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A Practical Guide to Feline Dermatology

Nocardiosis

Aetiopathogenesis

Nocardiosis is a very rare skin infection caused by filamentous bacteria of the genus Nocardia. Colonies form grains within pyogranulomatous reactions. These bacteria are aerobic, gram-positive and partially acid-fast soil saprophytes. Various species may be isolated including Nocardia asteroides, and morę rarely Nocardia caviae and Nocardia brasiliensis ^l3.

Pathogenesis is poorly understood. Infection may occur via a scratch or bite. In immunosuppressed cats, infection may arise by inhalation and spread to other organs.

Clinical features

Dermatological signs occur mainly on the face, distal limbs (Fig. 6 : 13) or abdomen. They are characterised by ulcerated lesions, draining tracts and pus containing white and yellowish grains¹³

Systemie signs are common and relate to underlying illness: pyrexia, regional lymphadenopathy, dyspnoea (if pyothorax), etc...¹³.

Diagnosis

The diagnosis is based on lesion distribution, suggestive skin biopsies, and identification of the bacteria by bacterial culture.

Cytological examination of grains reveals filamentous bacteria arranged in stars.

Histopathological examination of deep skin biopsies reveals a nodular or diffuse dermatitis and/or a pyogranulomatous panniculitis with or without grains. Colonies of Nocardia spp. appear partially acid-fast when stained with modified Fite-Faraco³.

Bacterial culture is performed on skin biopsies taken aseptically and inoculated onto aerobic media. Antibiotic sensitivity testing should be conducted.

Prognosis - Treatment

The prognosis is guarded, depending on the presence of an underlying illness.

Treatment is difficult. Broad surgical excision of the lesion and debridement, involving curettage and antiseptic flushing, are possible in some cases. Therapy based on antibiotic sensitivity testing is essential. Orał trimethoprim-sulphamethoxazole (30 mg/kg BID) is given until lesions have resolved and for one month after. Other antibiotics such as penicillin G (100,000 IU/kg SID), given by intramuscular injection over 10 days, may be used (Table 6:1)

Actinomycosis

Aetiopathogenesis

Actinomycosis is a very rare skin infection caused by filamentous bacteria of the genus Actinomyces. Colonies form grains within granulomatous reactions. These bacteria form part of the resident bacterial flora in the buccal cavity and intestine. They are gram-positive, anaerobic and non-acid-fast.

Pathogenesis is poorly understood. Infection occurs mainly via wound contamination (e.g. bites and scratches). In immunosuppressed cats, infection may arise by inhalation and spread to other organs. Apparently, the condition is not dependent on immunosuppression of the host.

Clinical features

Dermatological signs occur mainly on the face, neck and trunk and are characterised by variably circumscribed abscesses, draining tracts (Fig. 6:14) and pus, containing yellow sulphur grains.

Systemie signs generally reflect the degree of systemie involvement.

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