JPC SYSTEMIC PATHOLOGY

RESPIRATORY SYSTEM

September 2017

P-F04

 

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

HISTORY:  Unknown

HISTOPATHOLOGIC DESCRIPTION:  Lung:  Diffusely, bronchial, bronchiolar, and alveolar lumina and occasionally alveolar septa are filled or expanded by numerous extracellular and intrahistiocytic, spherical, 8-20 um diameter yeast that have a pale, amphophilic center, a thin, refractile wall, are surrounded by a clear, 5 um 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 cell macrophages, 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.  

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, etiology consistent with Cryptococcus neoformans, Pacific white-sided dolphin (Lagenorhynchus obliquidens), cetacean.

ETIOLOGIC DIAGNOSIS:  Pulmonary cryptococcosis

CAUSE:   Cryptococcus neoformans 

SYNONYM:  European Blastomycosis

GENERAL DISCUSSION:

• Saprophytic yeast with worldwide distribution; infections in humans and a wide variety of domestic, wild and laboratory animals
• 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 Cryptococcus gattii (formerly neoformans var. gattii), found primarily in organic material associated with eucalyptus trees
• 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
• 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
  • Phenoloxidase (laccase) protects organism from oxidative damage by producing melanin-like compound with antioxidant properties
  • Serine protease cleaves fibronectin and other basement membrane proteins and may aid in tissue invasion
  • 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
• 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 nasal discharge, firm to fluctuant swelling over bridge of nose
• CNS: Vestibular signs, ataxia, nystagmus, paresis/paralysis, seizures, hyperesthesia, head pressing, blindness, anosmia
• Ocular: Granulomatous chorioretinitis with progression to posterior synechiae, optic neuritis, panophthalmitis, retinal detachment and retinal hemorrhage
• Cutaneous: 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
• Generalized lymphadenomegaly with a gelatinous appearance
• 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, 2-10 um diameter yeast surrounded by a 1-30 um 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

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, India ink, mucicarmine
• PCR: Detection of CAP59 gene

DIFFERENTIAL DIAGNOSIS:

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

COMPARATIVE PATHOLOGY:

• Occurs worldwide in many species; cats most common species affected
• Dogs: Primarily young dogs which typically present with CNS and disseminated disease
• 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
• A cause of bovine mastitis (ascending infection via teat canal)
• Rabbits: Normally highly resistant to infection with neoformans; occasional animal model
• Koalas: Cryptococcus gattii associated with eucalyptus trees frequently becomes part of the normal sinonasal flora and often causes self-limiting, subclinical disease; recent single case report of unilateral exophthalmos caused by neoformans
• Single case reports of pulmonary infection in a free-living toad and disseminated Cryptococcosis in a red-tailed guenon (Cercopithecus ascanius)

 

Organism	Cryptococcus neoformans	Histoplasma capsulatum var. capsulatum	Coccidioides immitis	Blastomyces dermatiditis
Tissue response	Histiocytic; may be minimal	Histiocytic	Pyogranulomatous	Pyogranulomatous
Diameter (µm)	2-10	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

REFERENCES:

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8. Martinez-Nevado E, et al. Atypical presentation of Cryptococcus neoformans in koala (Phascolarctos cinereus): A magnetic resonance imaging and computed tomography study. J Zoo Wildl Med. 2017; 48(1):250-254.
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11. Miller WG, Padhye AA, Van Bonn W, Jensen E, Brandt ME, Ridgway SH. Cryptococcosis in a bottlenose dolphin (Tursiops truncates) caused by Cryptococcus neoformans var. gattii. J Clin Micro. 2002; 40:721-724.
12. Osterholzer JJ, Surana R, Milam JE, et al. Cryptococcal urease promotes the accumulation of immature dendritic cells and a non-protective T2 immune response within the lung. Am J Pathol. 2009; 174:932-943.
13. Rommel S, Lowenstine L. Gross and microscopic anatomy. In: Dierauf LA, Gulland FMD, eds. CRC Handbook of Marine Mammal Medicine. 2nd ed. Washington, D.C.: CRC Press; 2001:144.
14. Trivedi SR, Sykes JE, Cannon MS. Clinical features and epidemiology of cryptococcosis in cats and dogs in California: 93 cases (1988–2010). J AmVet Med Assoc. 2011;239(3):357-369.
15. Seixas F, Martins ML, Pinto ML, et al. A case of pulmonary cryptococcosis in a free-living toad (Bufo bufo). J Wildl Dis. 2008;44:460-463.
16. Szymczak WA, Sellers RS, Pirofski LA. IL-23 dampens the allergic response to Cryptococcus neoformans through IL-17-independent and -dependent mechanisms.

    Am J Pathol. 2012;180(4):1547-1559.

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