Mycobacterium ulcerans

Victorian statutory requirement

Mycobacterium ulcerans infection (Group B disease) must be notified in writing within five days of diagnosis.

School exclusion is not required.

Infectious agent

Mycobacterium ulcerans is a member of the mycobacterium family. Tuberculosis, leprosy and many other environmental mycobacteria belong to this family. Mycobacterium ulcerans causes skin ulcers, variously known as the Bairnsdale, Bairnsdale, Buruli, or Daintree ulcer.

Identification

Clinical features
The first sign of M. ulcerans is usually a painless, non-tender nodule or papule. It is often thought to be an insect bite. The lesion may occur anywhere on the body but it is most common on exposed areas of the limbs. Some patients complain that the lesion is itchy. In one or two months the nodule may become fluctuant and ulcerate, forming a characteristic ulcer with undermined edges. Ordinarily there is no regional lymphadenopathy, fever or systemic manifestations associated with the disease. If left untreated extensive ulceration can occur.

Occasionally the disease may present as a firm, painless elevated plaque with irregular edges. Or an entire limb or area may be indurated by oedema without an ulcer being present. The oedematous form may be associated with fever.

Method of diagnosis
Swabs from beneath the undermined edges of the lesion or a biopsy should be sent for staining for acid-fast bacilli (AFBs). Two other swabs should be taken; a dry swab for a polymerase chain reaction (PCR test) and another for culture should be placed in transport medium. Bacterial culture or a specific PCR should be performed to confirm the diagnosis. It should be stated on the request form that M. ulcerans is suspected.

A positive smear for AFBs makes the diagnosis likely. Culture or PCR is required for confirmation. A negative smear does not exclude the diagnosis.

The PCR test is performed at the Victorian Infectious Diseases Reference Laboratory (VIDRL). This test can give rapid confirmation of the diagnosis within a few days. Culture of the organism usually takes 8–12 weeks.

A biopsy of suspicious lesions which have not ulcerated can be sent for histology. The suspected diagnosis should be mentioned and a request made for AFB staining, specific PCR and bacterial culture. Biopsy specimens usually show extensive necrosis, especially of fat. Granulomatous inflammation is usually present in more chronic lesions. AFBs are frequently seen in large numbers.

Incubation period

This has not been clearly defined but is thought to be quite long, i.e. weeks to a couple of months.

Public health significance & occurrence

Although this is not a common cause of ulcers in Australia, it is important that it be considered in the focal areas in which it occurs as early diagnosis and treatment is advisable to minimise tissue damage.

After tuberculosis and leprosy this is the most common mycobacterial disease. The disease exists or is suspected in 31 countries. The majority of the cases occur in foci in west and central Africa, where large, severe disabling ulcers may result in severe contractures or death from extensive skin loss.

In Australia the disease exists in Far North Queensland around the Mossman area and in parts of coastal Victoria including East Gippsland (where it was first described in Bairnsdale and so named), Cowes on Phillip Island, Mornington Peninsula and most recently Bellarine Peninsula.

Reservoir

The organism appears to be associated with usually swampy or stagnant water. The exact reservoir remains unclear.

Mode of transmission

The exact method of transmission of M. ulcerans infection is unclear. Exposure to contaminated water, soil, or vegetation in areas where the disease is known to occur is thought to be required. The bacteria may enter through a breakage in the skin. Exposure to aerosols of contaminated water has been hypothesised to be a method of acquisition. Recently, some insects that live in water have been shown to contain the bacteria and they may play a role in transmission.

Period of communicability

M. ulcerans infection is not (or is rarely) transmitted from one person to another.

Susceptibility & resistance

Everyone is susceptible to infection.

Control measures

Preventive measures
Early recognition and diagnosis is important to minimise the disabling and disfiguring effects of this disease. Referral for treatment by doctors experienced in the management of this condition is recommended. Simple precautionary measures such as wearing appropriate protective clothing when gardening and undertaking recreational activities in identified risk areas may assist in preventing infection. Cuts and abrasions should be cleaned promptly and exposed skin contaminated by suspect soil or water should be washed following outdoor activities.

BCG vaccination is not used for prophylaxis.

Control of case
Isolation is not required. The ulcers do however contain large numbers of organisms and it is possible that person to person infection could occur through breaks in the skin. Thus, it is recommended that ulcers be kept covered and thorough hand washing be performed following dressing changes. Safe disposal of infected material should also occur.

The current mainstay of treatment is surgery with adequate (but not excessive) clearance of the undermined edges of the ulcer. Primary closure may be possible with small lesions but skin grafting of the area may be required for larger areas. Other forms of treatment that may be used, often as an adjunct to surgery, include:

Heat treatment. Continuous local heating promotes healing but care must be taken to prevent burning. The organism grows at 32°C and heat up to 40°C has been used with some effect.
Antibiotic treatment. A number of antibiotics have been found to be active against the organism in vitro. These include clarithromycin, rifampicin, azithromycin and amikacin. Combinations of these have been used, often to mop up residual organisms after surgery in an attempt to prevent recurrence.

Occasionally small lesions have been reported to heal spontaneously.

Control of contacts
Not applicable.

Control of environment
Not applicable.

Outbreak measures

Clusters of cases are investigated looking for a common source where an intervention may be feasible and advisable, including health or public alerts.

Additional sources of information

World Health Organization

top of page