zygomycosis

The term zygomycosis describes in the broadest sense any infection due to a member of the Zygomycetes. These are primitive, fast growing, terrestrial, largely saprophytic fungi with a cosmopolitan distribution. To date, some 665 species have been described although infections in humans and animals are generally rare. Medically important orders and genera include:

1. Mucorales, causing subcutaneous and systemic zygomycosis (Mucormycosis) - Rhizopus, Mycocladus (Absidia), Rhizomucor, Mucor, Cunninghamella, Saksenaea, Apophysomyces, Cokeromyces and Mortierella.

2. Entomophthorales, causing subcutaneous zygomycosis (Entomophthoromycosis) - Conidiobolus and Basidiobolus.

Clinical manifestations:

Zygomycosis in the debilitated patient is the most acute and fulminate fungal infection known. The disease typically involves the rhino-facial-cranial area, lungs, gastrointestinal tract, skin, or less commonly other organ systems. It is often associated with acidotic diabetes, starvation, severe burns, intravenous drug abuse, and other diseases such as leukemia and lymphoma, immunosuppressive therapy, or the use of cytotoxins and corticosteroids, therapy with desferrioxamine (an iron chelating agent for the treatment of iron overload) and other major trauma. The infecting fungi have a predilection for invading vessels of the arterial system, causing embolization and subsequent necrosis of surrounding tissue. A rapid diagnosis is extremely important if management and therapy are to be successful.

1. Rhinocerebral zygomycosis:

Predisposing factors include uncontrolled diabetes mellitus or acidosis, steroid induced hyperglycemia, especially in patients with leukemia and lymphoma, renal transplant and concomitant treatment with corticosteroids and azathioprine. Infections usually begin in the paranasal sinuses following the inhalation of sporangiospores and may involve the orbit, palate, face, nose or brain.

Rhinocerebral zygomycosis showing involvement of the palate.

2. Pulmonary zygomycosis:

Predisposing conditions include haematological malignancies, lymphoma and leukemia, or severe neutropenia, treatment with cytotoxins and corticosteroids, desferrioxamine therapy; diabetes and organ transplantation. Infections result by inhalation of sporangiospores into the bronchioles and alveoli, leading to pulmonary infraction and necrosis with cavitation.

3. Gastrointestinal zygomycosis:

A rare entity, usually associated with severe malnutrition, particularly in children, and gastrointestinal diseases which disrupt the integrity of the mucosa. Primary infections probable result following the ingestion of fungal elements and usually present as necrotic ulcers.

4. Cutaneous zygomycosis:

Local traumatic implantation of fungal elements through the skin, especially in patients with extensive burns, diabetes or steroid induced hyperglycemia and trauma. Lesions vary considerably in morphology but include plaques, pustules, ulcerations, deep abscesses and ragged necrotic patches.

Ulcerated cutaneous zygomycosis.

Debridement of subcutaneous zygomycosis.

5. Disseminated zygomycosis:

May originate from any of the above, especially in severely debilitated patients with haematological malignancies, burns, diabetes or uraemia.

6. Central Nervous System alone:

Intravenous drug abuse. Traumatic implantation leading to brain abscess.

7. Infections caused by entomophthoraceous fungi:

Zygomycosis due to entomophthoraceous fungi is caused by species of two genera, Basidiobolus and Conidiobolus. Infections are chronic, slowly progressive and generally restricted to the subcutaneous tissue in otherwise healthy individuals. Other characteristics that separate these infections from those caused by mucoraceous fungi are a lack of vascular invasion or infarction and the production of a prolific chronic inflammatory response, often with eosinophils and Splendore-Hoeppli phenomena around the hyphae.

Zygomycosis caused by B. ranarum is a chronic inflammatory or granulomatous disease generally restricted to the subcutaneous tissue of the limbs, chest, back or buttocks, primarily occurring in children and with a predominance in males. Initially, lesions appear as subcutaneous nodules which develop into massive, firm, indurated, painless swellings which are freely movable over the underlying muscle, but are attached to the skin which may become hyperpigmented but not ulcerated.

Zygomycosis caused by B. ranarum.

Zygomycosis caused by Conidiobolus sp. is a chronic inflammatory or granulomatous disease that is typically restricted to the nasal submucosa and characterised by polyps or palpable restricted subcutaneous masses. Clinical variants, including pulmonary and systemic infections have also been described. Human infections occur mainly in adults with a predominance in males (80% of cases). Most cases have been reported from the tropical rain forest areas of central and west and south and central America. Infections usually begin with unilateral involvement of the nasal mucosa. Symptoms include nasal obstruction, drainage and sinus pain. Subcutaneous nodules develop in the nasal and perinasal regions and progressive generalised facial swelling may occur. Infections also occur in horses usually producing extensive nasal polyps and other animals. Conidiobolus coronatus is also a recognised pathogen of termites, other insects and spiders.