JPC SYSTEMIC PATHOLOGY

URINARY SYSTEM

December 2023

U-M25

 

Signalment (JPC # 1535323): 6-year-old spayed female Doberman pinscher

 

HISTORY: Presented with idiopathic bilateral conjunctivitis. Various treatments were ineffective.

 

HISTOPATHOLOGIC DESCRIPTION: Kidney: Multifocally affecting 40% of this section, the cortical interstitium is markedly expanded, and tubules are effaced by numerous plasma cells, fewer lymphocytes, and macrophages admixed with fibrous connective tissue, hemorrhage, fibrin, edema, and many 5‑20 mm diameter, round to oval, thin‑walled sporangia with flocculent amphophilic centers that contain 2 to 4 distinct, basophilic, 3-4 mm diameter, pie wedge‑shaped endospores, surrounded by a clear halo (algal organisms). Within affected areas, glomeruli have one or more of the following changes: periglomerular fibrosis, hypertrophic parietal epithelium, mildly dilated uriniferous spaces, shrunken, hypocellular tufts with loss of capillary lumens (sclerosis), and/or segmental tuft necrosis. Multifocally, tubules are often either degenerate with swollen vacuolated cytoplasm, or necrotic with shrunken hypereosinophilic cytoplasm and pyknotic nuclei and sloughed into the lumen (cellular casts). There is diffuse fibrosis of the renal crest which replaces collecting ducts along with additional lymphocytes, plasma cells, and fewer macrophages. Multifocally, the capsule is moderately thickened.

 

M25b: Kidney (PAS): Within the cortical areas of tubular loss, the organisms are PAS positive with the following forms: intact uninucleate organisms; multiple endospores with internal septation within sporangia; and collapsed, folded, empty cell walls.

 

M25c: Kidney (GMS): Organisms are argyrophilic with the following forms: intact uninucleated organisms; multiple endospores with internal septation within sporangia; and collapsed, folded, empty cell walls.

 

MORPHOLOGIC DIAGNOSIS: Kidney: Nephritis, interstitial, lymphoplasmacytic, multifocal, marked, with fibrosis, glomerulosclerosis, tubular degeneration and necrosis, and numerous algal sporangia, Doberman pinscher, canine.

 

ETIOLOGIC DIAGNOSIS: Renal protothecosis

 

CAUSE: Prototheca spp.

 

GENERAL DISCUSSION:

• An opportunistic, colorless, unicellular alga, considered a mutant achlorophyllous form of Chlorella (green algae); ubiquitous in some niche areas such as raw and treated sewage, fresh and marine water, feces, plant sap, tree slime and occasionally as contaminants of various substrates including cow’s milk 
• P. zopfii and P. wickerhamii are most common with mastitis in cows and disseminated disease in dogs being most common manifestations
• Reproduction is asexual via endosporulation
  1. Species-specific sites: Mammary gland in cows, gastrointestinal tract and disseminated in dogs, skin in cats and humans
• Dogs:
  1. Two forms: 
     • Disseminated with ocular (only in dog), CNS, bone, kidneys, myocardium and gastrointestinal (more common) involvement; prognosis is poor following dissemination
     • Cutaneous (rare)
  2. Collies and boxers are overrepresented; immunosuppression may contribute
• Cattle, horses, and wild pigs pass Prototheca spp. in the feces without clinical disease 

 

PATHOGENESIS:

• Not completely understood
• Gains access through traumatic inoculation in cutaneous infections, invasion of the teat canal in cows, and through the colon in dogs (potentially through existing lesions) > depressed cell-mediated immunity, in the dog, allows opportunistic invasion and circulatory dissemination

 

TYPICAL CLINICAL FINDINGS:

 

TYPICAL GROSS FINDINGS:

• Eye: Exudate in anterior chamber; gray-white granular material filling vitreous cavity
• Intestine: Small, white to grey serosal nodules; friable, thickened corrugated colon/rectum; patchy, hemorrhagic, necrotizing and ulcerative enterocolitis
• Kidney: Disseminated white to gray nodules or depressions on the surface, with grey, white, or tan foci within the parenchyma and at the corticomedullary junction; necrosis of the renal papillae
  1. P. zopfii organisms have been identified in glomerular capillaries, interstitial granulomas, and urine 
• Mesenteric lymph nodes: Enlarged and pale
• Myocardium: Multifocal pale streaks
• Serosal surfaces (peritoneum, heart, liver, spleen, lymph nodes): Disseminated gray foci
• Skin: Papules and nodules, often over pressure points or ulcerations involving mucocutaneous junctions (especially nostrils), scrotum, and paw pads

 

TYPICAL CYTOLOGY FINDINGS:

• Granulomatous or pyogranulomatous inflammation
• Epithelioid macrophages predominate, but lymphocytes, plasma cells, and occasional multinucleated giant cells
• Sporangia and endospores may be extracellular or intrahistiocytic
• Sporangia are 5-20 mm in diameter, round to oval, with internal septations producing 2-20 endospores within the cell wall
• Endospores are basophilic and granular, with a single nucleus. Endospores have a clear surrounding halo

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:

• Granulomatous to pyogranulomatous ulcerative colitis; intracellular and extracellular algal organisms
• Granulomas in various organs with disseminated disease
• Algal organisms: unicellular, nonbudding, round to oval spherules with refractile capsule; 5-12 µm (P. wickerhamii) to 10-25 µm (P. zopfii); radially arranged wedge-shaped endospores within a single sporangium
• Organisms may be found in many organs and cerebrospinal fluid but stain lightly on H&E
• Numerous organisms are both free within the tissue and within macrophages; minimal necrosis
• Kidney: Lymphoplasmacytic to granulomatous nephritis; organisms are likely embolic and have been identified in glomerular capillaries, interstitial granulomas, and in urine
• Eye: Bilateral and can vary from lymphoplasmacytic to granulomatous panuveitis with optic neuritis and exudative retinal separation
• Skin: Granulomatous to pyogranulomatous dermatitis and panniculitis

 

ULTRASTRUCTURAL FINDINGS:

• “Mercedes-Benz” endospores – tripartite cell wall division
• Prototheca spp:
  1. Central nucleus, large nucleolus
  2. Thick granular cell wall
  3. Electron dense bodies in cytoplasm
  4. Starch granules

 

ADDITIONAL DIAGNOSTIC TESTS:

• Culture 
• GMS, PAS, Gridley (GF)
• FA techniques (species-specific)
• PCR targeting D1/D2 portion of the 28S rRNA (large ribosomal subunit) has successfully identified Prototheca sp. (Falcaro, J Vet Diagn Invest, 2020)
• CSF cytology: Marked eosinophilic pleocytosis and Prototheca organisms (Asiag, J Vet Diagn Invest 2020)

 

DIFFERENTIAL DIAGNOSIS (Organisms that reproduce by endosporulation):

• Chlorella spp.: Photosynthetic algal organism reported in cattle, sheep, gazelle and beaver; granulomatous and necrotizing lesions with similar organisms containing intracytoplasmic starch granules which are PAS positive-diastase sensitive, anisotropic in unstained and H & E sections and with chloroplasts are evident on EM; green discoloration of unfixed tissue grossly
• Coccidioides immitis: Larger (10‑60 mm), with many endospores per sporangium
• Rhinosporidium seeberi: Large, distinctive organisms in nasal mucosa
• Chytridiomycosis (Batrachochytrium dendrobatidis): Amphibian disease that incites hyperplastic and hyperkeratotic epithelial lesions

 

COMPARATIVE PATHOLOGY:

• Cat: Cutaneous form caused by P. wickerhamii is most common but nasal dermatitis from P. zopfii has been identified
• Bovine: Cystic granulomatous mastitis with eosinophils and multinucleated giant cells, granulomatous lymphadenitis and peritonitis, enteritis
• Salmon: Granulomatous nephritis
• Deer: Pustular dermatitis
• Goat: Ulcerative and granulomatous dermatitis
• Horses: Rare cutaneous reports; capable of causing upper respiratory tract infection (Schoniger, J Comp Pathol, 2016)
• Bat: Granulomatous/histiocytic inflammation and organisms consistent with Prototheca sp. were identified in the lymph nodes, spleen, meninges/brain, mesentery, pancreas, heart, skeletal muscle, and kidney of a captive Pteropus lylei. 

 

REFERENCES:

1. Asiag N, Lapid R, Aizenberg Z, et al. Spinal cord protothecosis causing paraparesis in a dog. J Vet Diagn Invest. 2022;34(4):684-688.
2. Boes KM. Respiratory system. In Raskin, RE, Meyer, DJ, Boes KM eds. Canine and feline cytopathology. St. Louis, MO: Elsevier; 2023:191.
3. Ciancioli RE, Mohr FC.  Urinary system. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 2, 6th ed. St. Louis, MO: Elsevier; 2016:433.
4. Conrado FO. Fecal and rectal cytopathology. In Raskin, RE, Meyer, DJ, Boes KM eds. Canine and feline cytopathology. St. Louis, MO: Elsevier; 2023:392-393.
5. Deshuillers PL, Raskin RE. Eyes and ears. In Raskin, RE, Meyer, DJ, Boes KM eds. Canine and feline cytopathology. St. Louis, MO: Elsevier; 2023:579.
6. Falcaro C, Furlanello T, Binanti D, et al. Molecular characterization of Prototheca in 11 symptompatic dogs. J Vet Diag Invest. 2021;33(1):156-161.
7. Farina LL, Lankton JS. Chiroptera. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Elsevier. 2018:626.e3.
8. Fidelis CE, Franke M, de Abreu LCR, Jagielski T, Ribeiro MG, Dos Santos MV, Gonçalves JL. MALDI-TOF MS identification of Prototheca algae associated with bovine mastitis. J Vet Diagn Invest. 2021;33(2):1168-1171.
9. Fisher DJ. Cutaneous and Subcutaneous Lesions. In: Valenciano AC, Cowell RL, eds. Diagnostic Cytology and Hematology of the Dog and Cat. 5th ed. St. Louis, MO: Elsevier Mosby; 2014:83. 
10. Haddad JL, Marks Stowe DA, Neel JA. The Gastrointestinal Tract. In: Valenciano AC, Cowell RL, eds. Diagnostic Cytology and Hematology of the Dog and Cat. 5th ed. St. Louis, MO: Elsevier Mosby; 2014:294, 315. 
11. Hostetter SJ. Oral cavity, gastrointestinal tract, and associated structures. In Raskin, RE, Meyer, DJ, Boes KM eds. Canine and feline cytopathology. St. Louis, MO: Elsevier; 2023:316-317.
12. 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; 2014:53, 61. 
13. 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; 2022:631.
14. Mauldin EA, Peters-Kennedy J.  Integumentary system. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 1, 6th ed. St. Louis, MO: Elsevier; 2016:665-666.
15. Raskin RE, Conrado FO. Integumentary system. In Raskin, RE, Meyer, DJ, Boes KM eds. Canine and feline cytopathology. St. Louis, MO: Elsevier; 2023:57-58.
16. Riet-Correa F, Carmo PMSD, Uzal FA. Protothecosis and chlorellosis in sheep and goats: a review. J Vet Diagn Invest. 2021;33(2):283-387.
17. Spagnoli ST, Gelberg HB. Alimentary System and the Peritoneum, Omentum, Mesentery, and Peritoneal Cavity. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 7th ed. St. Louis, MO: Elsevier; 2022:454. 
18. Wilcock BP, Njaa BL.  Special senses. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 1, 6th ed. St. Louis, MO: Elsevier; 2016:451.

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