Be Alert! Increased incidence of Buruli ulcer in Victoria.

What is the issue?

Buruli ulcer is a skin infection caused by the bacterium Mycobacterium ulcerans (M. ulcerans) presenting as a slowly developing painless nodule or papule which can initially be mistaken for an insect bite. Over time the lesion can progress to develop into a destructive skin ulcer which is known as Buruli ulcer or Bairnsdale ulcer.

Buruli ulcer was first diagnosed in the Bairnsdale area in the 1930s. Since then a growing number of cases have been reported in the Bellarine Peninsula and since 2012, the Mornington Peninsula. Although the areas with risk are slowly changing, there are three recognised levels of risk within the overall endemic parts of Victoria.

The highest risk is associated with the active transmission areas of Rye, Sorrento, Blairgowrie and Tootgarook on the Mornington Peninsula. There is a moderate risk associated with areas in the Bellarine Peninsula (Ocean Grove, Barwon Heads, Point Lonsdale, Queenscliff), Frankston and Seaford areas. There is a low but material risk associated with the rest of the Bellarine and Mornington Peninsula, the South Eastern Bayside suburbs and East Gippsland. Together, all these areas are considered the endemic parts of Victoria for Buruli ulcer transmission.

In 2017 there were 275 cases of Buruli ulcer reported in Victoria, compared with 182 cases in 2016 and 107 cases in 2015. In 2018, there have been 31 cases reported to date, compared to 38 cases reported to the same time last year.

When recognised early, diagnostic testing is straightforward and prompt treatment can significantly reduce skin loss and tissue damage.

Who is at risk?

Everyone is susceptible to infection. While it can occur at any age, people aged 60 years and over have a higher rate of notification of Buruli ulcer in Victoria. Individuals who live in or visit endemic areas are considered at greatest risk.

Symptoms and transmission

The incubation period has been estimated to vary from four weeks to nine months, with a median of four to five months. There is a peak in diagnoses in Victoria between June and November each year; however cases are diagnosed year round.

The first sign of Buruli ulcer is usually a painless, non-tender nodule or papule. It is often mistaken for an insect or spider bite and is sometimes itchy. The lesion may occur anywhere on the body but it is most common on exposed areas of the limbs. In one or two months the lesion may ulcerate, forming a characteristic ulcer with undermined edges. The bacterium produces a unique toxin known as mycolactone that inhibits the immune response whilst continuing to damage tissue. If left untreated, extensive ulceration can occur, requiring surgical management.

Occasionally the disease may present as a firm, painless elevated plaque or a large area including a whole limb may be indurated by oedema without an ulcer. Oedematous lesions are a less common but represent a more severe form of the disease and are more likely to be accompanied by fever and cellulitis. In patients with cellulitis that does not respond as expected to usual antibiotics, the diagnosis of Buruli ulcer should be considered, especially in those with reported exposure to an endemic area and cellulitis that has affected the ankle, wrist or elbow regions.

Transmission pathways of M. ulcerans are not well understood. The bacteria may enter through broken skin, and both mosquitoes and some water-dwelling insects have been implicated in the transmission pathway. Most cases report some form of skin trauma, including insect bites, prior to the development of the lesion. The disease is not transmissible from person to person.

Recommendations

Preventive measures

Simple precautionary measures such as wearing appropriate protective clothing when gardening or undertaking recreational activities in endemic areas, especially those with active transmission, 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. Although not confirmed, it is possible that M. ulcerans may be transmitted by mosquito bites, therefore the use of insect repellent when outdoors during warmer months is recommended.

Diagnosis

Two dry swabs (or pre-moistened with sterile saline) from beneath the undermined edges of the lesion or one swab and one biopsy should be sent for staining for acid-fast bacilli (AFBs), polymerase chain reaction (PCR) and culture. For accurate test results, it is recommended to always send two separate swabs or a swab and a biopsy, so that one dedicated swab can be sent directly to the Victorian Infectious Diseases Reference Laboratory (VIDRL) for PCR testing. It is essential that there is visible clinical material on the swab. Please state on the request form that Buruli ulcer or M. ulcerans is suspected so that one swab can be reserved for VIDRL and not split for other laboratory testing such as culture.

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 only performed at VIDRL and can confirm the diagnosis in a few days. Culture usually takes eight to 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 mycobacterial culture.

Under the Public Health and Wellbeing Regulations 2009, Buruli ulcer is a Group B disease and must be notified in writing by medical practitioners and persons in charge of laboratories within five days of diagnosis.

Management

Referral for treatment to doctors experienced in the management of this condition is recommended. The current mainstay of treatment is rifampicin-containing combination oral antibiotic therapy. Surgery may be used in combination with antibiotic therapy where indicated.