JPC SYSTEMIC PATHOLOGY

RESPIRATORY SYSTEM

September 2023

P-F04 (NP)

 

Signalment (JPC #1804208): Pacific white-sided dolphin (Lagenorhynchus obliquidens)

 

HISTORY: Unknown

 

HISTOPATHOLOGIC DESCRIPTION: SLIDE A: Lung: Diffusely, bronchial, bronchiolar, and alveolar lumina and occasionally alveolar septa are filled or expanded by numerous extracellular and intrahistiocytic, spherical, 8-20 µm diameter yeast that have a pale, amphophilic center, a thin, refractile wall, are surrounded by a clear, 5 µm wide, non-staining capsule, and occasionally exhibit narrow based budding. Approximately 20% of alveolar, bronchiolar, and bronchial lumina are filled with an exudate composed of numerous macrophages, viable and degenerate neutrophils, fewer lymphocytes and plasma cells, occasional multinucleated giant cells, and variable amounts of hemorrhage, fibrin, and edema. Alveolar septa are often expanded up to 3-5 times normal by macrophages, lymphocytes, plasma cells, and few neutrophils and eosinophils, as well as hemorrhage, fibrin, edema, and congestion. There is multifocal necrosis of alveolar septa, bronchioles, and bronchi characterized by loss of cellular architecture and replacement by eosinophilic cellular and karyorrhectic debris. Rarely, bronchial and bronchiolar epithelium is attenuated.  

 

SLIDE B: Mucicarmine stain: Diffusely, there is bright red staining of yeast capsules (carminophilia), and yeast occasionally exhibit narrow based budding.

 

MORPHOLOGIC DIAGNOSIS: Lung: Pneumonia, pyogranulomatous, diffuse, marked, with numerous carminophilic yeast, Pacific white-sided dolphin (Lagenorhynchus obliquidens), cetacean. 

 

ETIOLOGIC DIAGNOSIS: Pulmonary cryptococcosis

 

CAUSE: Cryptococcus neoformans  

 

SYNONYM: European Blastomycosis; Torulosis; Busse-Buschke’s disease

 

GENERAL DISCUSSION:

• Saprophytic yeast with worldwide distribution; infections in humans and a wide variety of domestic, wild and laboratory animals  
• Cryptococcosis is the most common systemic mycotic disease of cats  
• The most common pathogenic species are Cryptococcus neoformans, found in soil and pigeon or other avian guanos, and decaying organic matter, and Cryptococcus gattii (formerly C. neoformans var. gattii), found primarily in organic material (particularly tropical plants)
• Infection may be localized or disseminated with a predilection for the respiratory (particularly the nasal cavity) and central nervous systems  
• The only pathogenic fungus that secretes a mucopolysaccharide capsule

 

PATHOGENESIS:

• The mode of transmission unproven; the most likely route of entry is via inhalation of contaminated dust > primary infection in the nasal cavity, upper respiratory tract, sinuses, or oropharynx  > spread to lungs via aspiration > secondary hematogenous spread to the CNS, eyes, skin, and other organs
• The necessity for predisposing immunosuppression or debilitation is less clear in animals; debilitation appears to be a consequence of rather than a contributing factor to cryptococcal infection
• Four virulence factors:
  • Mucopolysaccharide capsule prevents phagocytosis by alveolar macrophages, impairs phagocytosis and leukocyte migration, activates complement and may suppress T-cell responses; acapsular strains are less virulent
  • Melanin, a powerful antioxidant, reduces the toxicity of hydroxyl radicals, superoxides, and singlet oxygen radicals found within the phagolysosome; melanin is produced from phenols by phenol oxidase via the laccase pathway
  • Enzyme production
    • Phospholipase injures alveolar type II epithelial cells and hinders production and function of surfactant – increasing adhesion to pneumocytes.
    • Urease facilitates blood-to-brain invasion by enhancing yeast sequestration within microcapillary beds and promotes immature dendritic cells and a non-protective Th2 immune response within the lung (Osterholzer, 2009)
    • Proteases: Metabolize host immunoglobulins and complement proteins
  • Sialic acids found in the cell wall direct complement proteins toward the degradative processes rather than generating opsonizing fragments and anaphylatoxins

• Infection in marine mammals is thought to be spread by contact with seabird guano (Cryptococcus neoformans) or contact with eucalyptus trees growing near the shore (Cryptococcus gattii)

 

TYPICAL CLINICAL FINDINGS:

• Respiratory: Chronic unilateral or bilateral rhinitis with sneezing and mucopurulent nasal discharge, firm to fluctuant swelling over bridge of nose
• CNS (N-F02): Vestibular signs, ataxia, nystagmus, paresis/paralysis, seizures, hyperesthesia, head pressing, blindness, anosmia 
• Ocular (S-F01): Granulomatous chorioretinitis with progression to posterior synechiae, optic neuritis, panophthalmitis, retinal detachment and retinal hemorrhage
• Cutaneous (I-F08): Firm to fluctuant papules and nodules typically on head and face; often ulcerative with serous exudation; associated lymphadenopathy

 

TYPICAL GROSS FINDINGS:

• Discrete, white, gelatinous, granulomatous, or nodular lesions that may project from or displace the affected organ.
• Gelatinous lesions in brain or spinal cord (cryptococcoma or toruloma) that must be differentiated from oligodendrogliomas
• Tracheobronchial LNs can be enlarged and reactive, generalized lymphadenomegaly is uncommon
• Systemic dissemination: Nasal mucosal mucinous lesions, pulmonary abscesses, jejunal granulomas, mastitis, lymphadenitis, and placentitis with abortion and infection of the fetus

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:

• Spherical, 4-15 µm diameter yeast surrounded by a 8-40 µm thick, mucopolysaccharide capsule; characteristic soap bubble appearance because of the capsule
• Reproduces by single, narrow-based buds
• Unlike other fungal infections, a profound cellular inflammatory reaction is not typical; infection in dogs often elicits a granulomatous response
• Uncommon strains of Cryptococcus sp. lack a capsule (acapsular), resulting in a robust granulomatous response; yeasts are easily phagocytosed; narrow based budding is consistent
• Lesions appear as multifocal areas of necrosis with granulomatous or pyogranulomatous inflammation with few fungal spherules (discrete granulomas are infrequent)

 

ADDITIONAL DIAGNOSTIC TESTS:  

• Fungal culture
• Capsule stains positively with Mayer’s mucicarmine or Alcian blue; the organism itself stains with PAS or GMS.
• Serology:   ELISA, FA, LCAT (latex cryptococcal agglutination test) 
• Cytology:   

• Romanowsky stains: Capsule typically remains unstained, leading to a soap-bubble appearance
• India ink/New methylene blue: Provide negative relief to highlight non-staining capsule
• Mucicarmine: The capsule is carminophilic

• PCR: Detection of CAP59 gene

 

DIFFERENTIAL DIAGNOSIS:

• Blastomyces dermatitidis (P-F05): Unencapsulated, 8-25 µm diameter, round yeast; broad based budding; difficult to differentiate from large, acapsular forms of Cryptococcus
• Coccidioides immitis (P-F03): Unencapsulated, larger (5-100 µm diameter) fungal spherule; reproduces by endosporulation rather than budding
• Histoplasma capsulatum (P-F02): Small, 2-6 µm diameter, irregularly oval, intrahistiocytic yeast

(See table below.)

 

COMPARATIVE PATHOLOGY:

• Occurs worldwide in many species; cats most common species affected
• Dogs: Primarily young dogs which typically present with CNS and disseminated disease 
• Cattle: A cause of bovine mastitis (ascending infection via teat canal)
• Goats: Recent case report of pulmonary and encephalitis cryptococcosis in a nanny-goat in Brazil (Headley, J Vet Diag Invest 2018)
• Laboratory animals: Cryptococcus neoformans has been reported to affect immunocompetent laboratory mice and guinea pigs
• NHPs: Infects various species and presents with varying clinical symptoms due to disseminated nature of the infection and the multitude of organs that can be infected 
• Wildlife affected: 

• Cervidae (white-tailed deer, elk) 
• Felidae (cheetah) 
• New World and Old World Monkeys (various) (Mota et al., JCP 2021)
• Apes (various) 
• Monotremes and Marsupials (koalas) 
• Rodentia (slender-tailed cloud rat) 
• Cetacea (harbor porpoise, Dall’s porpoise, white sided dolphin, others) 
• Avians (North Island brown kiwi) 

Organism	Cryptococcus neoformans	Histoplasma capsulatum var. capsulatum	Coccidioides immitis	Blastomyces dermatiditis
Tissue response	Histiocytic; may be minimal	Pyogranulomatous	Pyogranulomatous	Pyogranulomatous
Diameter (µm)	4-15	2-6	5-100	8-25
Location	Extracellular, rarely intracellular	Intracellular	Intra- or Extracellular	Intra- or Extracellular
Cell wall thickness	Thin	Thin	Thick	Thick
Number of nuclei	Single	Single	None	Multiple
Budding and attachment	Single bud; narrow-based	Single bud; narrow-based	None	Single-bud; broad-based
Capsule	Mucicarmine-positive	None	None	None
Endospores	None	None	Yes	None
Dimorphic	Yes	Yes	Yes	Yes
Common species affected	Cats	Dogs, cats	Many species	Dogs
Common sites affected	Lung, CNS	Lung, disseminated	Lung	Lung, skin, disseminated

Modified from Migaki G, Hubbard GB, Butler TM. Histoplasma capsulatum var. duboisii Infection, Baboon. In: Jones TC, Mohr U, Hunt RD, eds. Nonhuman Primates II: Monographs on Pathology of Laboratory Animals.  New York, NY:Springer-Verlag;1993:21

 

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