Trichomoniasis

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Other names: Canker, Frounce, Avian trichomoniasis

Cause

Trichomoniasis is an infectious disease of birds caused by the single-celled protozoan Trichomonas gallinae. There are several different strains of this protozoan, some that cause clinical disease while others do not. This disease is also known as canker in pigeons and doves, and frounce in raptors. 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 during 1950 to 1951 in Alabama and neighboring states and resulted in the death of 50,000 to 100,000 mourning doves. Since it is a feeder-associated disease, it may 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. This protozoan is not known to infect humans.

Distribution

Trichomoniasis occurs in birds worldwide except Antarctica, Greenland, and the northern reaches of North America, Europe, and Asia. T. gallinae likely occurs wherever rock pigeons and mourning doves are found

Transmission

Adults 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 in contaminated food or water. The protozoa 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. The protozoa are transmitted to raptors when they feed on infected birds.

Clinical Signs

Clinical trichomoniasis is primarily a disease of young pigeons and doves. 80-90% of adult pigeons carry T. gallinae, but show no clinical signs of illness. The protozoa inhabit the upper digestive tract of all affected birds, meaning there is often inflammation of the lining of the mouth and esophagus, which can develop into cheese-like masses. The lesions within the upper digestive tract may interfere with eating and drinking. Birds that are unable to swallow often become emaciated and listless. Affected birds may also exhibit ruffled feathers, diarrhea, and difficulty breathing. Their necks and faces often appear puffy or swollen. Birds usually die from starvation because they cannot swallow, or suffocate because of lesions in the mouth block the trachea.

Diagnosis

Trichomoniasis is diagnosed by laboratory identification of the T. gallinae protozoan. A presumptive diagnosis can also be made based on the presence of classic lesions on necropsy.

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 because of the inability to control food and water choices.

Management

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.
  • Michigan Department of Natural Resources. Wildlife Disease. Trichomoniasis.