Overview of Trichomonosis
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.”
Both Trichomonas gallinae and a newly recognized species, T stableri, are the 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 20 min in distilled water.
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.
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.
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 (see Histomoniasis) 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.
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. Bird feeders and waterers should be cleaned regularly and if an outbreak of trichomonosis is documented or suspected, feeders and waterers should be removed for ~2 wk and cleaned with a 10% bleach solution.