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Buruli ulcer specialist says surveys of wild animals are urgently required in endemic areas

28 Apr 2008

Joao Souza

Source: TropIKA

A typical Buruli ulcer on the arm of a young girl

There were plenty of reasons for celebration among the researchers brought together for the World Health Organization (WHO)’s 10th Annual Meeting on Buruli ulcer, held in Geneva, Switzerland, from 31 March to 2 April 2008.

As well as it being the 60th anniversary of the first isolation of the causative organism (Mycobacterium ulcerans) by Australian professor Peter MacCallum’s team, 2008 is also the year in which, more than a century since the first description of the disease (by British physician Sir Albert Cook in Uganda), a team of researchers has discovered a probable environmental hiding place for the bacteria.

The team, led by microbiologist Françoise Portaels, of the Institute of Tropical Medicine in Antwerp, Belgium, have reported the groundbreaking achievement in an article (1) published in PLoS NTDs – ‘First Cultivation and Characterization of Mycobacterium ulcerans from the Environment’.

Buruli ulcer (BU) is a flesh-eating disease named after a region in Uganda with a high prevalence of the infirmity; it was especially high here during the 1960s. It is the third most common human mycobacteriosis worldwide, after tuberculosis (Mycobacterium tuberculosis) and leprosy (Mycobacterium leprae).

Responsible for a necrotizing (although painless) infection of skin, subcutaneous fat and even bones – due to the bacterial release of a potent exotoxin called mycolactone – this highly incapacitating and stigmatizing disease has been reported in 30 countries. Most of these countries are situated in the tropical and sub-tropical regions of the world and it is mainly poor rural communities that are affected. There are high levels of clinical sub-notification and misdiagnosis.

Although there already have been associations between endemic areas and stagnant water bodies – such as slow flowing rivers, reservoirs and swamps – scientists have not until now managed to isolate well-characterized pure cultures of Mycobacterium ulcerans directly from the environment. There have been cultures made from wound collected material, but with very slow growing results.

In their PLoS NTDs article, Portaels’ team presents details of the isolation and characterization of a M. ulcerans strain obtained from an aquatic insect from Benin, Gerris sp, popularly known as ‘water strider’ or ‘Jesus bug’ – due to its ability to exploit surface tension to walk on top of ponds without sinking.

Gerris sp popularly known as Water Strider or Jesus Bug

According to the authors, this unprecedented culture isolation supports the concept that the agent of BU is a human pathogen with an environmental niche. It is a milestone achievement, especially for Portaels, who has been dealing with BU for nearly four decades beginning with her Congo experience as a PhD student in 1970.

After isolation from the bugs, the cultures were inoculated into the paws of mice, which developed progressive infection and lesions with similar histopathological features to those described in humans infected with M. ulcerans.

It is important that the recent findings are put into perspective. The insect does not bite humans, so it cannot be responsible for direct transmission of BU or act as a vector. It may play the role of an intermediate host in the infectious cycle of the disease.

Nevertheless, the article was a significant contribution to the general discussion that took place at the WHO 10th Annual Meeting on BU, alongside discussions concerning to other important issues related to the disease, as the need for earlier diagnosis and faster and more effective treatments. Following the Geneva meeting, Dr Françoise Portaels talked to TropIKA.net.

TropIKA: What are the main lessons learned from this research?

Dr Françoise Portaels: First of all that we need to improve cultivation of M. ulcerans from the environment. The techniques we have used to obtain a pure culture of M. ulcerans from the environment are fastidious and need to be simplified. As one of the researchers said in her comments/ratings for our article, ‘The effort it took to show this organism really is the pathogen of BU is truly herculean’. We will try therefore to resuscitate M. ulcerans present in the environment under a VBNC (viable but nonculturable) state using other techniques described in the literature to resuscitate environmental microorganisms. The role of free-living amoebae in the reservoir and transmission of M. ulcerans will be explored. We will also use other culture media including selective media containing specific antibiotics to inhibit other environmental mycobacteria and obtain pure culture of M. ulcerans.

TropIKA: Are you planning to focus only on insects? What about searching for Buruli ulcer in other vertebrates?

Dr Françoise Portaels: Whether wild animals may be reservoirs of M. ulcerans and play a role in the transmission of BU is an important question that, to date, has not been fully explored. In 2001, we published a paper on M. ulcerans in wild animals and stated that surveys of wild animals are urgently required in those areas in which BU is endemic (2). During last WHO meeting on BU in Geneva, Australian researchers presented their findings on wild animals in Australia (3).

TropIKA: Could you tell us a little bit more about that particular study?

Dr Françoise Portaels: They have developed a new hypothesis to explain the focal nature of BU outbreaks in coastal Victoria. According to these authors, M. ulcerans initially colonizes and spreads among possums (small arboreal marsupials) and humans may become infected through transmission via mosquitoes. They will investigate this new hypothesis by analyzing possums in endemic areas in 2008. Similarly, we plan to investigate wild vertebrates in BU endemic and non endemic areas in Benin, Ghana and the Democratic Republic of Congo.

TropIKA: Are there any particular species on target?

Dr Françoise Portaels: The high virulence for mice of the environmental M. ulcerans isolate suggests the possibility of high virulence for rodents. Based on this hypothesis, wild rodents from both highly endemic as well as non-endemic areas for BU will be captured to investigate if the disease can also be pathogenic for vertebrates other than humans.

TropIKA: Are this study going to be supported by any specific grant?

Dr Françoise Portaels: Our activities will be partly supported by a grant from the Flemish University Council (VLIR-UOS), Belgium.

TropIKA: What is still the major hurdle in the way of BU’s elimination or even eradication?

Dr Françoise Portaels: Buruli ulcer is thus a disease strongly associated with natural environments. BU is rarely, if ever, contagious. However, the eradication of a disease with environmental reservoir(s) is extremely complicate. Our article in PLoS NTDs on the first isolation and characterization of M. ulcerans from an environmental source has confirmed that M. ulcerans is present in viable form in the aquatic environment. Many epidemiological reports have shown that BU outbreaks are related to the proximity of slowly flowing waters or swamps (4,5,6) We have demonstrated that the use of unprotected water for domestic purposes, swimming and wading in slow flowing rivers are important risk factors for M. ulcerans disease (7,8). Moreover, the occurrence of the disease in hosts other than humans will not facilitate the task.

TropIKA: Meanwhile, what cost-effect measures could be done to help curbing the burden of this severely stigmatizing disease?

Dr Françoise Portaels: Preventions tools may be developed to decrease the frequency of the disease. In an endemic tropical rural setting where children usually are scantily attired, prevention of contamination of the skin from environmental sources is virtually impossible. Wearing trousers seems to prevent development of infection. Protected water supplies in villages would reduce exposure somewhat (9); however, such protective measures include: frequent use of soap for washing, treating injuries with soap and/or application of antibiotic powder, contact with rapid flowing water, use of bed nets and insect repellent (7,8). Vaccination may be another prevention tool.

TropIKA: When you say vaccination, do you refer to BCG?

Dr Françoise Portaels: Not only. Vaccination with BCG has a moderate protective effect against M. ulcerans infections for 6 to 12 months. BCG vaccination has a prophylactic effect against osteomyelitis in Buruli ulcer (10). The protective effect against BU of BCG vaccination at birth could not be confirmed by two recent case-control studies (3,11). Other vaccines based on DNA engineering and virulence factors of M. ulcerans (e.g., the toxin) are being studied.

TropIKA: And what about the use of the so-called ‘French clay’ (a soil mineral mud with allegedly antibiotic effects). Could it be also included among the other prevention tools? Or does it still lack scientific evidence?

Dr Françoise Portaels: I didn’t mention French clay because it is a treatment and not a prevention tool. I am pleased you asked me this question because the person who used it in Côte d’Ivoire, Line de Courssou, was one of my best friends. Unfortunately she passed away in 2006. She was a nurse and did a very nice work which was not enough recognized by the international community. (Line Brunet de Courssou, was a French humanitarian who first described the clay’s therapeutic effect on Buruli ulcer in 2002). She successfully treated some BU patients with only clay and very careful nursing. These patients were cured without large excisions.

TropIKA: Are there any other alternative therapies for BU under study that were discussed during the Geneva meeting?

Dr. Françoise Portaels: It is possible to cure some patients with other treatments than surgery or antibiotics. Heat therapy can also successfully cure patients with early lesions. There was a nice presentation on heat therapy by Dr T Junghans et al. who treated patients in Cameroon without surgery – only with heat therapy.

Dr Françoise Portaels (seated with pink scarf) and staff of Institute of Tropical Medicine in Antwerp, Belgium

Reference

Portaels F, Meyers WM, Ablordey A, Castro AG, Chemlal K, et al. ( First Cultivation and Characterization of Mycobacterium ulcerans from the Environment. PLoS Negl Trop Dis 2008; 2(3): e178. doi:10.1371/journal.pntd.0000178
Portaels F, Chemlal K, Elsen P, Johnson PDR, Hayman JA, Kirkwood R, Meyers WM. Mycobacterium ulcerans in wild animals. In: Mycobacterial infections in domestic and wild animals. Office International de Epizooties. Scientific and Technical Review. Paris. Ed. Collins MT, Manning B. 2001; 20: 252-264.
Johnson P, Fyfe J, Lavender C, Stinear T, Azuolas J, Jenkin G, O’Brien C, McCowan C, Brown L, Hayman J. From golf courses to possum traps – a 10 year review of the epidemiology of Buruli ulcer in Victoria, Australia. WHO Annual Meeting on Buruli ulcer, Geneva, Switzerland, 31.03 – 02.04.2008. Abstract book pp 16-17.
Debacker M, Aguiar J, Steunou C, Zinsou C, Meyers WM, Guédénon A, Scott JT, Dramaix M, Portaels F. Mycobacterium ulcerans Disease (Buruli ulcer) in a Rural Hospital, Southern Benin, 1997-2001. Emerg Infect Dis 2004; 10: 1391-1398.
Debacker M, Portaels F, Aguiar J, Steunou C, Zinsou C, Meyers W, Dramaix M. Risk factors for Buruli ulcer, Benin. Emerg Infect Dis 2006; 12: 1325-1331.
Sizaire V, Nackers F, Comte E, Portaels F. Mycobacterium ulcerans infection: control, diagnosis, and treatment. Lancet Infect Dis 2006; 6: 288-296.
Pouillot R, Matias G, Mbondji Wondje C, Portaels F, Valin N, Ngoss F, Njikap A, Marsollier L, Fontanet A, Eyangoh S. Risk factors for Buruli ulcer disease in Cameroon. PloS Negl Trop Dis 2007; 1: e101.
Nackers F, Johnson RC, Glynn J, Zinsou C, Tonglet R, Portaels F. Environmental and health-related risk factors for Mycobacterium ulcerans disease (Buruli ulcer) in Benin. Amer J Trop Med Hyg 2007; 77: 834-836.
Johnson RC, Makoutodé M, Sopoh GE, Elsen P, Gbovi J, Pouteau LH, Meyers WM, Boko M, Portaels F. Buruli ulcer distribution in Benin. Emerg Infect Dis 2005; 11: 500-501.
Portaels F, Aguiar J, Debacker M, Guédénon A, Steunou C, Zinsou C, Meyers WM. BCG vaccination as prophylaxis against Mycobacterium ulcerans osteomyelitis in Buruli ulcer disease. Infect Immun 2004; 72: 62-65.
Nackers F, Dramaix M, Johnson RC, Zinsou C, Robert A, de Biurrun Bakedano E, Glynn JR, Portaels F, Tonglet R. BCG vaccine effectiveness against Mycobacterium ulcerans disease (Buruli ulcer): A case-control study in Benin. Amer J Trop Med Hyg 2006; 75: 768-774.