Buruli ulcer

Overview

The Buruli ulcer (also known as the Bairnsdale ulcer) is an infectious disease caused by Mycobacterium ulcerans. The genus also includes the causative agents of tuberculosis and leprosy; Mycobacterium tuberculosis and Mycobacterium leprae, respectively. The early stage of infection is characterised by a painless nodule, with non-pyogenic, necrotising lesions developing in the skin, and occasionally in adjacent bone, as the disease progresses . M. ulcerans secretes a lipid toxin, mycolactone, which functions as an immune suppressant, necrotising agent and activator of cellular apoptosis in mammalian tissues

Symptoms

The infection in most instances presents as a subcutaneous nodule, which is characteristically painless. In southern Australia the presentation is more often as a papule (or pimple), which is in the skin (dermis) rather than subcutaneous. The infection is mostly on the limbs, most often on exposed areas but not on the hands or feet. In children all areas may be involved, including the face or abdomen. A more severe form of infection produces diffuse swelling of a limb, which, unlike the papule or nodule, can be painful and accompanied by fever. Infection may frequently follow physical trauma, often minor trauma such as a small scratch.

Causes

• While the mode of transmission remains unclear, a role has been suggested for fish, aquatic snails, and aquatic plants.
• Schistosomiasis has not been found to increase susceptibility to M ulcerans infection.
• The BCG vaccine has not been shown to protect against the onset of disease, although it has been shown to shorten its duration.

Prevention

Research for a vaccine to treat Buruli ulcer is continuing, although the current Bacille Calmette-Guérin (BCG) vaccine appears to offer some short-term protection. A safe and effective vaccine may be the most effective way to combat Buruli ulcer in the long term.

Diagnosis

The diagnosis of Buruli ulcer is usually based on the characteristic appearance of the ulcer in an endemic area. If there is any doubt about the diagnosis, then PCR using the IS2404 target is helpful, but this is not specific for M. ulcerans. The Ziehl-Neelsen stain is only 40–80% sensitive, and culture is 20–60% sensitive.

Prognosis

If patients seek treatment at the early stage, antibiotics can prove to be successful. Delayed treatment may cause irreversible deformity, long-term functional disability such as restriction of joint movement, extensive skin lesions and sometimes life-threatening secondary infections.

Treatment

Treatment is by surgical excision (removal) of the lesion, which may be only a minor operation and very successful if undertaken early. Advanced disease may require prolonged treatment with extensive skin grafting. Surgical practice can be dangerous and scarcely available in affected third world countries. Antibiotics currently play little part in the treatment of Buruli ulcer.

The WHO currently recommend rifampicin and streptomycin for eight weeks in the hope of reducing the need for surgery. The combination of rifampicin and clarithromycin has been used for many years in Australia. Rifampicin must never be used alone because the bacterium quickly becomes resistant.

Resources

Early diagnosis and treatment are vital.