JPC SYSTEMIC PATHOLOGY
SIGNALMENT (JPC #4111382-00): 2-year-old male common canary (Serinus canaria)
HISTORY: These canaries were acquired from a pet store, and subsequently used in an avian malaria study. Some birds tested positive for Cryptosporidium galli but failed to respond to therapy. The birds were euthanized at the end of the study. No gross lesions were noted.
HISTOPATHOLOGIC DESCRIPTION: Isthmus, ventriculus, proventriculus: Infiltrating approximately 60% of the length of the proventriculus and extending through the isthmus to ventriculus are 2 x 20 um, basophilic, rod-shaped yeast that are stacked end-to-end in a linear fashion and line the mucosa or rarely expand the lumen of superficial proventricular glands. Superficial proventricular mucosa has increased numbers of goblet cells. Scattered throughout the proventriculus, the glandular epithelial cells are occasionally swollen and vacuolated (degenerate) or rarely shrunken with hypereosinphilic cytoplasm and a pyknotic nucleus (necrosis). Multifocally, glands are mildly ectatic with luminal proteinaceous material. Within the lamina propria of the ventriculus and proventriculus, there are variable sized aggregates of lymphocytes and histiocytes and minimal fibrosis separating some glands. The koilin layer is diffusely attenuated with disorganization near the isthmus and a focal area of loss with replacement by aggregates of yeast.
Liver: Affecting less than 20% of the liver are variably sized nodules of lymphocytes and macrophages. Multifocally, there are random foci of Kupffer cells that contain a variably sized vacuole (lipogranulomas). (likely unrelated to the gastric yeast)
- Isthmus, ventriculus, proventriculus: Proventriculitis and ventriculitis, lymphocytic, histiocytic, multifocal, moderate with koilin attenuation, goblet cell hyperplasia, and numerous intralesional yeast, common canary (Serinus canaria), avian.
- Liver: Hepatitis, lymphohistiocytic, multifocal, chronic, moderate with lipogranulomas.
ETIOLOGIC DIAGNOSIS: Proventricular macrorhabdiosis
CAUSE: Macrorhabdus ornithogaster
SYNONYMS: avian gastric yeast, megabacteria
- First recognized as a disease resulting in wasting of budgerigars; now other birds are recognized to be affected
- Initially thought to be a bacteria (and named “megabacteriosis”) due to large, rod-like appearance of the yeast
- Gram positive, Periodic-acid Schiff positive, chitin positive, anamorphic, ascomycetous rod shaped, yeast
- Commonly found on the mucosa of the isthmus where it colonizes (e. junction between the ventriculus and proventriculus) in various avian species to include budgerigars, canaries, finches, parrotlets, ostriches
- less common in chickens, quail, turkey, gray partridges
- Stress may be a predisposing factor
- Transmission: possibly fecal-oral
- Detected in birds with and without clinical signs; may not cause disease in all cases
TYPICAL CLINICAL FINDINGS:
- May be subclinical in mild infections
- Acute: anorexia, regurgitation, death within 24-48 hours
- Chronic: polyphagia, regurgitation, diarrhea, weight loss (wasting)
TYPICAL GROSS FINDINGS:
- Excess mucus production
- Proventricular and ventricular ulceration
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Goblet cell hyperplasia with mononuclear inflammation
- Organisms form large aggregates on mucosal surface and within glands of the proventriculus, most commonly at the isthmus
- may extend to the koilin layers of the ventriculus, and to the caudal esophagus in severe cases
- Organism: 2 × 20-40µm; arranged end to end and in a “log jam” or matchstick configuration
- Koilin layer is disrupted, attenuated, and disorganized
- Ulceration in severe cases with lymphoplasmacytic and heterophilic inflammation +/- hemorrhage
- Surface scrapings of affected areas
- PCR of feces
- Subclinical infections are possible, and a positive PCR result does not guarantee disease
- Candidiasis: commonly found in the crop, mouth, pharynx, esophagus, and proventriculus; yeasts and septate fungal hyphae
- Trichomoniasis: commonly found in the mouth, pharynx, esophagus; flagellated protozoan typically found with abundant necrosis
- Boulianne M, et al. Avian Disease Manual. 7th Jacksonville, FL: AAAP;2013:30-34.
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- Phalen DN. Update on the diagnosis and management of Macrorhabdus ornithogaster (formerly megabacteria) in avian patients. Vet Clin North Am Exot Anim Pract. 2014 May;17(2):203-210.
- Schmidt RE, Reavill DR, Phalen DN. In: Schmidt RE, Reavill DR, Phalen DN. eds. Pathology of Pet and Aviary Birds, Second Edition. Iowa State Press.. Ames, Iowa. 2015: 65, 70, 81.
- Smith JA. Passeriformes (songbirds, perching birds). In: Miller RE, Fowler M, eds. Fowler"s Zoo and Wild Animal Medicine. Vol 8. St. Louis, MO: Elsevier; 2015:243.
- Snyder JM, Treuting PM. Pathology in practice. Adenocarcinoma of the proventriculus with liver metastasis and marked, diffuse chronic-active proventriculitis and ventriculitis with moderate M. ornithogaster infection in a budgerigar. J Am Vet Med Assoc. 2014; 15;244(6):667-669.
- Tomaszewski EK, Logan KS, Snowden KF, et al. 2003. Phylogenetic analysis identifies the “megabacterium” of birds as a novel anamorphic ascomycetous yeast, Macrorhabdus ornithogaster nov., sp. nov. Int J Syst Evol Microbiol. 2003; 53(4):1201–1205.