Scientists and public health officials are searching for clues behind an outbreak of a rare, flesh-eating bacteria spreading in the southeastern Australian state of Victoria. On Monday, The Medical Journal of Australia reported a 51% increase of cases in the region in 2017 (236) compared to last year (156) of Buruli ulcer, an infectious disease that causes disfiguring skin lesions. There have been 30 new cases reported in 2018 so far. People aged 60 and older have a higher rate of case notifications, but people of all ages are susceptible, including young children. According to the researchers, Victoria (which is home to Melbourne) is facing “a worsening epidemic” of Buruli ulcer characterized by growing numbers of cases, greater severity, and spread to new geographic areas.

The authors call for “an urgent scientific response” to tackle the epidemic, and they outline a specific research agenda. Importantly, the mode of transmission remains unknown. Below we examine some of the public health questions surrounding the outbreak of Buruli ulcer which will need to be explored to make progress in preventing future cases of this necrotizing disease.

A Changing Threat

Buruli ulcer is a neglected tropical disease caused by the bacterium Myobacterium ulcerans. The disease has been reported in at least 33 countries in Africa, South America, and the Western Pacific, according to the WHO. Buruli ulcer notably causes lesions and ulcers to occur on the skin and (less commonly) bone, leading to irreversible disfigurement and long-term disability in severe cases. Initial symptoms include painless swelling primarily of the arms and legs, which can ulcerate within 4 weeks if left untreated.

Buruli ulcers are typically treated with antibiotics, and, in some instances, surgery is also required. Antibiotic therapy, while generally effective, is expensive, long (approximately 56 days on average) and may lead to severe side effects in 25% of patients. Thus, the treatment costs can be substantial. A study found the cost per patient in Australia for recurring cases to be AU$13,372 (not including indirect costs and economic disease burden resulting from morbidity and mortality).

The WHO states that there were 2206 cases of Buruli ulcer reported worldwide in 2017; however, the actual number of cases is likely higher, since only 13 of the 33 countries regularly report the disease. Most cases occur in rural communities in sub-Saharan Africa, especially West and Central Africa in countries such as Cameroon, Cote d’Ivoire, and Ghana. Children under 15 represent nearly half of those affected in Africa.

While countries in Africa report the most number of cases, Australia represents a growing region of concern. Total cases have risen steadily since 2010, from under about 50 cases per year to 236 in 2017. The findings from a 2018 demographic study “suggest a serious change in the epidemiology of M. ulcerans disease in southeastern Australia.” These include an increase in the proportion of severe cases, particularly among patients 65 and older, and spread to new geographic areas within the sub-region. The reasons for these changes are unknown and represent a research priority for scientific and public health investigators.

Public Health Priorities

There are many unknowns about Buruli ulcers that hinder the development and implementation of targeted public health interventions. In particular, there is a need to improve understanding of the mode of transmission and risk factors for Buruli ulcers. Some evidence suggests the bacteria may be spread by aquatic insects or water-borne vectors, potentially via the respiratory tract, since endemic areas are usually associated with wetlands, swamps, or stagnant waters. However, a recent study suggests that it may be spread in Australia by possums or other mammals, which may serve as an animal reservoir, since a large percentage of possums in endemic areas were found to either have Buruli’s ulcer or harbor the M. ulcerans bacteria which causes it.  Yet other studies point to the role of mosquitoes in spreading the disease, either as a true vector or by facilitating infection via trauma into skin already contaminated with the bacteria. The distribution of lesions trends towards exposed limbs, such as arms and legs rather than hands and feet, suggesting a role for biting insects.

As for risk factors, a recent study in Togo suggests that risk factors for the disease include age less than 10 years, receiving insect bites near a river, and bathing with water from an open borehole. Another study in Ghana found that the greatest perceived risk factor for contracting the disease is “witchcraft,” thus revealing major gaps in the public’s knowledge of the disease and how to prevent it. In Australia, travel to an endemic region has been identified as the main risk factor for infection, according to Victoria’s Department of Health. To identify more specific risk factors, public health researchers will need to examine the human behavioral patterns and environmental characteristics associated with the disease. Gathering data on potential high-risk activities, such as hiking, swimming, or outdoor recreation, as well as frequency of encounters with animal species and exposure to insect bites and contaminated water sources, will help to understand the etiology of the disease. Researchers will also need to understand how case density correlates with regional land use patterns, housing development, and population movements.

Conclusion

Greater knowledge and understanding of Buruli ulcer can lead to more targeted public health interventions to prevent and limit its spread. For example, it is unknown whether social distancing techniques, limiting human contact with aquatic or mammalian sources, taking preventative measures such as wearing long sleeved clothing, or eliminating certain vectors will be viable public health strategies. Public health officials should stay alert to changing epidemiological patterns, including increasing severity, case counts, and geographic spread. Ultimately, it is hoped that the outbreak will promote greater awareness and fund research and development into the causes and prevention of Buruli ulcer, which in turn can benefit other nations and communities facing this neglected tropical disease in sub-Saharan Africa and elsewhere.

Photo: A view of Port Philip Bay overlooking Melbourne. Multiple cases of Buruli ulcer have been reported along Port Philip Bay in southeastern Australia.

Photo courtesy of Flickr / Philip Mallis

Outbreak Observatory aims to collect information on challenges and solutions associated with outbreak response and share it broadly to allow others to learn from these experiences in order to improve global outbreak response capabilities.