Trichomonosis in domestic fowl, pigeons, doves, songbirds, and hawks is characterized, in most cases, by caseous accumulations in the throat and usually by weight loss. It has been termed “canker,” “roup,” and, in hawks, “frounce.”
Etiology
Both Trichomonas gallinae and T stableri are causative organisms of trichomonosis. These flagellated protozoa live in the sinuses, mouth, throat, esophagus, liver, and other organs. Trichomonosis 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 in pigeons and doves. Hawks 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 pigeon milk. Contaminated water is probably the most important source of infection for chickens, turkeys, and songbirds, and the parasite has been shown to survive at least 2 hours and potentially up to 24 hours in distilled water. Cleaning of outside bird baths and waterers frequently is important to minimize transmission.
Clinical Findings
The disease course of trichomonosis 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 may prevent the bird from closing its mouth. Much fluid may accumulate in the mouth. There is a watery ocular discharge and, in more advanced stages, exudate about the eyes that may result in blindness. Birds lose weight rapidly, become weak and listless, and sometimes die within 8–10 days. In chronic infections, birds appear healthy, although trichomonads can usually be demonstrated in scrapings from the mucous membranes of the throat.
Lesions
Courtesy of Dr. Jean Sander.
Oral cavity of a pigeon with lesions consistent with trichomonosis, including caseous necrosis. Further diagnostic testing is needed to confirm trichomonosis because other parasitic, bacterial, fungal, and viral diseases have similar gross lesions.
The bird 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. In the esophagus and crop, the 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. The gizzard and intestine 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 liver tissue by caseous necrotic debris. Adhesions and involvement of other internal organs appear to be contact extensions of the liver lesions.
Diagnosis
Gross lesions may be suggestive for trichomonosis but infection is confirmed by saline wet mount or culture from nonfrozen carcasses to observe characteristic undulating movement of trichomonads.
Additional diagnostic tests include histopathology and PCR.
Lesions of trichomonosis are characteristic but not pathognomonic; those of pox, fungal disease, Salmonella, and other infections can be similar. Trichomonosis has sometimes been confused with histomoniasis Histomoniasis read more because of the similarity in liver lesions. Diagnosis should be confirmed by microscopic examination of a smear of mucus or fluid from the throat to demonstrate the presence of trichomonads. Trichomonads can be cultured easily in various artificial media such as Diamond’s media, 0.2% Loeffler’s dried blood serum in Ringer’s solution, or a 2% solution of pigeon serum in isotonic salt solution. Good growth is obtained at 98.6°F (37°C). Antibiotics may be used to reduce bacterial contamination. PCR is often used to determine the Trichomonas genotype.
Control
Control of trichomonosis centers around sanitation and biosecurity. Bird feeders, baths, and waterers can be a major source of infection for wild and domestic birds, so frequent cleaning of feeders and waterers is important to minimize transmission. If an outbreak of trichomonosis is documented or suspected, feeders and waterers should be removed for
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. Successful treatments include carnidazole (10 mg/kg body wt), metronidazole (60 mg/kg body wt), and dimetridazole (50 mg/kg body wt, PO; or in the drinking water at 0.05% for 5–6 days). None of these drugs is approved for use in birds in the USA, but they could be used in non-food-producing birds by veterinary prescription.
Key Points
Trichomonosis is an emerging disease in songbirds and continues to be important disease for doves, pigeons, and raptors.
Good sanitation of bird feeders and waterers is imperative to minimize transmission.
Trichomoniasis is an infectious disease of birds caused by the single-celled protozoan Trichomonas gallinae and Trichomonas stableri. The parasite inhabits the upper digestive tract, mainly the crop and esophagus. While some strains of the protozoa do not cause disease, others can result in death. In pigeons and doves this disease is also known as Canker, in raptors it is known as Frounce. Trichomoniasis is one of the oldest known wildlife diseases with written records dating back to the 1500s. The protozoan responsible for the disease was not isolated until 300 years later.
Significance
Trichomoniasis is considered the most important disease of mourning doves in North America and can result in major mortality events in these species. The largest outbreak of trichomoniasis occurred between 1950-1951 in Alabama and neighboring states resulting in the death of 50,000 to 100,000 mourning doves. Since it is a feeder-associated disease, it may also lead to serious population declines in some species of songbird.
Species Affected
Trichomoniasis is primarily a disease of pigeons and doves, but raptors are also commonly affected. On rare occasions waterfowl and upland game birds have been affected. Domestic turkeys, chickens, and other captive birds can also be infected. T. gallinea and T. stableri are not known to infect humans.
Distribution
Trichomoniasis occurs in birds worldwide except Antarctica, Greenland, and the northern reaches of North America, Europe, and Asia. The protozoa likely occurs wherever rock pigeons and mourning doves are found.
Transmission
Adults birds are the reservoir host for this organism. The protozoa are shed into the environment in the oral secretions of infected birds. Protozoa may directly pass from one adult to another through bill-to-bill contact, which is common during courtship. Young doves and pigeons acquire the protozoa when they receive regurgitated food from infected adults during feeding. Susceptible birds may also consume T. gallinae and T. stableri in contaminated food or water. The protozoa are transmitted to raptors when they feed on infected birds.
T. gallinae and T. stableri are killed by drying but can survive for up to 5 days in moist grain and 20 minutes to several hours in water. Supplemental feeding and other practices that congregate susceptible bird species can lead to local mortality.
Clinical Signs
Clinical trichomoniasis is primarily a disease of young pigeons and doves and is often fatal. 80-90% of adult pigeons carry T. gallinae and/or T. stableri but show no clinical signs of illness. The severity of the disease depends on the susceptibility of the bird and the pathogenicity of the strain of the parasite. Mild infections can produce immunity to more virulent strains.
The protozoa inhabit the upper digestive tract of all affected birds, leading to inflammation of the lining of the mouth and esophagus, which can develop into cheese-like masses. The lesions within the upper digestive tract grow rapidly and coalesce to form masses that frequently interfere with eating and drinking. Birds that are unable to swallow often become emaciated and listless. Affected birds may also exhibit ruffled feathers, be unable to close their mouth, develop ocular discharge, diarrhea, and have difficulty breathing. Their necks and faces often appear puffy or swollen. Birds lose weight rapidly and usually die within 8-10 days from starvation because they cannot swallow or suffocate due to blockage of the trachea.
Diagnosis
A presumptive diagnosis can be made based on the presence of classic lesions on necropsy. Laboratory identification of the organism microscopically, by culture or PCR, is required for a definite diagnosis.
Treatment
Medications are available that can successfully treat trichomoniasis in birds. Captive birds can be treated by oral administration of the medication or by adding the medication to food and water. Treatment is challenging and likely not feasible in wild populations.
Management
Management of trichomoniasis centers around sanitation and biosecurity. Doves and pigeons should be prevented from congregating in large groups, particularly at birdbaths and feeders. Where feeding does take place, both food and water should be kept fresh and changed daily. Feeders, platforms, and other associated surfaces should be decontaminated regularly with a 10% bleach solution (9 parts water: 1 part bleach). Infected captive birds (symptomatic and asymptomatic carriers) should be culled or treated.
Suggested Reading
- Cole, R. A. Trichomoniasis. Pages 201-206 in M. Friend, and J. C. Franson, technical editors. Field Manual of Wildlife Diseases: Birds. United States Geological Survey.
- Forrester, D. J., and G. W. Foster. 2008. Trichomonosis. Pages 120-153 in C. T. Atkinson, N. J. Thomas, and D. B. Hunter, editors. Parasitic Diseases of Wild Birds. Wiley-Blackwell, Ames, Iowa, USA.
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