Alternariosis

1 - GENERAL

Alternariosis is an opportunistic fungal infection caused by filamentous moulds of the Alternaria genus. It is considered to be a form of phæohyphomycosis, caused by black fungus whose colour comes from the melanic brown pigment in the filaments. Alternaria infection mainly causes dermal cutaneous lesions. Although still rare, the number of cases reported is constantly increasing in certain populations, such as transplant patients.

Alternaria are saprophytes or plant parasites commonly found in nature. The spores are airborne and enter the body through small cuts or scratches, which explains the higher incidence of alternariosis infection in rural areas and the location of the infection on exposed parts of the skin. In very rare cases in which multiple, widespread foci have been observed, dissemination throughout the body via the blood stream has been suggested.

Most of the cases reported have been observed in Europe. Over half of the cases reported in France (40 percent of all cases published) have been diagnosed in the West of the country (Brittany, Pays-de-la-Loire and Central regions). In most cases, the patients were immunocompromised but, in a small number, no predisposing factors were found. Review of the literature [1] indicates that the main predisposing factor is long-term corticosteroid therapy sometimes combined with immunosuppressant or cytotoxic agents, given to treat a variety of disorders including autoimmune disease, kidney and liver transplants, malignant blood disorders, tumours, nephrotic syndromes and asthma. More rarely, local corticosteroid treatment only has been reported. Alternaria infection has also been reported in patients with other underlying conditions, such as Cushing’s disease, diabetes and, more rarely, AIDS. The cutaneous fragility induced by hypercorticism in patients receiving systemic and local corticosteroids or with Cushing’s disease was a cofactor since it facilitates entry of the fungus into the body. Cutaneous alternaria infection presents as one or more lesions located mainly on exposed areas such as the knees, wrists and dorsum of the hands. They are polymorphous in appearance and their shape also varies depending on the stage of the disease. The most common presentation is violaceous, erythematous and crusted nodules. Neither visceral involvement nor a positive blood culture has been reported even in severely immunocompromised patients and the deaths observed have always been related to the underlying disease.

Direct examination of the lesions or biopsy smears is important since this is a rapid means of diagnosing a fungal infection. The diagnosis is confirmed by the pathology results and a mycological examination of a skin biopsy. As this fungus is ubiquitously present in nature, both these examinations must be positive to confirm its pathogenic role. Histologically, Alternaria infection presents as mixed, well-defined granulomas located in the superficial dermis and sometimes extending into the deep dermis and hypodermis. The fungus appears as rounded elements measuring 3 to 15 µm in diameter and/or short, septated filaments whose walls are intensely stained with PAS and Grocott’s. The Alternaria genus is isolated in mycological cultures. Alternaria alternata and Alternaria tenuissima are the most common species implicated. Molecular biology is a useful means of identifying the species, particularly when no conidian-spores form in the culture. There is doubt as to whether purely epidermal cases of alternariosis infection actually exist. Fungi of the Alternaria genus can cause onychomycoses.