Canker is a parasitic infection of the mouth, throat, and crop in chickens caused by a single-celled organism called Trichomonas gallinae. It produces yellowish or white cheesy-looking lesions inside a bird’s mouth and throat that can interfere with eating, breathing, and swallowing. The disease is extremely common in pigeons and doves, with 80 to 90 percent acting as carriers, and it spreads to chickens through shared water sources or direct contact with infected birds.
What Causes Canker
The organism behind canker is a tiny flagellated protozoan, a microscopic parasite that propels itself with whip-like tails. It lives in the sinuses, mouth, throat, esophagus, and crop, and its preferred territory is the upper digestive tract. The parasite rarely moves past the proventriculus (the glandular stomach that sits just below the crop). In severe or advanced infections, though, it can spread to the liver and other internal organs.
Trichomonas gallinae damages tissue by releasing proteins that break down cell layers in the lining of the throat and crop. This is what creates the characteristic raised, cheese-like plaques that are the hallmark of the disease. The lesions start small but can grow quickly, especially in young or immunocompromised birds.
How It Spreads
Wild pigeons and doves are the primary reservoir. If wild birds drink from the same water dishes or feeders your chickens use, the parasite can pass between them easily. Trichomonas gallinae survives in standing water, so communal water sources are the biggest risk factor in backyard flocks. The organism can also spread through billing (direct beak-to-beak contact) and when parent birds feed crop milk or regurgitated food to their young, which is why squabs and chicks are especially vulnerable.
Unlike bacteria or viruses, this parasite doesn’t survive long outside a host or a water source. It needs moisture. Dry feeders and clean, frequently changed water go a long way toward breaking the transmission cycle.
Symptoms to Watch For
The most obvious sign is yellow or white caseous (cheese-textured) lesions inside the mouth and throat. You may notice them on the roof of the mouth, around the tongue, or deeper in the throat if you open the bird’s beak. Other signs include:
- Difficulty swallowing or reluctance to eat. Birds may pick at food but drop it, or stop eating entirely.
- Weight loss and lethargy. Infected chickens often become listless and visibly thinner over days to weeks.
- Foul-smelling breath. The decaying tissue in the mouth produces a noticeable odor.
- Drooling or mucus from the beak. As lesions grow, excess saliva and discharge accumulate.
- Nasal or eye discharge. In some cases the infection spreads to the sinuses, causing swelling around the eyes or runny nostrils.
- Labored breathing. If lesions grow large enough to obstruct the throat, the bird may gasp or stretch its neck to breathe.
Young birds are hit hardest. Adult chickens sometimes carry the parasite with mild or no visible symptoms, while chicks can deteriorate rapidly. In severe cases, lesions in the esophagus can grow large enough to completely block the opening, causing the bird to suffocate. There have also been rare cases where lesions inside the oral cavity grew so large they penetrated through the base of the skull into the brain.
Diagnosis
A veterinarian typically diagnoses canker by swabbing the inside of the bird’s mouth, placing the sample in a drop of saline on a slide, and examining it under a microscope. The parasites are visible as pear-shaped organisms with their characteristic flagella still moving. This “wet mount” method is quick and reliable when the infection is active. The visible mouth lesions themselves are also fairly distinctive, though they can sometimes be confused with other conditions like wet pox, vitamin A deficiency, or fungal infections.
Treatment Options and Legal Restrictions
Here’s where things get complicated for chicken keepers. The most effective drugs against Trichomonas gallinae belong to a class called nitroimidazoles, which includes metronidazole and dimetridazole. These drugs are widely used to treat canker in pet pigeons, parrots, and other non-food birds. However, in the United States, nitroimidazoles are completely prohibited for use in any food-producing animal, including chickens raised for eggs or meat. The FDA classifies them as Group I prohibited drugs with no allowable extra-label use, meaning a veterinarian cannot legally prescribe them for your laying hens or broilers.
This leaves backyard chicken keepers with fewer options. Some poultry keepers use acidified copper sulfate in drinking water as a preventive measure, typically at a rate of about one-quarter teaspoon per gallon of water given two to three times per week. This approach is more commonly used in pigeons, and its effectiveness against active canker infections in chickens is less well established than prescription antiparasitic drugs. If you suspect canker in your flock, working with an avian veterinarian is the most practical path, as they can evaluate what treatments are legally available for your situation and confirm the diagnosis.
Prevention and Biosecurity
Preventing canker is largely about controlling contact with wild birds and keeping water clean. These steps make a real difference:
- Change water daily. Trichomonas thrives in standing water. Dump, scrub, and refill waterers every day rather than just topping them off.
- Block wild bird access. Cover runs with netting or hardware cloth to keep pigeons and doves from landing near feeders and waterers. Even partial barriers help.
- Quarantine new birds. Keep any new chickens, especially those from swaps or unknown flocks, separated for at least 30 days before introducing them to your existing birds. Clean your hands, shoes, and equipment when moving between the two groups.
- Don’t share equipment. Avoid borrowing feeders, waterers, or tools from other poultry keepers. If you must, disinfect everything thoroughly before use.
- Clean enclosures regularly. Wash surfaces with dish soap first to remove organic material, then apply a commercial disinfectant according to the label directions. Most disinfectants only work on already-clean surfaces and need to sit for the time specified on the label, usually between 30 seconds and 10 minutes.
Dedicated shoes or boots for the coop area also help prevent you from tracking pathogens between your flock and the outside world.
Can Humans Get Canker From Chickens
The short answer is that the risk is very low but not zero. A related organism, Tetratrichomonas gallinarum (a different species from the one that causes canker), has been identified in human lung and oral cavity samples in a small number of cases. Genetic studies suggest that zoonotic transfer of trichomonad parasites between birds and humans has occurred on at least a couple of occasions. That said, regular and sustained transmission from birds to people has not been established. Standard hygiene, washing your hands after handling birds or cleaning their enclosures, is sufficient precaution for most people.