JPC SYSTEMIC PATHOLOGY

DIGESTIVE SYSTEM

September 2024

D-F06 (NP)

 

SIGNALMENT (JPC #4111382-00): 3 year old female budgerigar (Melopsittacus undulatus).

 

HISTORY: This budgerigar had a 1 year history of intermittent regurgitation. Previously, the bird was found to have Avian Bornavirus antibodies on bloodwork and avian gastric yeast on fecal exam. Despite treatment, this animal continued to regurgitate, died spontaneously, and was submitted for necropsy. At necropsy, a mass was identified at the ventricular/proventricular isthmus.

 

HISTOPATHOLOGIC DESCRIPTION: Proventriculus/Ventriculus Isthmus: Extending from the mucosa into the tunica muscularis is an unencapsulated, infiltrative, moderately cellular neoplasm composed of epithelial cells arranged in tubules on a scant fibrovascular stroma. Neoplastic cells have indistinct cell borders, a moderate amount of wispy to granular eosinophilic cytoplasm, a round to ovoid nucleus with finely stippled chromatin and 1-3 variably distinct nucleoli. Anisocytosis and anisokaryosis are mild and there are occasional mitotic figures. Neoplastic tubules contain variable amounts of smooth, amphophilic material (secretory product). 

 

On the luminal surface within the koilin layer and penetrating between glands are dense mats of rod shaped fungi that are 2x 20-40 µm and line up perpendicularly to the surface in a linear arrangement. Koilin is multifocally and extensively disrupted or lost. The mucosa and submucosa are multifocally expanded by an inflammatory infiltrate composed of lymphocytes, histiocytes and plasma cells. There is mild hyperplasia of the ventriculus epithelial cells characterized by disorganized piling of the mucosal epithelial cells up to 4 layers and increased mitotic figures. Mucosal glandular epithelial cells are occasionally swollen and vacuolated (degenerate) or rarely shrunken with hypereosinophilic cytoplasm and a pyknotic nucleus (necrosis)The serosa is moderately expanded by edema and inflammatory infiltrates composed of lymphocytes and plasma cells with fewer heterophils, and macrophages. 

 

MORPHOLOGIC DIAGNOSIS: 1. Ventriculus/proventricular isthmus: Adenocarcinoma, budgerigar (Melopsittacus undulatus), avian.

2. Ventriculus/proventricular isthmus: Proventriculitis and ventriculitis, lymphohistiocytic, multifocal, moderate with koilin loss and abundant surface-associaetd fungal yeast (Macrorhabdus ornithogaster), and mucosal epithelial hyperplasia and dysplasia.

 

ETIOLOGIC DIAGNOSIS: Proventricular and ventricular macrorhabdiosis (with proventricular adenocarcinoma)

 

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 (i.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 as presence may induce preneoplastic changes or be facilitated by these changes (Powers, Vet Pathol. 2019.)

 

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. Fletcher OJ, Abdul-Aziz T. Alimentary System. In:, Abdul-Aziz T, Fletcher OJ, Barnes HJ, eds. Avian Histopathology. 4^th ed. Madison, WI: Omnipress; 2016:272, 306-308.
2. Pascal A, Lee MD. Fungal infections. In: Swayne DE, ed. Diseases of Poultry. 14^th ed. Hoboken, NJ: Wiley &Sons; 2020:1128-1129.
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 M. 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 gen. 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: 806-807

 

 

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