Cryptococcosis

• Cause: cryptococcosis (Cryptococcus neoformans Cryptococcus neoformans - Cryptococcus gattii species complex) is caused by a dimorphic fungus that can grow as a mold in the environment and as a yeast at the higher temperatures within the tissues of infected hosts.
• There are 4 major molecular types of C. neoformans (VNI-VNIV) and C. gattii (VGI-VGIV), with subdivisions in VGII and III (VGIIa-c, VGIIIa-b).
• Differences in species and molecular type are associated with differences in clinical presentation.
• Organisms usually colonize the upper respiratory tract after inhalation of the infectious propagules known as basidiospores.
• Most common systemic fungal disease in cats (more common in cats than dogs).
• Signs: clinical presentation depends on the stage of disease at which diagnosis occurs, and is also influenced by host species and molecular type of the organism.
• In early disease upper respiratory signs predominate. Infection can remain localized within the sinonasal cavity or can extend to involve paranasal tissues including the CNS via breach of the cribiform plate (meningoencephalitis); along the optic nerve (optic neuritis/chorioretinitis); into the lower respiratory tract; or can disseminate hematogenously to any organ (eg lymph nodes, skin, CNS, abdominal organs). Once hematogenous spread occurs, multiple organs can be affected, especially the CNS.
• In dogs, dissemination of disease occurs early and presentation for CNS and/or ocular signs is common overall.
• Diagnosis: clinical signs and serology.
• Treatment: fluconazole, itraconazole, amphotericin B.
• Prognosis: poor overall compared to cats, and in addition to CNS involvement, is influenced by the cryptococcal strain and host immunity.

Presenting signs

• Fever is uncommon.
• Weight loss and lethargy is common in dogs.

Upper respiratory tract

• Chronic rhinitis with sneezing and nasal discharge. In more advanced disease there may be epistaxis and/or facial deformity, especially over nasal bridge. If caudal nasal cavity affected, presenting sign may be stertor only.

Ocular signs

• Sudden blindness.
• If ocular involvement, signs include anterior uveitis Uveitis , chorioretinitis Chorioretinitis , panophthalmitis and optic neuritis Optic neuritis. Other signs include ocular discharge, blepharospasm, aqueous flare, anterior chanber exudates, corneal opacities, pupillary abnormalities, retinal or optic disk infiltrates and blindness.

Neurological signs

• Decreased mentation/coma.
• Disorientation, behavior change, head pressing.
• Vestibular signs, eg head tilt, nystagmus, circling.
• Cranial nerve deficits.
• Gait abnormalities (ataxia, paresis).
• Facial twitching, muscle tremors, seizures,
• Cervical pain.

Lower respiratory tract

• More common in dogs than cats, other subclinical.
• Coughing and dyspnea.

Disseminated disease

• Cutaneous or mucosal lesions more common in cats than dogs.
• Pink, flesh cutaneous nodules especially head, trunk, digits or neck.
• Palate, tongue and lips can be affected.
• Draining wounds/sinus tracts or ulcers may be present.
• Vomiting or palpable mass lesions if abdominal involvement.
• Lymph node involevment.
• Musculoskeletal involvement uncommon (joints, bones).

Geographic incidence

• These saprophytic yeasts are widely distributed in nature. C. neoformans is globally endemic; weathered pigeon excreta are the most frequently reported source, decaying vegetation is a less common source.
• The distribution of C. gattii has expanded from tropical and subtropical climatic regions to include many other regions around the world, especially the North West Pacific Rim including British Columbia and California; environmental sources include tree bark and decaying vegetation. It has also been isolated from air and water.
• Since C. gattii can be found in air and water indoor pets are also at rsk of infection.

Age predisposition

• Young dogs are most commonly affected and usually less than 5 y of age.

Breed/Species predisposition

• Doberman Pinshers Dobermann and Great Danes Great Dane in Australia are at increased risk.
• Cocker Spaniels American Cocker Spaniel are at higher risk in North America.

Public health considerations

• Contact with infected animals is not a concern since the organism does not aerosolize from tissue sites.
  Caution should be used with immunocompromised individuals when affected animals have draining nodules.
• Cultures are also not a concern because the yeast form is detected and it does not aerosolize.