A pigeon presents with anorexia and oral cavity exudate revealing pear-shaped flagellated protozoa. What is the most likely diagnosis?

The presentation of anorexia and oral cavity exudate in a pigeon, coupled with the observation of pear-shaped flagellated protozoa, strongly indicates an infection caused by Trichomonas. This protozoan specifically, often referred to as Trichomonas gallinae when affecting birds, is known to cause canker, or frounce, which leads to lesions in the oral cavity, esophagus, and proventriculus of birds, exemplified by the exudate described.

Trichomonas exhibits the characteristic pear shape with flagella that help in its motility, aligning with the clinical signs observed in this case. The disease caused by Trichomonas gallinae can lead to significant health issues in pigeons and other birds, making it crucial for accurate diagnosis and treatment.

The other choices do not align as well with the symptoms presented. Cystoisospora, Giardia, and Cryptosporidium also involve protozoan infections, but they are typically associated with different clinical signs and environments. For example, Giardia usually affects mammals and presents with gastrointestinal symptoms rather than oral cavity exudate. Cryptosporidium is known to cause similar gastrointestinal issues primarily in mammals. Therefore, the findings in this