Trichomonosis in birds is caused by flagellated protozoal parasites, leading to caseous necrosis of the oral cavity and potentially orbital, brain, and liver lesions. Diagnosis is suggested by gross lesions and confirmed by microscopic examination of a wet mount with saline solution or culture of the parasite in media. Affected birds can be treated with several compounds, including carnidazole and metronidazole.
Trichomonosis in birds is an infection caused by protozoan parasites of the genus Trichomonas. In most cases, trichomonosis in domestic fowl, pigeons, doves, songbirds, and hawks is characterized by caseous oral accumulations and usually by weight loss. The disease has been termed “canker,” “roup,” and, in raptors, “frounce.”
Etiology of Trichomonosis in Birds
Both Trichomonas gallinae and T stableri cause trichomonosis in birds. These flagellated protozoa live in the sinuses, mouth, throat, esophagus, liver, and other organs. Genotype differences may be associated with a spectrum of virulence, but pathogenicity may be complicated by immune response and host species.
The etiologic agent of trichomonosis affecting birds is different from those affecting cattle and humans.
Epidemiology and Transmission of Trichomonosis in Birds
Trichomonosis in birds is more prevalent among domestic pigeons and wild doves than among domestic fowl, although severe outbreaks have been reported in chickens and turkeys. Some trichomonad strains cause high mortality rates in pigeons and doves.
Trichomonosis occurs worldwide except in Antarctica, Greenland, and northern parts of North America, Europe, and Asia. To date, the disease has been reported in birds in the orders Anseriformes, Columbiformes, Falconiformes, Galliformes, Gruiformes, Passeriformes, and Psittaciformes.
Predatory birds (raptors, crows, etc) may become diseased after eating infected birds and commonly show liver lesions, with or without throat involvement. Pigeons and doves transmit the infection to their offspring in contaminated crop milk.
Contaminated water is probably the most important source of infection for chickens, turkeys, and songbirds, and the parasites have been shown to survive from 2 to 24 hours in distilled water. Inadequate cleaning of outdoor birdbaths and waterers can contribute to transmission.
Trichomonosis in birds is not considered zoonotic.
Clinical Findings of Trichomonosis in Birds
The disease course of trichomonosis in birds is rapid.
The first lesions appear as small, yellowish areas on the oral mucosa. They grow rapidly and coalesce to form masses that frequently completely block the esophagus and can prevent the bird from closing its mouth. Fluid may accumulate in the oral cavity. Watery ocular discharge develops, and, in more advanced stages, exudate around the eyes can result in blindness.
Birds lose weight rapidly, become weak and listless, and sometimes die within 8–10 days.
Chronically infected birds appear healthy, although trichomonads are usually present in scrapings from the mucous membranes of the throat.
Lesions
Affected birds' throats may be riddled with caseous, necrotic foci. The mouth and esophagus contain a mass of necrotic material that may extend into the skull and sometimes through the surrounding tissues of the neck to involve the skin (see trichomonosis in dove image). In the esophagus and crop, lesions may be yellow, rounded, raised areas, with a central conical caseous spur, often referred to as “yellow buttons.”
The crop may be covered by a yellowish diphtheritic membrane that may extend to the proventriculus. In most birds, the gizzard and intestines are not involved.
Lesions of internal organs are most frequent in the liver; they vary from a few small yellow areas of necrosis to almost complete replacement of hepatic tissue by caseous necrotic debris. Adhesions and involvement of other internal organs appear to be contact extensions of hepatic lesions.
Courtesy of Dr. Kevin Keel.
Diagnosis of Trichomonosis in Birds
Histological examination
PCR assay
Confirmation by microscopic examination of wet mount with saline solution or culture from nonfrozen carcasses
Culture of organisms in prepared culture media
Lesions of trichomonosis in birds are characteristic but not pathognomonic; other differential diagnoses for these gross lesions in birds include salmonellosis, poxvirus, Capillaria spp infection, candidiasis, aspergillosis, and hypovitaminosis A. Trichomonosis has sometimes been confused with histomoniasis because of the similarity in hepatic lesions.
Diagnosis should be confirmed by microscopic examination of a direct smear of mucus or fluid from the throat to demonstrate the presence of trichomonads.
Trichomonads can be cultured in various artificial media, such as Diamond's medium, 0.2% Loeffler’s dried blood serum in Ringer’s solution, or a 2% solution of pigeon serum in saline (0.9% NaCl) solution. Good growth is obtained at 37°C (98.6°F).
If the carcass is fresh (dead < 48 hours) and has not been frozen, confirmation testing can be performed via microscopic evaluation of a wet mount of lesion material using saline (0.9% NaCl) solution showing motile trichomonads. Antimicrobials may be used to decrease bacterial contamination.
Samples should be examined by a veterinarian or diagnostician experienced with morphological ID of trichomonads. PCR assay is often used to determine Trichomonas genotype.
Treatment and Control of Trichomonosis in Birds
Control of trichomonosis in birds centers around sanitation and biosecurity.
Bird feeders, baths, and waterers can be major sources of infection for wild and domestic birds, so frequent cleaning of feeders and waterers is important to minimize transmission. If an outbreak of trichomonosis in wild birds is documented or suspected, feeders and waterers should be removed for approximately 2 weeks and cleaned with a 10% bleach solution.
Because trichomonads in pigeons are so readily transmitted from parent to offspring in the normal feeding process, chronically infected birds should be separated from breeding birds. In pigeons, recovery from infection with a less virulent trichomonad strain appears to provide some protection against subsequent attack by a more virulent strain.
In pigeons, successful treatments include carnidazole (10 mg/bird, PO, once), metronidazole (60 mg/kg, PO), or dimetridazole (15–60 mg/bird, PO, for 5 days).
Neither metronidazole not dimetridazole is approved for use in birds in the US; however, they could be used in an extralabel manner in birds by veterinary prescription, except in food-producing bird species (chickens and turkeys) and in minor-species birds (eg, game birds, ducks, geese, ostriches) intended for use as food, for which extralabel drug use of these drugs is prohibited.
Key Points
Trichomonosis is an emerging disease in songbirds and continues to be an important disease in doves, pigeons, and raptors.
Good sanitation of bird feeders and waterers is imperative to minimize transmission.
For More Information
Gerhold R. Parasitic Diseases. In: Greenacre CB, Morishita TY. eds. Backyard Poultry Medicine and Surgery: A Guide for Veterinary Practitioners. 2nd ed. Wiley; 2021:206-217.
McDougald LR, Cervantes HM, Jenkins MC, Hess M, Beckstead R. Protozoal infections. In Swayne DE, ed. Boulianne M, Logue CM, McDougald LR, Nair V, Suarez DL, associate eds. Diseases of Poultry. 14th ed. Wiley-Blackwell; 2020:1192-1254.
Gómez-Muñoz MT, Gómez-Molinero MÁ, González F, et al. Avian oropharyngeal trichomonosis: treatment, failures and alternatives, a systematic review. Microorganisms. 2022;10(11):2297.
