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Fungal Disease - Cryptococcosis

Introduction

Cryptococcosis occurs when inhaled organisms establish an infection in the nasal cavity, paranasal sinuses, or lungs. Dissemination to skin, eyes, CNS, and other organs may follow. Cryptococcosis is uncommon in cats. It is rare in dogs, with highest incidences reported in young adults.

Etiology

Cryptococcus neoformans is an environmental saprophytic fungus that can be found worldwide.

Cats

The upper respiratory tract is most commonly involved, with sneezing, snuffling, nasal discharge, nasal mass, or a firm, subcutaneous swelling over the bridge of the nose.

Skin involvement is characterized by multiple non painful papules and nodules that may ulcerate.

Regional lymph adenomegaly is common. Signs of CNS (variable neurologic signs) and ocular disease (fixed, dilated pupils; blindness) are also often seen.

Dogs

This is usually a neurologic or ophthalmic disease in dogs. The upper respiratory tract is also frequently involved.

Occasionally, cutaneous ulcers occur, especially on the nose and lips, in the oral cavity, or around nail beds.

Differential diagnosis

Differentials include other fungal and bacterial infections and neoplasia.

Diagnosis

Cytology (exudate, tissue aspirates): (pyo)granulomatous inflammation with narrow, budding, thinwalled yeasts surrounded by variably sized, clear, refractile capsules.

Dermatohistopathology: nodular to diffuse (pyo) granulomatous dermatitis and panniculitis, with numerous organisms or vacuolated-appearing dermis and subcutis caused by large numbers of organisms.

ELISA or latex agglutination testing: detection of serum cryptococcal capsular antigen. In localized infections, test results may be negative.

Fungal culture: C. neoformans.

PCR analysis, where available, may simplify the diagnosis.

Treatment

Cutaneous lesions should be surgically excised, if possible.

Systemic antifungal therapy should be administered over the long term (several months) and continued at least 1 month beyond complete clinical resolution. Treatment should also be continued until follow-up serum cryptococcal antigen titers are negative.

Effective drugs include the following:

  • » Itraconazole (Sporanox) 5–10 mg/kg PO should be administered with food every 12 to 24 hours.
  • » Fluconazole 5–15 mg/kg PO should be administered every 12 to 24 hours.
  • » Ketoconazole 5–10 mg/kg PO with food q 12–24 hours
  • » Terbinafine 30–40 mg/kg PO q 24 hours
  • » Amphotericin B 0.5–0.8 mg/kg (added to 0.45% saline/2.5% dextrose, 400 mL for cats, 500 mL for dogs 20 kg and 1000 mL for dogs 20 kg) SQ two to three times per week until a cumulative dose of 8–26 mg/kg is administered. Concentrations of amphotericin B 20 mg/L may cause local irritation.

Prognosis: for cat is fair to good unless the CNS is involved. The prognosis for cats with CNS involvement and for dogs in general is poor. Infected animals and cultures are not considered contagious to other animals or to humans.


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