54 (167)

A Practical Guide to Feline Dermatology

Clinical features

The disease can present in three clinical forms: cutaneous, cutaneolymphatic and systemie \ It is likely that the clinical form reflects the cat’s immune response, the localised form relating to an immune system that is only slightly disordered. However, most affected animals present with intemal lesions on necropsy. Dermatological signs are characterised by ulcerated nodules on the head (Figs 5 :5,6), taił base and limbs (Fig. 5 : 7). Extensive necrosis occurs which may also affect muscle and even underlying bonę. With grooming, cats may spread fungal organisms over the entire skin surface. The disease frequently becomes generalised, via the lymphatics, and causes pulmonary, renal, digestive and central nervous system lesions. Fever is often seen.

Diagnosis

Diagnosis is based on the history and, mainly dermatological, clinical signs (ulcerated neerotie nodules on the face, taił and limbs, following a bite or scratch, and non-responsive to appropriate antibiotic treatment). Cytological and histopathological examination of deep samples and fungal culture are the most useful diagnostic tests.

Cytological examination of exudate and histopathological examination of deep samples usually reveals very large numbers of fungal elements. Sporothrix schenckii is a very pleomorphic yeast. Its most typical form is cigar-shaped, 2-4 pm long and either intracellular or extracellular (Fig. 5:8). On histopathological examination, the refractile celi wali of Sporothrbc schenckii, and the fragmented cytoplasm may give the impression of a capsule. Special stains (PAS, Gomori) will differentiate Sporothrix schenckii and Cryptococcus neoformans. In the cat, the inflammatory infiltrate is granulomatous with epithelioid macrophages and lymphocytes. Immunofluorescent techniques are sometimes useful when demonstrating and / or growing the fungus is difficult.

Fungal culture of deep tissue samples can be used to isolate and identify the fungus. Sporothrix schenckii grows as a yeast on blood agar at 37°C and in mycelial form on Sabouraud’s agar at 25°C. Microscopic examination of colonies reveals branching, filamentous hyphae, with piriform conidia and rosette-shaped conidiophores.

Treatment

Treatment is based on the use of orał itraconazole (5 mg/kg BID) for at least two months. Orał potassium iodide (20 mg/kg BID), with food, can also be used and must be continued for at least one month beyond clinical resolution. However, iodide derivatives are not always well tolerated in cats and may cause side-effects (e.g. depression, vomiting, anorexia, hypothermia and cardiac insufficiency). Antibiotics are also desirable when there is secondary bacterial infection.

Risks for public health

Feline sporotrichosis is very contagious to man, probably because of the large number of fungal elements present in infected tissues. Man can become infected following a bite or scratch from an affected cat, or even by direct contact with infected tissues or body fluids. Gloves should, therefore, always be wom if sporotrichosis is suspected. The most common form in man is the cutaneolymphatic form. The extracutaneous form, which starts in the lungs, before becoming systemie, is rare but can be seen in immunosuppressed patients⁸.

Cryptococcosis

Aetiopathogenesis

Cryptococcosis is a systemie mycosis caused by an encapsulated saprophytic fungus, Cryptococcus neoformans. Although there are other species, Cryptococcus neoformans is the only one that can grow at 37°C and consequently the only one that is pathogenic. Cryptococcus neoformans is a round yeast-like fungus, 3.5-7 pm in diameter, capable of forming a thick heteropolysaccharide

5.4|