Update on the diagnosis and management of Macrorhabdus ornithogaster (formerly megabacteria) in avian patients.

Macrorhabdus ornithogaster, a yeast found only at the junction between the ventriculus and proventriculus, can infect a wide range of birds. Infection is often subclinical but can also result in gastrointestinal signs. Direct observation of the organism in the feces is a specific but somewhat insensitive means of diagnosis. At least three antifungal drugs are reported to be effective for treatment but resistance to one or more of these drugs may occur.