JPC SYSTEMIC PATHOLOGY

RESPIRATORY SYSTEM

September 2023

P-F01

 

 

Signalment (JPC #1901803): 7-year-old female German shepherd dog

 

HISTORY: This dog had a 6 mm diameter polypoid nodule in the nasal cavity.

 

HISTOPATHOLOGIC DESCRIPTION: Nasal mucosa: Diffusely, the subepithelial connective tissue (lamina propria) is moderately expanded by increased fibrous connective tissue, hemorrhage, fibrin, eosinophilic cellular and karyorrhectic debris, increased clear space (edema), and many viable and necrotic neutrophils, lymphocytes and plasma cells, fewer macrophages, and scattered hemosiderophages.  Admixed are various stages of extracellular juvenile and intact or collapsed mature sporangia. Juvenile sporangia are round, 10 to 50 µm in diameter, with a 2 µm thick wall and a single nucleus surrounded by granular cytoplasm. Mature sporangia are round, up to 220 µm in diameter with a 2-3 µm thick bilamellar wall and contain abundant immature and mature endospores with a thin wall, and clear cytoplasm. Diffusely, the mucosal epithelium is hyperplastic and forms polypoid projections with frequent transmigrating neutrophils. The nasal cavity contains an exudate composed of viable and necrotic neutrophils, numerous endospores, mucinous material, necrotic debris, and hemorrhage. Small caliber blood vessels are often lined by plump (reactive) endothelium. Vessels occasionally contain 1 to 2 intravascular 6-8 µm microfilaria.

 

MORPHOLOGIC DIAGNOSES: 1. Nasal mucosa: Rhinitis, proliferative, neutrophilic and lymphoplasmacytic, chronic-active, diffuse, moderate, with fibrosis, and multiple extracellular juvenile and mature sporangia with numerous endospores, German shepherd dog, canine.

2. Nasal mucosa, blood vessels: Intravascular microfilariae, few.

 

ETIOLOGIC DIAGNOSIS: Nasal rhinosporidiosis

 

CAUSE: Rhinosporidium seeberi

 

GENERAL DISCUSSION:

• Aquatic protistan parasite in the class Mesomycetozoea
• Rhinosporidium seeberi is a sporadic cause of nasal polyps in horses, and occurs less often in cattle, dogs, cats, goats, and waterfowl
• Endemic in wet tropical and subtropical environments, uncommon in North America and Africa, rare in Europe
• R. seeberi has a predilection for large breed male dogs and male horses
• Canine lesions have only been reported in the nasal cavity; lesions in other species may occur on the pinna, skin, and mucosal surfaces

           

PATHOGENESIS:  

• Infection associated with exposure of mucosa to contaminated water sources
• The natural host or reservoir is unknown

 

LIFE CYCLE:

• Infective spore penetrates mucosa > localizes in subepithelial connective tissue > develops into juvenile sporangium (trophocyte) > development through immature, intermediate, and mature sporangium > moist environments (e.g. mucus membranes) stimulate release of endospores through an apical pore into tissue or nasal exudate
• Development from juvenile to mature sporangia accompanied by changes in the thickness and lamination of the walls; a nucleus appears and the cytoplasm condenses to form endospores

 

TYPICAL CLINICAL FINDINGS:  

 

TYPICAL GROSS FINDINGS:  

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:  

• Fibrovascular polyp lined by squamous or columnar hyperplastic epithelium, often ulcerated with fibrosis and embedded large sporangia of various life stages

• Juvenile sporangia: 15-75 µm in diameter, with a single central basophilic nucleus and unilamellar PAS-positive wall
• Mature sporangia: 100-500 µm in diameter, spherical, with a 2-5 µm thick bilamellar wall; contains hundreds of 5-10 µm endospores that contain internal eosinophilic globules and are surrounded by a bilamellar cell wall
• Empty, collapsed sporangia that have expelled endospores into the lumen; often surrounded by lymphoplasmacytic, neutrophilic, and sometimes granulomatous inflammation

• In general, evidence of endosporulation includes: Mature sporangia containing numerous endospores, sporangia ruptured into adjacent tissue, free endospores within tissue, and empty sporangia
• Variable inflammation composed of lymphocytes, plasma cells, and macrophages

 

ADDITIONAL DIAGNOSTIC TESTS:  

• Histochemical stains: Wright Gridley’s, toluidine blue, periodic acid-Schiff (PAS), and Grocott's 
• Cytology

• Spores: 5-15 µm in diameter; slightly refractile capsule with numerous, round, eosinophilic structures (spherules); PAS staining facilitates identification of spores
• Sporangia: 30-300 µm in diameter, globoid; undergo sporulation to contain abundant small round endospores; better visualized on unstained specimens
  • Endospores: Three stages of maturation discernible when using Romanowsky stains
    • Mature endospores (predominate over immature and intermediate endospore cytologically): 8-15 µm in diameter, with a thick, hyalinized cell wall and pale magenta to non-staining halo
    • Immature endospores: 2-4 µm in diameter, with lightly basophilic cytoplasm and a pink to purple nucleus that fills up to ½ of the endospore, and one to two smaller round magenta structures
    • Intermediate endospores: Rarely described; 5-8 µm in diameter spherical, granular, and basophilic structures containing eosinophilic to globular internal structures and a variably sized clear halo
  • Rosetting of inflammatory cells around spores, especially neutrophils, is a feature considered to facilitate spore identification

• PCR, DNA sequencing

 

DIFFERENTIAL DIAGNOSIS:  

• Canine rhinitis

• Aspergillus sp. (P-F06) and Penicillium sp: Necrotizing and granulomatous rhinitis; 5-7 µm septate fungal hyphae with parallel walls and dichotomous, acute angle branching
• Coccidioides immitis (P-F03, C-F01): Suppurative to pyogranulomatous rhinitis; spherules 20-200 µm in diameter with double contoured, refractile walls and 2-5 µm diameter endospores
• Cryptococcus neoformans (P-F04): Sporadic cause of rhinitis; 2-20 µm diameter yeast-like basidiomycete, with a 2-10 µm (thick) mucopolysaccharide capsule, narrow-based budding 
• Blastomyces dermatitidis (P-F05): Granulomatous rhinitis; round, 5-20 µm yeast with a distinct, often refractile, 1-2 µm wall; broad-based budding

• Other organisms that endosporulate 

• Fungi
  • Coccidioides immitis (see above)
  • Emmonsia sp.: Cause of pulmonary adiaspiromycosis  in small rodents, carnivores, and mustelids; thick-walled, non-budding, non-replicating adiaspores in lung tissue; lacks internal spores (can use to distinguish from C. immitis)
  • Batrachochytrium dendrobatidis (chytrid fungus)(I-F10): Amphibian pathogen; ubiquitous fungus and only known chytrid to parasitize vertebrates; infection often restricted to keratinized skin; three stages of thalli, including a uninucleate form (homogenous basophilic cytoplasm), a multinucleate form (lightly stippled to vacuolated cytoplasm +/- internal septation), and cyst-like form (zoosporangium containing 2-3 µm round to oval basophilic spores)
• Algae
  • Prototheca spp. (D-F03, S-M03, U-M25): Unicellular, saprophytic algae capable of causing enteric, cutaneous, nasal, mammary, neurologic, or disseminated granulomatous disease predominantly in dogs, cats, and cattle; sporangia 10-20 µm in diameter with a 2-3 µm thick amphophilic cell wall and a basophilc nucleus, or sporangia undergoing endosporulation with wedge-shaped, radially arranged, angular endospores separated by septations (“Mercedes Benz” symbol); achlorous (used to differentiate from Chlorella sp.)
  • Chlorella sp. (a cause of green algal infections): Spherical algal cells ~9 µm in diameter, with a thin refractile wall, single basophilic round nucleus, and amphophilic to eosinophilic granular cytoplasm; larger algal cells (sporangia) filled with 2-6 µm daughter cells (sporangiospores or endospores)

 

COMPARATIVE PATHOLOGY:  

• Rhinosporidiosis is uncommon in cattle, goats, and waterfowl, and very rare in cats
• Exotics and zoo species
  • Ducks, geese, swans: Rarely reported; polyps of conjunctiva, eyelids, and nasal cavity;
  • African reed frogs: Rhinosporidium rwandae causes spherical skin nodules with a visible central black spot; composed of large intradermal thick-walled cysts with myriad 2–12 μm endospores

 

REFERENCES:  

1. Boes KM. Respiratory System. In: Raskin RE, Meyer DJ, eds. Canine and Feline Cytology: A Color Atlas and Interpretation Guide. 4th ed. St. Louis, MO: Elsevier; 2023:189, 192-193. 
2. Caswell JL, Williams KJ. Respiratory system. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 2. 6th ed. St. Louis, MO: Elsevier; 2016: 579-581.
3. Fenton K, McManamon R, Howerth EW. Anseriforms, ciconiiformes, charadriiformes, fruiformes. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Elsevier; 2018: 717.e5.
4. Greene CE. Rhinosporidiosis. In: Green CE ed., Infectious Diseases of the Dog and Cat. 4^th ed., St. Louis, MO: Elsevier Saunders; 2012: 702-704.
5. Lane LV, Yang PJ, Cowell RL. Selected Infectious Agents. In: Valenciano AC, Cowell RL, eds. Diagnostic Cytology and Hematology of the Dog and Cat. 5th ed. St. Louis, MO: Elsevier Mosby; 2014:52, 60. 
6. Lopez A, Martinson SA. Respiratory System, Thoracic Cavities, Mediastinum, and Pleurae. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 7th ed. St. Louis, MO: Elsevier; 2022:565-566; 603.
7. Pessier AP. Amphibia. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Elsevier; 2018: 946.
8. Wellman ML, Radin MJ. Nasal Exudates and Masses. In: Valenciano AC, Cowell RL, eds. Diagnostic Cytology and Hematology of the Dog and Cat. 5th ed. St. Louis, MO: Elsevier Mosby; 2020:126. 

 

 

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