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Buruli Ulcer

Overview

Buruli ulcer is a mycobacterium infection which leads to the formation of ulcers on the limbs, particularly over the joints. In severe cases or infections in children, the infection can present anywhere on the body. The causative organism is Mycobacterium ulcerans, a bacterium which causes necrotic disease. M.ulcerans produces a cytotoxin, mycolactone, which destroys tissue and decreases immune system function through inhibition. The immunosuppressive properties of mycolactone prevent the response of pain or pyrexia at the affected area. The disease mainly affects skin and subcutaneous soft tissue but infection of the bone is possible if left untreated. Although not fatal, absence of treatment can eventually lead to permanent scars, irreversible deformity, socioeconomic factors and functional disability.

Buruli ulcer cases have been reported in 33 countries and are primarily seen in West Africa. Cases are also seen in Australia, South East Asia, China, central and South America. Data is available from 15 of these countries, showing 5000 to 6000 cases reported annually. A number of cases have been reported in non-endemic areas of Europe and North America after international travel. Buruli ulcer is a poorly understood infection which has presented since the 1980s.

 

Symptoms

  • Painless swelling just under the skin (nodule)

  • Large painless plaque

  • White cotton wool-like appearance

  • Oedema of the face, legs or arms

  • Nodule/plaque/oedema then progresses into an ulcer after 4 weeks

  • Ulcer has undermining appearance (overhanging margins)

  • Thickening and darkening of uninfected skin surrounding lesion

  • 85% of ulcers present on the limbs (lower limbs twice as likely than the upper)

Causes

The mode of transmission is still unknown but several hypotheses exist. The infection often occurs in close proximity to water bodies including slow-moving rivers, swamps and wetlands. Buruli Ulcer has also been more closely associated with human-linked changes to aquatic environments, particularly disturbances, such as deforestation, agriculture, mining and construction of dams. Recent evidence suggests aquatic insects, adult mosquitos or other biting arthropods may be vectors or reservoirs for M. ulcerans. Physical trauma to the skin introduces M. ulcerans from surface contamination.

 

Risk factors / at risk groups

  • Children under 15 years old

  • Living in poor, rural communities

  • Proximity to aquatic habitats in endemic areas

  • Human risk factors such as wading, swimming, fishing, bathing, farming

  • More common in Africa during rainy season

  • More common near sea water than fresh water in Australia

 

Diagnosis / microbiology tests

Confirmation of Buruli ulcer disease is achieved through positive results on two or more of the following laboratory tests:

1. acid-fast bacilli (AFB) identified on microscopic smear stained by Ziehl-Neelsen technique

2. polymerase chain reaction (PCR)

3. histopathology

4. culture

However, in the poor, rural areas where the infection is endemic, these laboratory tests are not suitable due to limited resources, with the exception of the AFB smear. Diagnosis in rural areas is based on infection history in the area and typically occurs after treatment has begun.

 

Treatment

Treatment varies due to the progression of the disease. It can be treated with antibiotics alone but in the later stages of infection there is a high risk of treatment failure and antibiotic resistance. 80% of infections caught in the early stages can be treated with combination antibiotics. Treatment commonly requires surgery and skin-grafting with a prolonged course of antibiotics.

 

Typical combination treatment plans for a Buruli Ulcer infection:

* oral rifampicin (10mg/kg od) and iv streptomycin (15mg/kg od)

* oral rifampicin (10mg/kg od) and oral clarithromycin (7.5mg/kg bd) (safer option in pregnancy)

* oral rifampicin (10mg/kg od) and oral moxifloxacin (400mg od) (new – treatment not yet proven in randomised trial)

 

Vaccines / preventative measures

No existing vaccine is currently available. Since the cause of the infection is still unknown, there are no preventative measures to take.

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