Avian Gastric Yeast (Macrorhabdosis)

Macrorhabdus ornithogaster, formerly known as “megabacteria,” is a Gram-positive yeast that affects psittacine (most commonly budgerigars) and non-psittacine birds.

Clinical Signs

Non-specific (“fluffed” bird), regurgitation, vomiting, loose stools, anorexia, chronic weight loss, emaciation, melena, anemia, sudden death


Fecal direct and gram stain
Caution: can be easily washed of slides
PCR >90% sensitivity
+/- Radiographs - to rule in/out other GI diseases
+/- Histopathology if death - do not separate proventriculus and ventriculus, organism lives in greatest numbers at the isthmus between them


Amphotericin B 100 mg/kg PO q 12 hours for 30 days
Fluconazole 10 mg/kg PO q 12 hours for 14 days
Effectiveness will vary by strain
Apple Cider Vinegar 15 mL/qt of drinking water


Good with early diagnosis and treatment


Recheck examination at 14 day mark or sooner if problems, fecal test at end of treatment