Mulcerans.htm

Mycobacterium ulcerans infection in Australia (Buruli ulcer, Bairnsdale ulcer, Daintree ulcer)

(last updated November 2007)

Contents:

What is Mycobacterium ulcerans infection?

How do you get infected?

Endemic areas (Australia)

What are the symptoms and signs?

Treatment

Pictures (confirmed cases from Australia-warning medical photos.

Notes for Clinicians (on diagnosis)

Useful links

About this website

What is Mycobacterium ulcerans infection? Buruli ulcer, Bairnsdale ulcer and Daintree ulcer are all local names given to the same disease which is caused by a bacterium called Mycobacterium ulcerans. This environmental mycobacterium produces a toxin (mycolactone) that kills fat cells beneath the skin, blocks capillaries and inhibits the local immune response. The disease is generally an ulcerative condition of the skin and subcutaneous fat. The infection occurs in humans, possums, koalas, potoroos and occasional other species. In the popular press and on television the infection is sometimes called the “the flesh-eating bug”. While the toxin produced by Mycobacterium ulcerans does kill tissue (flesh), the process is slow--Mycobacterium ulcerans infection is not a medical emergency.

How do you get infected? The infection is transmitted from the environment. In Victoria (southeastern Australia) there is new evidence that mosquitoes may transmit the infection in certain specific “endemic areas”. Mycobacterium ulcerans does not spread from person to person.

Endemic areas In Australia cases occur each year in east Gippsland (Victoria), far north Queensland, the wet tropics and increasingly in coast towns near Melbourne. The annual number of cases is increasing with at least 66 for Australia in 2006, 61 of whom were from Victoria. In Victoria, clusters of cases have occurred at Phillip Island (1993-5), the Mornington Peninsula (1990-2007), St. Leonard's (1998-2007), Point Lonsdale (2001-2007) and Barwon Heads (2005+). Overseas, the incidence is often much higher, especially in rural West and sub-saharan Africa where there have been tens of thousands of cases in the last 20 years.

The disease is notifiable in Victoria and case numbers can be viewed on the Victorian Department of Human Services daily reports (see link to “Daily Reports” below).

What are the symptoms and signs? The infection usually starts as a small spot attached to the skin that enlarges over days to weeks. Some patients describe a dry scab that won't heal which then breaks down into an ulcer. Sometimes an insect bite is remembered but this is not universal. In Africa, a nodule (mobile lump) beneath the skin may be the first sign. In Australia lesions are typically solitary and mostly occur on the lower leg or arm. However, they can be anywhere. They are usually (but not always) painless and fever or other symptoms of infection are usually absent. Eventually the spot breaks down at the centre and a slowly enlarging undermined ulcer appears. A recent case had a plaque-like patch on her ankle with no ulcer. Very occasional patients present with an acute swelling of the whole limb or whole abdominal wall, without an identifiable nodule or ulcer.

Treatment Extensively damaged areas of skin and soft tissue may require surgical resection and grafting. However there is increasing evidence that M. ulcerans infection does respond to combination drug therapy (eg rifampicin + streptomycin or rifampicin + a second oral anti-mycobacterial drug (see links to treatment guidelines below). In Australia conservative surgery and combination oral drug therapy for 3 months is widely practised. Humans develop natural immunity after several months but skin damage may be extensive by this time. Early intervention leads to minimal scarring.

Pictures (confirmed cases from Australia)

Ear: 18 month child, coastal Victoria, Australia [RCH, Melbourne]

Leg, 11 year old boy, coastal Victoria, Australia [Photo: Dr. Paul Johnson, Austin Hospital, Melbourne].

Elbow, 75 year old man, surgical photo showing resection of ulcer
[Photo A/Prof. John Hayman and Mr. John Buntine, Melbourne].

Leg, adult female, early diagnosis. [Photo: Courtesy Dr. Paul Flood, Phillip Island].

Elbow, 9 year old girl, late diagnosis. [Photo: Dr. Paul Johnson, RCH, Melbourne]

Shoulder, 5 year old girl, Mornington, Victoria; 2006; late diagnosis. Photo courtesy of her parents.

Ankle - 23 yo woman, plaque-like lesion (no ulcer apparent when diagnosed by biopsy)

Microscopy: Acid fast bacilli (M. ulcerans ) in a smear taken from a swab of an ulcer. The bacteria can be clearly seen as red clumps on a blue background. Oil immersion microscopy.

Notes on diagnosis for clinicians

Think of the diagnosis--has the patient been to an at-risk area?

• Obtain a smear for acid fast bacilli (AFBs) using a swab that is run around the undermined edge of an ulcer (if present).

• Ask for routine microscopy and culture and an AFB stain and culture for M. ulcerans.

• If the smear is positive, the diagnosis is reasonably likely.

• If the smear is negative, the diagnosis has not been excluded.

• A diagnostic PCR is now available which can confirm the diagnosis in a few days if AFBs were visible on the smear. You can do the PCR straight from an ulcer swab.

• If there is still doubt, or if there is a suspicious necrotic skin lesion that has not ulcerated, perform an incisional or excisional biopsy.

• Histological sections show extensive necrosis, and there are often large numbers of AFBs. PCR and culture of the biopsy specimens usually confirms the diagnosis. Granulomatous inflammation is sometimes seen in lesions that have been present for some time, and may herald the onset of healing.

• Culture is the gold standard, which takes 8-12 weeks, but you will need to treat the patient before culture results are available. PCR is generally more sensitive than culture.

• NOTE: Negative swabs, and even negative incisional biopsies do not absolutely exclude the diagnosis because the organisms may not be spread evenly through the lesion. If in doubt, repeat biopsies.

Links to guidelines, articles and useful sites

World Health Organization