JPC SYSTEMIC PATHOLOGY

RESPIRATORY SYSTEM

September 2023

P-F03

 

Signalment (JPC #2347944): A sea otter (Enhydra lutris)

 

HISTORY: This otter was found on the beach near San Diego, California; numerous white lesions throughout the lungs, liver, and kidney were found during necropsy. 

 

HISTOPATHOLOGIC DESCRIPTION: Lung: Affecting approximately 30% of the pulmonary parenchyma are multiple variably sized nodules of pyogranulomatous inflammation characterized by large numbers of viable and degenerate neutrophils and epithelioid macrophages admixed with fewer lymphocytes, plasma cells, and rare foreign body-type multinucleated giant cells. Inflammatory nodules are occasionally centered on individualized 30-80 µm diameter fungal spherules which have a 1-3 µm thick, double contoured, hyaline wall and are filled with granular to flocculent, basophilic material or occasionally few 2-5 µm, round, basophilic endospores. Inflammatory cells extend into surrounding alveoli, where they form an exudate admixed with flocculent eosinophilic edema fluid and increased numbers of alveolar macrophages. Alveolar septa are expanded up to 3 times normal by macrophages, fewer neutrophils, lymphocytes, fibrin, and edema. Multifocally, bronchiolar lumina contain a small amount of exudate composed of viable and degenerate neutrophils, macrophages, hemorrhage, fibrin, edema, and necrotic debris. There is multifocal, moderate anthracosilicosis.

   

MORPHOLOGIC DIAGNOSIS: Lung: Pneumonia, pyogranulomatous, multifocal, marked, with rare fungal spherules, sea otter (Enhydra lutris), mustelid.

 

ETIOLOGIC DIAGNOSIS: Pulmonary coccidioidomycosis 

 

CAUSE: Coccidioides immitis or C. posadasii

 

SYNONYMS: Valley fever, San Joaquin Valley fever

 

GENERAL DISCUSSION:  

• C. immitis (less often C. posadasii): Geophilic dimorphic fungus that can infect all mammals (including marine mammals)
• Primarily a respiratory disease; subsequent hematogenous dissemination from the lung to the heart and pericardium, central nervous system, eyes, skin, bone, liver, spleen, kidney, or testes
• Endemic in the Western Hemisphere; southwestern U.S., focal areas of Mexico, and Central and South America
• C. immitis is found almost exclusively in California, while the recently classified C. posadasii is considered the non-California species, endemic to the lower Sonoran life zone
• Differentiated from other dimorphic fungi by large size and endosporulation of mature sporules – similar to Rhinosporidium seeberi (aquatic protistan parasite)
• Laboratory personnel are at risk from aerosolized endospores; appropriate PPE should be used

 

PATHOGENESIS:  

• Inhalation of arthroconidia (environmental) > transition of arthroconidia into spherules (yeast) at body temperature, which are resistant to phagocytosis > endospores form within spherule (endosporulation) > endospores released, grow into 2^nd gen spherules and release more endospores                                                                                                              
  1. Hematogenous spread possible to other organs, or spread via infected macrophages (through leukocyte trafficking)
• Virulence factors include:

• Production of a spherule outer wall glycoprotein that modulates the immune response and compromises cell-mediated immunity
• Depletion of spherule outer wall glycoprotein on the surface of endospores which prevents their phagocytosis
• Production of host tissue arginase I and coccidioidal urease, which contribute to tissue damage at sites of infection

• Recovery requires cell mediated immunity; humoral response is common and serves as a marker for exposure or previous infection

 

LIFE CYCLE:  

 

TYPICAL CLINICAL FINDINGS:

• Non-specific: Persistent fever, shifting lameness, dyspnea, cough, peripheral lymphadenopathy, cutaneous nodules, cachexia and death        
• Many animals in endemic areas become infected without ever showing clinical signs of disease

 

TYPICAL GROSS FINDINGS:

• Lungs: Pyogranulomatous interstitial pneumonia; grey to white nodules with caseous or suppurative core
• Pulmonary lymph nodes: Multifocal to coalescing, gray-white thick-walled nodules, necrotic center 
• Systemic lesions possible in cases with hematogenous spread from lungs: tracheobronchial lymph node enlargement, nodular lesions in skin with draining tracts or abscesses, granulomatous lesions in pericardium or heart, brain, liver, spleen, kidney, testes, and osteomyelitis possible.

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:  

• Characteristic large size and endosporulation of the mature spherules: 20-200 µm diameter; double contour, refractile, hyaline wall; mature spherules contain myriad 2-5 µm endospores
• Size of the fungus varies with developmental stage: 

• Immature spherules (or sporangia): 10 - 20 µm in diameter, lack endospores
• Mature spherules: enlarge up to 200 µm in diameter, contain endospores
• Endospores: 2 - 5 µm in diameter

• Mature spherules elicit granulomatous or pyogranulomatous inflammation
• Endospores and arthroconidia usually elicit a more suppurative response

• CNS: Nodules with 1-2 spherules within zone of epithelioid macrophages
• Circulatory: Granulomatous lesions in pericardium or heart
• Skin: Pyogranulomatous dermatitis, fistulous tracts, pseudoepitheliomatous hyperplasia of overlying epidermis
• Eye: Granulomatous iritis, uveitis, or rarely chorioretinitis; may be uni- or bilateral
• Bone: Granulomatous osteomyelitis

 

ULTRASTRUCTURAL FINDINGS:

• Spherules: Cell wall, highly folded plasma membrane; occasional club-like projections radiate from the surface
• Cysts contain endospores with cleavage furrows and distinct nuclei

 

ADDITIONAL DIAGNOSTIC TESTS:

• Cytologic findings:
  1. Spherules: Blue, round, 10-200µm diameter, double walled containing finely granular protoplasm or can be folded/collapsed
  2. Endospores: Within spherules or phagocytosed by inflammatory cells; small, round to ovoid, 2-5µm diameter and contain a thin, clear cell wall, clear to light blue cytosol and dark blue, eccentric nuclei
• PAS (+): Endospores and immature spherules; PAS (-) cell wall
• GMS (+): Endospores, +/- wall 
• Complement fixation (titers of > 1:8 considered positive) 
• Gel diffusion precipitin test

 

DIFFERENTIAL DIAGNOSIS:  

Organisms that produce spherule-like structures: 

• Rhinosporidium seeberi (P-F01):  Sporangia up to 350 um diameter, 3-5 um thick wall and 6-10 um diameter endospores
• Emmonsia (formerly Chrysosporium) parva and E. crescens: Respiratory fungal infection of wild rodents, insectivores, herbivores, and carnivores; thick walled uninucleate adiaspores and fibrotic granulomas; no endospores; spherules 200-400 um diameter
• Blastomyces dermatitidis (P-F05, I-F06, S-F02): Similar in size to Cryptosporidium sp. immature spherules
• Prototheca sp. (D-F03, S-M03, U-M05)
• Chlorella sp. 

Dimorphic fungal infections:

• Blastomyces dermatitidis (P-F05, I-F06, S-F02)
• Cryptococcus neoformans (P-F04, I-F08, N-F02, S-F01)
• Histoplasma capsulatum (P-F02, D-F01, N-F01)
• Mucor amphibiorum, causative agent of disseminated mycosis in Australian anurans (amphibians)

Organisms that reproduce by endosporulation:

• Coccidioides immitis/C. posadasii
• Rhinosporidium seeberi (P-F01, main differential for coccidioidomycosis)
• Prototheca sp. (D-F03, S-M03, U-M05)
• Chlorella sp.
• Batrachochytrium dendrobatidis (I-F10)

 

COMPARATIVE PATHOLOGY:

• Disseminated form: Llamas and alpacas are particularly susceptible; most common in dogs, and occasionally in horses, sheep, cattle, cats, burros, and llamas
• Camelids: Probably the most important fungal disease in NW camelids

• Granulomas/granulomatous inflammation can coalesce and efface entire organs
• Vertical transmission documented

• Equidae, domestic and wild (Przewalski horses): Granulomas most commonly in lungs, liver, kidney, and spleen; recurring nasal granulomas; rarely abortions and mastitis 
• Cattle, pigs, sheep, goats: Granulomatous lesions primarily in the bronchial and mediastinal lymph nodes; spherules often surrounded by Splendore-Hoeppli material
• Cats: Lesions usually limited to skin, lungs, and associated lymph nodes; cutaneous nodular lesions are the most common presentation in cats 
• Dogs: Large granulomatous nodules composed of clusters of small granulomas separated by fibrous tissue
• Non-human primates (New World, Old World monkeys, and Great Apes): Increased occurrences when housed outdoors, lungs most often affected; chimpanzees can experience hypertrophic osteoarthropathy with disseminated infection
• Marine mammals (sea lions, sea otters, and dolphins): Pulmonary coccidioidomycosis common infection along central California coast; may find organisms in brain tissue with necrotizing encephalitis 
• Other wildlife case reports from species in endemic regions or captive species housed in endemic regions:

• Captive chimpanzees: Typical lesions occur, as well as hypertrophic osteopathy
• Coccidioides immitis-associated pneumonia reported in Sonoran gopher snake
• Black rhinoceros: Incidental finding of pulmonary and lymph node granulomas
• South American tapir: Pulmonary granuloma; uncommon in artiodactyls – chronic pyogranulomatous pneumonia
• Collared peccaries: Rarely develop clinical signs or lesions, Texan peccaries may experience apparent neurologic disorder without gross or microscopic brain lesions
• Captive ring-tailed lemur: Pulmonary and disseminated coccidioidomycosis with intralesional spherules
• Sea otters and river otters: Pyogranulomatous pleuropneumonia with pleural effusion, granulomatous lymphadenitis, encephalitis, dermatitis, peri- and myocarditis, ophthalmitis

 

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