas gallinae.

General

• Exposure to Trichomonas gallinae.
• Trichomonas is usually an opportunistic pathogen colonizing areas of damaged nasal, oral, esophageal or crop mucosa although it can be primary.

Specific

• Exposure of backyard poultry is through contaminated drinking water and occasionally food.
• Nearly all pigeons are carriers of this organism and Trichomonas gallinae is widely present in wild birds.
• The virulence of Trichomonas varies widely, with some strains capable of causing mortality.
• At one time investigators considered trichomoniasis to be synonymous with blackhead disease. However, these investigators failed to consider that more than one parasite might produce lesions of similar appearance.

• The severity of infection varies depending on the strain of the parasite.
• Trichomonas gallinae reproduces by longitudinal binary fission.
• Motile trophozoite and nonmotile pseudocysts are described.
• Cysts, sexual stages, or vectors are not known.
• The parasites are shed in saliva leading to contamination of water and feed. Feco-oral contamination with the parasite is not seen.
• Contaminated water and occasionally food is the most likely source of infection for backyard poultry.
• The protozoa initially invade the upper respiratory, oral, esophageal and/or crop mucosa causing ulceration which allows it to enter the circulatory system. This can lead to disseminated disease in the lungs, heart, liver and pancreas.
• Clinical signs result from the plaque-like lesions in the oral cavity and upper digestive tract. Primarily these cause a reduction in appetite and lead to weight loss. They can also lead to dyspnea due to obstruction of the upper respiratory tract.

• The timecourse of the disease is dependent on the strain: systemic signs can be present as early as 4 days post-infection (dpi), oropharyngeal lesions within 5-6 dpi and death within 8-14 dpi with more virulent strains.
• Chronic and asymptomatic infections can occur.

• Trichomonas gallinae is present worldwide.
• Can become prevalent within a group following ingestion of water or, less frequently, food often shared with wild birds, especially columbiformes.

ℹ️Trichomonosis is an emerging infectious disease of wild finches in the UK and these could act as an additional source of the infection.

Refereed papers

• Recent references from PubMed and VetMedResource.
• Amin A et al (2014) Trichomonads in birds – a review. Parasitology 141 (6), 733-747 PubMed.

Other sources of information

• Gerhold R (2021) Parasitic Diseases. In: Backyard Poultry Medicine and Surgery. A Guide for Veterinary Practitioners. 2nd edn. Wiley-Blackwell, USA. pp 11-216.
• Beckstead R (2020) Miscellaneous and Sporadic Protozoal Infections. In: Diseases of Poultry. 14th edn. Eds: Swayne D E, Boulianne M, Logue C M et al. Wiley-Blackwell USA. pp 1231-1242.
• Jackson R (2019) Gastrointestinal Disorders. In: BSAVA Manual of Backyard Poultry Medicine and Surgery. BSAVA, UK. pp 178-204.

_{Reproduced with permission from Cheryl B Greenacre & Teresa Y Morishita: Backyard Poultry Medicine and Surgery. A Guide for Veterinary Practitioners. © 2021, and David E Swayne: Diseases of Poultry. © 2020, published by John Wiley & Sons.}