Buruli ulcer

Background

Buruli ulcer is a necrotising disease (causing tissue death) of the skin and underlying tissue, caused by bacteria called Mycobacterium ulcerans. These bacteria are atypical mycobacteria, and come from the same family of organisms that cause leprosy and tuberculosis.

Buruli ulcer is found in more than 30 tropical and subtropical countries. The majority of cases occur in central and western Africa. Cases have also been reported from Australia, South East Asia, and Central and South America. Over the last 2 decades the incidence of Buruli ulcer has increased, despite significant underreporting of cases. In 1999 there were 6000 new cases in Ghana; in Australia, there were 25 cases in 2004, 47 in 2005 and 72 in 2006.

Buruli ulcer predominantly affects poor rural communities living near swampy terrain. Although the exact mode of transmission is unknown, M ulcerans most likely causes infection through contamination of a traumatic wound. People of any age can be affected, but most cases are among children aged less than 15 years.

Clinical features

The incubation period ranges from a few weeks to months. Buruli ulcer begins as a firm, painless nodule (swelling) in the skin, which is around 1 to 2 cm in diameter. M ulcerans produces a toxin, called mycolactone, which is directly toxic to cells and also dampens the immune system. Therefore this toxin causes extensive tissue destruction, without any systemic symptoms (such as fever, malaise, or enlarged lymph nodes).

Over the following weeks, the nodule breaks down to form a painless necrotic ulcer with undermined edges (tissue destruction underlying intact skin). The necrosis may extend several centimetres beyond the edges of the ulcer, making the lesion appear smaller than its actual size. The ulcer can extend down into deeper tissues destroying nerves, blood vessels, muscles, and occasionally bone. The limbs, particularly the lower limbs, are most commonly involved.

Complications

Tissue destruction can be extensive (involving up to 15% of the patient’s skin surface) and secondary infection may occur. Other complications include osteomyelitis (infection of the bone) and metastatic lesions (spread of the lesions to distant sites). Extensive lesions heal with scarring, which may cause irreversible deformity, secondary lymphoedema (swelling due to fluid retention), and restriction of joint movement. Few people die from Buruli ulcer, but it often causes long-term disability, disfigurement, and a significant socioeconomic burden.

Diagnosis

• In endemic areas Buruli ulcer is often diagnosed and treated based on clinical findings.
• A direct smear taken from the necrotic base of the ulcer can be stained with Ziehl-Neelsen stain and may reveal clumps of acid-fast bacilli (mycobacteria) under a microscope.
• M ulcerans can also be cultured from swabs taken from the ulcer or fresh tissue biopsies, but this process takes 6 to 8 weeks or more.
• Polymerase chain reaction (PCR) testing on swabs of ulcers or tissue biopsies.
• Biopsy of the lesion can reveal characteristic microscopic changes and clumps of acid-fast bacilli.

Treatment

1. A combination of rifampicin and streptomycin/amikacin for eight weeks as a first-line treatment for all forms of the active disease. Antibiotics can promote healing of smaller lesions and decrease disease recurrence. The best outcomes occur with early treatment (i.e. lesions <5 cm).
2. Surgery to remove necrotic tissue, cover skin defects, and correct deformities.
3. Interventions to minimise or prevent disabilities.

BCG vaccination appears to offer some short-term protection (less than one year) from the disease.