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Guide to Feline Dermatology

L. Ferrer - A. Fondati

Deep mycoses

Deep mycoses are caused by the growth and proliferation of saprophytic fungi that normally live in the soil, vegetation or decomposing organie matter, within subcutaneous connective tissue and intemal organs. Most of them are considered opportunistic pathogens. In man, they cause diseases in neutropenic or immunodeficient individuals The link between deep fungal infections and the immune system still requires clarification in veterinary medicine, although the majority of cases probably arise following a reduction in the cell-mediated immune response.

Fungi entering the individual subcutaneously, following a break in the epidermis, are responsible for subcutaneous mycoses, whereas those that are inhaled cause systemie mycoses. Systemie mycoses occur initially in the lungs before disseminating via the lymphatics and blood, to other intemal organs and the skin. Clinically, subcutaneous mycoses are characterised by the presence of one or multiple nodules, located mainly on the abdomen, and an absence of systemie signs. Systemie mycoses present similarly on the face and also on the distal limbs and nasal mucosae. The cat is affected systemically and lymphadenopathy, respiratory, nervous, ocular and bony signs may be present.

It is important to be aware of deep mycoses as they enter into the differential diagnosis of many feline dermatological conditions. Prognosis is always guarded. Although deep mycoses are rarely contagious to man, some of them, such as sporotrichosis, histoplasmosis, blastomycosis and coccidioidomycosis are highly zoonotic.

Subcutaneous mycoses

Aetiopathogenesis

Subcutaneous mycoses are rare opportunistic infections caused by the multiplication of ubiąuitous saprophytic soil fungi. They are characterised by dermal or subcutaneous pyogranulomatous lesions following traumatic inoculation of fungi into the skin. Fungi responsible for subcutaneous mycoses belong to various taxonomic groups. The classification of these mycoses is not elear, but one system has been put forward by Foil².

-    Mucormycosis (zygomycosis) caused by fungi of the genera Rhizomucor and Mortierella among others,

-    Hyalohyphomycosis caused by fungi of the genera Fusarium and Paecilomyces among others,

-    Phaeohyphomycosis caused by fungi of the genera Alternaria, Bipoloris, Cładosporium, Exophiala, Moniliella, Phialophora, Scolecobasidium and Stemphyllium among others,

-    Dark-grain, eumycotic mycetoma caused by fungi of the genera Cwyularia and Madurella among others,

-    Pythiosis caused by Pythium insidiosum.

Clinical features

Mucormycosis and hyalohyphomycosis are rarely described in the cat. They involve systemie signs morę than subcutaneous lesions.

Phaeohyphomycosis is morę commonly seen in the cat than the dog. It manifests clinically as nodules (Figs 5 : 1,2), usually solitary, on the face and distal limbs, with variable uleeration and draining traets. The brain, nose and comea may also be affected.

i 5.1