JPC SYSTEMIC PATHOLOGY
DIGESTIVE SYSTEM
August 2021
D-F06 (NP)

 

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, and proventriculus:  Lining the mucosa of approximately 60% of the length of the proventriculus, rarely expanding superficial proventricular glands, and extending along the mucosa through the isthmus to the ventriculus are myriad 2 x 20 um, basophilic, elongate, rod-shaped yeast that are primarily lined up perpendicularly to the mucosal surface and stacked end-to-end in a linear fashion.  The superficial proventricular mucosa has increased numbers of goblet cells (goblet cell hyperplasia). Scattered throughout the proventriculus, glandular epithelial cells are occasionally swollen and vacuolated (degenerate) or rarely shrunken with hypereosinophilic cytoplasm and a pyknotic nucleus (necrosis).  Multifocally, proventricular glands are mildly ectatic with luminal proteinaceous material.  The lamina propria of the ventriculus and proventriculus contains few variably sized aggregates of lymphocytes and histiocytes with minimal fibrosis that separate some glands.  The koilin layer is diffusely attenuated and is disorganized near the isthmus, and there is a focal area of loss with replacement by aggregates of yeast.

 

Liver: Affecting approximately 5% of the liver are variably sized, random nodules of lymphocytes and macrophages.  Multifocally, there are random foci of Kupffer cells that contain a variably sized, discrete, round, lipid vacuole (lipogranulomas).

 

MORPHOLOGIC DIAGNOSIS: 1. Isthmus, ventriculus, proventriculus: Proventriculitis and ventriculitis, lymphohistiocytic, multifocal, mild, with koilin attenuation, goblet cell hyperplasia, and numerous surface-associated yeast, common canary (Serinus canaria), avian.

2. Liver: Hepatitis, lymphohistiocytic, multifocal, chronic, moderate, with lipogranulomas.

 

ETIOLOGIC DIAGNOSIS: Proventricular macrorhabdiosis

 

CAUSE:  Macrorhabdus ornithogaster

 

SYNONYMS:  avian gastric yeast, megabacteria

 

GENERAL DISCUSSION:

• 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 (e. junction between the ventriculus and proventriculus) in various avian species (e.g. budgerigars, canaries, finches, parrotlets, ostriches)
  • less common in chickens, quail, turkey, gray partridges
• Associated with proventricular adenocarcinoma in budgerigars; nature of association not determined (Powers, Vet Pathol.)

 

PATHOGENESIS:

• 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
• Enlarged, distended, discolored proventriculus with wall thickening
• Proventricular and ventricular ulceration and hemorrhage
• Emaciation

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:

• Goblet cell hyperplasia with mononuclear inflammation (lymphoplasmocytic and histiocytic)
• 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

 

ADDITIONAL DIAGNOSTICS:

• Surface scrapings of affected areas
• PCR of feces
• Subclinical infections are possible, and a positive PCR result does not guarantee disease

 

DIFFERENTIAL DIAGNOSIS:

• Candidiasis: commonly found in the crop, mouth, pharynx, esophagus, and proventriculus; yeasts, pseudohyphae, and septate fungal hyphae
• Trichomoniasis: commonly found in the mouth, pharynx, esophagus; flagellated protozoan typically found with abundant necrosis

 

References:

1. Boulianne M, et al. Avian Disease Manual.  7^th  Jacksonville, FL: AAAP;2013:30-34.
2. Jordan FTW, Hampson DJ. Some other bacterial diseases. In: Pattison M, McMullin P, Bradbury J, Alexander D. eds. Poultry Diseases. Sixth Edition. Elsevier. Ithaca, New York. 2007: 249.
3. Phalen DN. Update on the diagnosis and management of Macrorhabdus ornithogaster (formerly megabacteria) in avian patients. Vet Clin North Am Exot Anim Pract. 2014;17(2):203-210.
4. Powers LV, Mitchell MA, Garner, MM. Macrorhabdus ornithogaster Infection and Spontaneous Proventricular Adenocarcinoma in Budgerigars (Melopsittacus undulates).  Vet Pathol.  2019; 56(3): 486-493.
5. 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.
6. 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.
7. Snyder JM, Treuting PM. Pathology in practice. Adenocarcinoma of the proventriculus with liver metastasis and marked, diffuse chronic-active proventriculitis and ventriculitis with moderate ornithogaster infection in a budgerigar. J Am Vet Med Assoc. 2014; 15;244(6):667-669.
8. 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.
9. Trupkiewicz J, Garner MM, Juan-Salles C. Passeriformes, Caprimulgiformes, Coraciiformes, Piciformes, Bucerotiformes, and Apodiformes. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. Cambridge, MA: Elsevier; 2018: 812.

 

 

 

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