NAVLE Respiratory

Feline Cryptococcosis and Other Fungal Respiratory Diseases – NAVLE Study Guide

March 28, 2026 25 min read 25 views
Fungal respiratory diseases represent an important category of infectious disease in cats, with cryptococcosis being the most common systemic mycosis of cats worldwide.

Overview and Clinical Importance

Fungal respiratory diseases represent an important category of infectious disease in cats, with cryptococcosis being the most common systemic mycosis of cats worldwide. Understanding the clinical presentations, diagnostic approaches, and treatment protocols for these infections is essential for the NAVLE examination and clinical practice.

This study guide covers the major fungal pathogens affecting the feline respiratory system, including Cryptococcus, Histoplasma, Blastomyces, Coccidioides, Aspergillus, and Sporothrix species. Each organism has unique geographic distribution, clinical presentations, and treatment considerations that are frequently tested on board examinations.

Clinical Form Clinical Signs Frequency/Notes
Nasal (Most Common) Chronic nasal discharge (unilateral or bilateral), sneezing, stertor, nasal deformity, polyp-like mass in nostril, submandibular lymphadenopathy 56-83% of cases; firm swelling over bridge of nose in approximately 70% of cases
Cutaneous Papules, nodules (1-10 mm), ulcerated lesions, draining tracts, subcutaneous swelling Approximately 40% of cases; may occur alone or with other forms
CNS Obtundation, behavioral changes, seizures, vestibular signs (head tilt, nystagmus), ataxia, paresis, mydriasis, blindness, facial twitching May derive from nasal form via cribriform plate; carries guarded prognosis
Lower Respiratory Dyspnea, tachypnea, cough (rare), pulmonary masses, pleural effusion, mediastinal mass Less common than nasal form; may indicate disseminated disease
Ocular Granulomatous chorioretinitis, anterior uveitis, exudative retinal detachment, blindness, panophthalmitis Often associated with CNS disease; infection may track along optic nerve

Cryptococcosis

Etiology and Epidemiology

Cryptococcus neoformans and Cryptococcus gattii are the primary species causing feline cryptococcosis. These are encapsulated basidiomycetous yeasts that infect cats following inhalation of basidiospores from the environment. The polysaccharide capsule is the major virulence factor, inhibiting phagocytosis and providing protection against host immune defenses.

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