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Sporotrichosis

Sporotrichosis is a fungal infection of the skin caused by the fungus Sporothrix schenckii, which is found on decaying vegetation, rosebushes, twigs, hay, sphagnum moss and mulch-rich soil.

Causes

The most common route of infection is via the skin through small cuts, scratches or punctures from thorns, barbs, pine needles or wires. Sporotrichosis does not appear to be transmitted from person to person but there are reported cases of transmission from infected cats to humans. In very rare cases, spore-laden dust can be inhaled or ingested and in people with a weakened immune system cause disseminated (widespread) sporotrichosis.

People at risk of contracting sporotrichosis include farmers, nursery workers, landscapers and gardeners. Adult males are, by their occupation, most exposed to the risk of infection.

Clinical features

Depending on the severity of infection and the overall well-being of the individual, sporotrichosis can present in several ways. Skin disease is the most common.

Presentation	Features
Skin disease	Patients are typically well without fever Lesion develops at the site of a scratch Nodules appear under the skin along the lymphatic channels
Lung disease	Patients usually have severe underlying chronic lung disease and present with pneumonia They may or may not have skin lesions
Bones & joint disease	Patients typically present with a subacute or chronic inflammatory arthritis involving one or more joints They may or may not have skin lesions
Disseminated disease	Patients present with skin lesions but may have other organ involvement including the eye, prostate, oral mucosa, larynx and brain Spreading usually occurs only in people with a weakened immune system, e.g. HIV or AIDS patient

Cutaneous and lymphocutaneous sporotrichosis

This is the most common presentation of sporotrichosis. It occurs following the implantation of spores in a wound. Lesions usually appear on exposed skin and often the hand or forearm is affected, as these areas are a common site of injury. Features of cutaneous sporotrichosis include:

The first lesion can take up to 20-90 days to appear after initial cutaneous inoculation. Usually the first visible nodule occurs within 20 days.
The first sign is a firm bump (nodule) on the skin that can range in colour from pink to nearly purple. It is usually painless or only mildly tender.
The nodule gradually grows bigger, reddens, becomes pustular, and ulcerates. The open sore (ulcer) may drain clear fluid.
If left untreated, the nodule and the ulcer become chronic and remain unchanged for years.
In about 60% of cases, the infection spreads along the lymph nodes and a chain of lymphatic nodules develop in a line up the infected arm (or leg) leading away from the initial ulcer. These also develop into ulcers and can last for years if left untreated.

Diagnosis

Microscopy and culture of infected tissue is performed to identify the presence of Sporothrix schencki. Other infections can mimic the lesions of sporotrichosis so it is important to perform tests to confirm diagnosis. Other possible infections include bacteria related to tuberculosis or leprosy, cowpox, herpes simplex, other fungi and bacteria, and non-infectious diseases such as lupus erythematosus.

Treatment

Treatment of sporotrichosis depends on the site infected.

Site of infection	Treatment
Skin	Traditionally treated with saturated potassium iodide solution given orally 3 times per day for 3-6 months until all lesions have gone. Itraconazole orally for up to 6 months.
Bones and joints	Difficult to treat and rarely respond to potassium iodide. Itraconazole orally for months or even up to a year. Amphotericin IV if oral therapy ineffective. Surgery to remove infected bone.
Lungs	Potassium iodide, itraconazole and amphotericin used with varying degrees of success. Infected areas of lung may need to be surgically removed.
Disseminated (e.g. brain infection)	Itraconazole may be tried Amphotericin plus 5-fluorocytosine is generally recommended.

Treatment can be prolonged but should continue until all lesions have resolved. This may take months or years, and scars may remain at the original site of infection. However, most people can expect a full recovery. Systemic or disseminated sporotrichosis is usually more difficult to treat and in some cases life-threatening for people with weakened immune systems.

Patients should be advised of measures to take to prevent sporotrichosis. These include wearing gloves, boots and clothing that covers the arms and legs when handling rose bushes, hay bales, pine seedlings or other materials that may scratch or break the skin surface. It is also advisable to avoid skin contact with sphagnum moss.

Related information

References:

Book: Textbook of Dermatology. Ed Rook A, Wilkinson DS, Ebling FJB, Champion RH, Burton JL. Fourth edition. Blackwell Scientific Publications.

On DermNet NZ:

Other websites:

Sporotrichosis – emedicine dermatology, the online textbook

Books about skin diseases:

See the DermNet NZ bookstore

Author: Vanessa Ngan, staff writer