Throat,Cyst,and Crop Canker is a disease caused by the protozoan parasite Trichomonas gallinae. It mainly affects pigeons and is common in aviaries. The disease is often fatal.
Cause:                      
Trichomonas gallinae requires moisture to survive and lives in the crop and oesophagus, sometimes spreading to organs like the liver. It spreads through moist food and water. It dies quickly when dry, so diagnosis involves testing live or recently dead birds.
Clinical Signs:
The parasite irritates and ulcerates the crop lining, often leading to secondary bacterial infections. Birds may vomit (with vomit on their head from shaking), lose weight, and show yellow, cheesy deposits in the crop on post-mortem. Some birds carry the parasite without symptoms. The number of parasites often matches the severity of signs.