Cryptococcosis - Generalized Conditions - Merck Veterinary Manual (1)

Overview of Cryptococcosis

  • Cryptococcosis is a systemic fungal infection primarily caused by two species:

    • Cryptococcus neoformans

    • C. gattii

  • It may affect various body systems including:

    • Respiratory tract (primarily nasal cavity)

    • Central Nervous System (CNS)

    • Eyes

    • Skin (especially on the face and neck of cats)

Etiology and Transmission

  • Pathogen Distribution:

    • Fungi are found in soil and bird manure, notably pigeon droppings.

  • Infection Process:

    • Occurs worldwide through inhalation of fungal spores or via contaminated wounds.

  • Non-capsulated Form:

    • In avian droppings, may exist as small as 1 μm, enabling deep lung inhalation.

  • Species Affected:

    • Primarily affects cats; also seen in dogs, cattle, horses, sheep, goats, birds, and wild animals.

    • Human infections often linked to compromised immune systems.

Clinical Findings and Lesions

In Bovine

  • Associated with mastitis; presents with:

    • Anorexia

    • Decreased milk flow

    • Swelling in affected quarters

    • Enlarged supramammary lymph nodes

  • Milk may appear viscid, mucoid, or gray-white, and can also be watery with flakes.

In Equine

  • Almost exclusively presents as a respiratory illness.

  • Typical findings include obstructive growths in nasal cavities.

In Feline

  • Upper respiratory signs from nasal infection, including:

    • Sneezing

    • Discharge: mucopurulent, serous, or hemorrhagic (unilateral or bilateral)

    • Polyp-like masses in nostrils

    • Firm swelling on the nose bridge

  • Common cutaneous lesions:

    • Papules and nodules (fluctuant to firm)

    • Larger lesions may ulcerate.

  • Neurological signs:

    • Depression, seizures, changes in behavior, circling, paresis, and blindness.

  • Ocular signs:

    • Dilated pupils, retinal detachment, and optic neuritis.

In Canine

  • Frequently exhibits disseminated disease with CNS or ocular involvement.

  • Symptoms related to:

    • Meningoencephalitis

    • Optic neuritis

    • Granulomatous chorioretinitis

  • Respiratory tract lesions reported but are not usually the main presentation.

  • Lesions commonly occur in multiple organs:

    • Kidneys, lymph nodes, spleen, liver, thyroid, and others.

  • Lesion characteristics:

    • Gelatinous masses or granulomas, aggregates of organisms with minimal inflammation.

Diagnosis

  • Cytological evaluation is the quickest method of diagnosis, analyzing:

    • Nasal exudate

    • Skin exudate

    • Cerebrospinal fluid (CSF)

    • Aqueous or vitreous samples from the eye

    • Impression smears from lesions.

  • General Staining Techniques:

    • Gram stain: organism retains crystal violet; capsule lightly stains with safranin.

    • India ink: highlights the organism against a black background but is less definitive.

    • Wright stain: commonly used but can distort the organism; alternatives include new methylene blue and PAS stains.

    • Best for capsule visualization: Mayer mucicarmine.

  • Additional Diagnostic Tests:

    • Detection of cryptococcal capsular antigen in serum, urine, or CSF via latex agglutination test.

    • Organism culture from various bodily fluids and tissues, using Sabouraud agar.

Treatment

  • First-line Antifungal Treatments:

    • Fluconazole: 2.5–10 mg/kg/day

    • Itraconazole: 10 mg/kg/day

  • Amphotericin B:

    • Administered SC (0.5–0.8 mg/kg diluted in saline containing dextrose)

    • Given 2-3 times weekly

    • Lipid complex formulation available (1–2 mg/kg for cats and 2–3 mg/kg for dogs).

  • Flucytosine:

    • Can be used alone, usually in combination with amphotericin to mitigate drug resistance.