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Trichomoniasis is caused by Trichomonas gallinae, a single-celled, pear-shaped protozoan with 4 whip-like anterior flagella and a fin-like undulating membrane that extends for approximately 2/3 of the total body length. The protozoan moves by undulation and flagellar action. Trichomoniasis is also known as Canker (in doves and pigeons) and as Frounce (in raptors). T. gallinae is a parasite of the upper digestive tract of many avian species causing accumulation of necrotic material in the mouth and esophagus. It is principally a disease of young birds and is often fatal. Nearly all pigeons and doves harbor the organism and can be a source of infection (in one case, 80-90% of adult pigeons were infected, but exhibited no clinical signs). There are avirulent strains which do not cause disease and highly virulent strains that circulate within bird populations causing disease and death. The severity of the disease to the bird depends on the susceptibility of the bird and the pathogenic potential of the strain of the parasite.
Trichomoniasis is cosmopolitan in distribution. In captive birds, the disease has been found in domestic or common pigeons, doves, quail, turkeys, chickens, falcons, hawks, various finches, the Java sparrow, and canaries. In wild birds, the disease has been found in doves and feral pigeons throughout the U.S. In Michigan, mourning doves and feral pigeons have been positive for trichomoniasis. The disease is believed to have been first introduced to North America when infected doves were brought from France to Nova Scotia in the early 1600's. Trichomoniasis is the most important disease of Mourning Doves in North America.
Transmission of T. gallinae occurs by discharge of bodily fluids in one of four ways. Adult doves and pigeons infect their offspring during feeding, infect other adult birds through contaminated food, water, and bedding and via courtship behavior. Raptors are infected through consumption of infected doves or pigeons.
This is a disease primarily of doves and pigeons and is transmitted from the adult to their offspring by the regurgitational method of feeding used by these birds. T. gallinae is present in the back of the throat of carrier birds (carrier birds may carry the infection for a year or longer). The trichomonads can easily mix with food and the pigeon milk that is produced in the crop of the bird and be transmitted when the parent bird regurgitates this mixture to its offspring. Oftentimes the offspring is infected at its first feeding which can occur minutes after hatching. This infection may become asymptomatic or may progress to a fatal case in 4 to 18 days post-infection.
Transmission via contamination of food and water occurs when the bird has extensive oral lesions and is unable to swallow food material or water. This results in pieces of grain or water being placed in the mouth, contaminated by organisms, and then dropped back on the ground, in the feeder, or in the water source. When another bird feeds or drinks in this location, T. gallinae is ingested and an infection may result. This organism can live at least 5 days on some moist grains and 20 minutes to several hours in water. The organism is extremely sensitive to desiccation (drying) as there is no cyst or resistant stage of the life cycle. Bedding is infected with the organism via fecal contamination.
During courtship, doves and pigeons have direct bill to bill contact during cross feeding and billing (touching of bills).
Birds of prey contract an infection by consuming infected doves or pigeons.
Birds infected with T. gallinae display a variety of clinical signs. The birds are depressed, salivate excessively, are emaciated, appear listless, ruffled and dull, have difficulty closing their mouth, display repeated swallowing movements, exhibit open mouth and noisy breathing, have watery eyes, have difficulty eating and drinking, have difficulty standing or maintaining their balance, have diarrhea, may have a puffy appearance of the neck, exhibit a sunken and empty crop and have a fetid odor. Birds will usually die from starvation due to the blockage of the esophagus or from suffocation caused by blockage of the trachea by the caseous (cheese-like) necrotic masses in the mouth commonly seen with this disease.
The pathology associated with trichomoniasis in doves and pigeons usually involves young birds and consists of the formation of caseous necrotic masses in the upper digestive tract and occasionally in the viscera. The first (acute) lesions appear in the mouth, pharynx, esophagus, and crop and consist of inflammation and development of creamy-white, wet, and sticky exudate on the mucosal surface (lining). The lesions progress to small, well-defined raised yellow-white ulcers. As the disease progresses further (chronic), the mucosal lesions become yellow in color, larger in size, hard, caseous coalesced masses that may invade the sinuses of the skull, extend externally to the beak and eyes, penetrate through the base of the skull into the brain and penetrate the viscera causing necrotic areas in the liver, spleen, pancreas, heart, lungs and air sacs. In raptors, liver and abdominal lesions are the main pathological changes that occur.
Diagnosis of trichomoniasis is based on history, clinical signs, lesions, and identification of the organism microscopically and by culturing. Gross lesions consist of yellow-white caseous necrotic obstructive nodules in the oral cavity, esophagus and crop. Microscopically (under low power magnification) the trichomonad organism can be found in the saliva (oftentimes stained green) or in smears of the cheese-like necrotic lesions in the upper digestive tract. These samples must be collected within 48 hours of the bird's death to be viable.
Treatment is only feasible in captive birds because the drugs used for treatment must be administered orally, either by force feeding or by treating the food and/or water. Antiprotozoal medications that have been used are Dimetridazole, Metronidazole (Flagyl), Copper sulfate, Quaternary Ammonia, Carnidazole, Enheptin (curing carrier birds), Emtryl (1,2-dimethyl-5-nitroimidazole), and Aminonitrothiazole. Some of these medications are under review and some can be specifically used only on non-food birds (Metronidazole). Treatment of wild birds is difficult because of the availability of natural food and water sources.
In order to control trichomoniasis, sources of infection need to be eliminated. In captive birds, cull or treat carrier birds, cull adults whose offspring become infected, regularly disinfect food and water sources with 10% bleach solution, screen out (exclude) wild birds to protect from contamination by wild pigeons and other birds, segregate young birds from adults, and segregate susceptible birds from recovered or carrier birds. In wild birds, minimize dove and pigeon concentrations at feeders (or do not feed) and water receptacles, stock tanks, livestock feedlots and grain storage facilities. Severely affected captive or wild birds should be euthanized. Mild infections will produce an immunity to more virulent strains of T. gallinae.
Trichomonas gallinae has never been reported to infect humans and is of no public health significance. In isolated populations of doves, trichomoniasis can serve as a significant mortality factor. Research on Cooper's hawks in urban areas of Tucson, Arizona reported high mortality in nestlings due to trichomoniasis infection. In Michigan, peregrine falcon chicks handled for banding purposes have, in the past, been treated with metronidazole to prevent infection.