Cryptococcosis in cats: ABCD guidelines on prevention and management

Abstract

Overview: Cryptococcosis is worldwide the most common systemic fungal disease in cats; it is caused by the Cryptococcus neoformans- Cryptococcus gattii species complex, which includes eight genotypes and some subtypes (strains) with varying geographical distribution, pathogenicity and antimicrobial susceptibility. Cats acquire the infection from a contaminated environment. The prognosis is favourable in most cases, provided a diagnosis is obtained sufficiently early and prolonged treatment is maintained.

Infection: Basidiospores are the infectious propagules of Cryptococcus species as they penetrate the respiratory system and induce primary infection. Asymptomatic colonisation of the respiratory tract is more common than clinical disease. Avian guanos, particularly pigeon droppings, offer favourable conditions for the reproduction of C neoformans. Both Cryptococcus species are associated with decaying vegetation.

Disease signs: Cryptococcosis caused by C neoformans or C gattii is indistinguishable clinically. The disease can present in nasal, central nervous system (which can derive from the nasal form or occur independently), cutaneous and systemic forms.

Diagnosis: An easy and reliable test for cryptococcosis diagnosis is antigen detection in body fluids. Only isolation and polymerase chain reaction allow identification of the species genotype.

Disease management: Amphotericin B, ketoconazole, fluconazole and itraconazole have all been used to treat cats. Surgical excision of any nodules in the skin, nasal or oral mucosa assists recovery. Continued treatment is recommended until the antigen test is negative.

Prevention: Efficient preventive measures have not been demonstrated. Vaccines are not available.

Figure 1

Nasal cryptococcosis: chronic monolateral nasal discharge and mild nasal deformity. Courtesy of Maria Grazia Pennisi

Figure 2

Cryptococcal disease: severe nasofacial swelling and deformity. Courtesy of Maria Grazia Pennisi

Figure 3

Cryptococcal disease: ulcerated skin nodules on the face. Courtesy of Maria Grazia Pennisi

Figure 4

Cryptococcal disease: keratouveitis and cryptococcoma in the anterior chamber. Courtesy of Maria Grazia Pennisi

Figure 5

Thoracic radiography, ventrodorsal view: diffuse, multiple, poorly defined nodules with blurred margins in the lungs of a cat with systemic cryptococcosis. Courtesy of Maria Grazia Pennisi

Figure 6

Diff Quick stained smear of nasal exudate from a cat with C neoformans infection. Note the prominent capsule (clear halo) and narrow-necked budding (arrow). Courtesy of Richard Malik, University of Sydney Veterinary School, Australia

Figure 7

Diff Quick stained smear of fine needle aspirate of a cryptococcal lesion. Note the enormous capsule surrounding the yeast cells. Courtesy of Mark Krockenberger

Figure 8

Early invasion of C gattii into the respiratory epithelium of a koala. Note the eosinophilic body surrounded by a clear halo. Courtesy of Mark Krockenberger

Figure 9

Use of immunohistology to demonstrate C gattii in histological sections. It is possible to conclusively identify Cryptococcus species in paraffin-embedded formalin-fixed tissue sections using monoclonal antibodies directed against different capsular epitopes. These show up as brown precipitates, highlighting both the yeast cell body and its capsule. Note also the narrow neck budding. Courtesy of Mark Krockenberger