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A Practical Guide to Feline Dermatology

Sporotrichosis

Sporotrichosis is a deep mycosis, highly contagious to man, caused by a dimorphic fungus, Sporothrix schenckii⁵. This infection should be suspected in cats with a non-healing wound or abscess following the use of appropriate antibiotics. Sporotrichosis is a serious zoonosis and individuals in direct contact with soil and plants should be considered at risk⁶.

Infection in the cat usually results from wound contamination or penetration of a foreign body. Morę rarely, inhalation of spores can cause systemie illness. Man usually becomes infected directly following a bite or scratch but infection can also arise by direct contact with infected tissues or fluids of affected cats.

Signs are identical to those described in the cat⁷. The ineubation period is variable (3 weeks to 3 months). The cutaneolymphatic form is the most common (seen in 80% of cases), characterised by a solitary nodule at the site of infection. The nodule, which eventually uleerates, is typically seen on the back of the hand (Fig. 25 : 9), a finger, a toe, or the face. Other nodules may appear along lymphatic vessels. The strictly cutaneous form is identical to the feline condition. The rare systemie form is probably caused by spread of infective Sporothrix schenckii spores via the blood. Usually, sporotrichosis can be treated successfully in immunocompetent people but it can be fatal in the immunosuppressed.

Diagnosis is based on cytology, histopathology and fungal culture⁸. In man, diagnosing the condition on histopathology is difficult due to possible confusion with Cryptococcus neoformans and Histoplasma capsulatum.

In the cat, in addition to systemie antifungal treatment, hygienic measures must be carried out. Hands and arms must be thoroughly cleaned with antifungal agents like chlorhexidine and povidone-iodine. Wearing protective gloves is also recommended. Owners must be informed of the considerable zoonotic risk associated with this illness and euthanasia should be discussed for carrier cats because treatment is long and the risk of transmission is high⁹.

Blastomycosis

Blastomycosis is a systemie mycosis, caused by the fungus, Blastomyces dermatidis, reported mainly in North America, but also in Africa and central America, with well-defined endemic foci. Blastomycosis is a systemie illness seen in the dog and man, and rarely in the cat. To datę, no case has been reported in Europę in the cat. Humań infection can occur via wound contamination (bites from infected animals; knives or needles contaminated by autopsy or aspirate). In addition to characteristic pulmonary lesions following inhalation of spores from the soil, skin lesions can occur. These may take the form of papules and abscesses or sometimes proliferative, crusting nodules with a raised border. Diagnosis is based on fungal culture carried out by specialist laboratories⁵.

Histoplasmosis

Histoplasmosis is a systemie mycosis, caused by a dimorphic fungus, Histoplasma capsulatum. There are two varieties of this fungus: var. capsulatum (American histoplasmosis) and var. duboisii (African histoplasmosis). The disease is endemic in the Southern United States and also in many tropical countries. It is reported sporadically in other parts of the world, notably Europę¹⁰. Histoplasmosis is a systemie disease seen in the dog, cat and man. The disease is contracted by inhalation of spores from contaminated soil, contact with contaminated bird or bat faeces or by contact with wounds contaminated by the fungus. In man, histoplasmosis is a marker for AIDS. American histoplasmosis is characterised by mucocutaneous lesions such as gingivitis and well-circumscribed uleeration of the palate and tongue. African histoplasmosis is characterised by cutaneous lesions: semicircular, lenticular papules, sometimes with a depressed centre, or nodules, indolent uleers and fistulae ⁷. Diagnosis is based on fungal culture carried out by specialist laboratories and histopathology of skin lesions⁵.

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