56 (167)

capsule (1-30 pm). This capsule is responsible for the virulence of this fungus and explains its resistance to desiccation. It is not a true yeast as a phase of sexual reproduction (mycelial form) can be demonstrated under laboratory conditions⁹. Cryptococcosis in man and animals is caused by two varieties of Crypłococcus neoformans: Cryptococcus neoformans var. neoformans (3 serotypes: A, D and AD) and Cryptococcus neoformans var. gattii (2 serotypes: B and C). In man, in Europę, North America and Japan, most strains correspond to Cryptococcus neoformans neoformans whereas in Central and South America, Africa and Australia, Cryptococcus neoformans gattii is the most prevalent strain ^l0. There is little information regarding the relative importance of the two varieties in the dog and cat. One recent Australian study has shown that out of 27 cats, Cryptococcus neoformans neoformans was isolated in 21 animals and Cryptococcus neoformans gattii in the other six Pigeon droppings, and soil that has been contaminated by them, contain a reservoir of Cryptococcus neoformans. This fungus lives in birds’ intestines where it utilises creatinine as a source of nitrogen. Cryptococcus neoformans gattii has only been isolated from soil around Eucalyptus trees.

The majority of cases are caused by the inhalation of cryptococci which are then spread via the blood to the nasal cavity, lungs and other organs, especially the nervous system, lymph nodes, eyes, kidneys and skin. Morę rarely, animals such as man are infected via the skin The development and spread of the infection are strongly dependent on the host’s immune system. Cell-mediated immunity is most important in preventing and eliminating the infection. Most people affected are immunosuppressed (e.g. by AIDS, corticosteroid treatment or other immunosuppressive treatments). In the cat, no epidemiological studies have been carried out although immunosuppressive illnesses such as FIV and FeLV infections, and lymphoma, may be predisposing factors. However, an underlying illness is rarely demonstrated in cats with cryptococcosis.

No age, sex or breed predisposition has been demonstrated although in some studies, Siamese and Abyssinian cats are well-represented¹³.

Clinical features

Cryptococcosis is the most common systemie mycosis in the cat.

Systemie signs (e.g. respiratory, neurological and ocular) are common and varied. Sneezing, sniffing and a haemorrhagic, seropurulent discharge are often seen. The lungs are rarely affected. Neurological signs, including depression, passing out, tuming round in circles, pressing against the wali, ataxia and paresis, vary according to which part of the central nervous system is affected. The most common ocular signs are anterior uveitis, blindness due to detached retina, chorioretinitis and panophthalmia.

Dermatological signs involve single or multiple nodules, uleers and draining tracts, affecting mainly the face (the nose is affected in about 70-80% of cases^l4) (Figs 5 : 9-13), pinnae and footpads. Peripheral lymphadenopathy is often seen (Fig. 5 :14).

Diagnosis

Diagnosis is based on the history and suggestive clinical signs (e.g. multicentric nodular lesions affecting mainly the face...), cytology, histopathology, Identification of circulating antigens and fungal culture.

Cytological examination of fine needle aspirates from lesions reveals pyogranulomatous or granulomatous inflammation with numerous pleomorphic yeast-like organisms (Fig. 5 : 15). Fungal elements have the appearance of spheres surrounded by a bright refractile halo which stains particularly well with Indian ink (Fig. 5 : 16). Narrow-based budding is common.

Histopathological examination of skin biopsies reveals either a pyogranulomatous or granulomatous reaction, rich in fungal elements (Fig. 5 : 17) or sometimes, in immunocompromised individuals, the presence of yeasts with no real granulomatous reaction. Special stains (Gomori, mucicarmine red) are useful for identifying these yeasts (Figs 5 :18,19).

A latex agglutination test can be used to detect capsular antigens. It is a very sensitive (morę than 90%) diagnostic procedurę that is ąuick and easy to use^l5. Currently available tests detect all serotypes and can be performed on serum, urine or cerebrospinal fluid (CSF). In the cat, antigenic titres correlate with the