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Buruli Ulcer: Advances in Understanding Mycobacterium ulcerans Infection

      Keywords

      Buruli ulcer (BU), the third most common mycobacterial infection in humans next to tuberculosis and leprosy, is an emerging infection caused by Mycobacterium ulcerans. BU is characterized by indolent, typically painless necrotizing skin lesions (Figs. 1 and 2A). Approximately 10% of patients develop bone involvement subjacent to skin lesions or metastatic osteomyelitis from lymphohematogenous spread of M ulcerans (see Fig. 2B). Pathogenesis is mediated by mycolactone, a diffusible, necrotizing, immunosuppressive, polyketide-derived macrolide toxin secreted by M ulcerans.
      • Silva M.T.
      • Portaels F.
      • Pedrosa J.
      Pathogenetic mechanisms of the intracellular parasite Mycobacterium ulcerans leading to Buruli ulcer.
      In 1962, the disease was named after Buruli County, Uganda, now called Nakasongola District, where the epidemic was documented first. Other names include Bairnsdale, Kakerifu, Kasongo, or Searls' ulcer.
      Figure thumbnail gr1
      Fig. 1Plaque of BU on the right flank of a Ghanaian boy. The lesion has characteristic rolled borders and is remarkably stellate, a feature of some plaques.
      Figure thumbnail gr2
      Fig. 2(A) Plaque of BU on the forearm of a Congolese boy invaded the deep tissues and bone, causing contiguous osteomyelitis. (B) Radiograph shows contiguous reactive osteitis and necrosis of the cortex of the radius, with formation of a large sequestrum (arrow).

      Epidemiology

      In 1998, the World Health Organization (WHO) recognized BU as a reemerging infectious disease in West and Central Africa, with a significant public health impact.
      • World Health Organization
      Buruli ulcer progress report, 2004–2008.
      The reported incidence rates of BU are highest in West Africa, especially Benin, Ghana, and Côte d’Ivoire. However, BU is reported in about 30 countries (Fig. 3), and growing evidence suggests that BU is more widespread than earlier thought.
      • Walsh D.S.
      • Eyase F.
      • Onyango D.
      • et al.
      Short report: clinical and molecular evidence for a case of Buruli ulcer (Mycobacterium ulcerans infection) in Kenya.
      BU prevails in rural tropical wetlands, especially areas with stagnant water, including ponds and swamps. However, BU is also acquired without wetland exposure.
      Figure thumbnail gr3
      Fig. 3Distribution of BU by country, as of 2010. Relative endemicity is denoted as high (red), moderate (yellow), and low (green); asterisks denote countries with suspected cases. Imported BU is occasionally diagnosed in the United States, Canada, and Europe.
      The rapid reemergence of BU, beginning in the early 1980s, particularly in areas where people are engaged in manual agriculture in wetlands, may be attributable to the man-made alterations to the environment, such as deforestation and other topographic alterations, which increase the amount of wetlands. Changes in global temperature and precipitation patterns further promote the reemergence of BU.
      The WHO reports indicate that more than 5000 people are diagnosed with BU annually, but many cases are undiagnosed because of the geopolitical and socioeconomic factors in endemic countries. Children (5–15 years old) have the highest incidence of BU, with most lesions on the lower extremities. BU is a growing public health problem, with psychosocial and socioeconomic implications in endemic regions. Up to 60% of patients with BU suffer from disabling and stigmatizing sequelae, including scarring, contractures, and bone destruction.
      • Barogui Y.
      • Johnson R.C.
      • van der Werf T.S.
      • et al.
      Functional limitations after surgical or antibiotic treatment for Buruli ulcer in Benin.
      Minimizing disability through treatment, both antimicrobial and surgical, and physiotherapy is, therefore, important in BU management. Imported BU is occasionally diagnosed in the United States, Canada, and Europe.
      • McGann H.
      • Stragier P.
      • Portaels F.
      • et al.
      Buruli ulcer in United Kingdom tourist returning from Latin America.
      BU is directly related to environmental factors and thus considered noncontagious.
      • Portaels F.
      • Silva M.T.
      • Meyers W.M.
      Buruli ulcer.
      The most possible mode of transmission is local, minor, often unnoticed skin trauma that permits inoculation of M ulcerans. The estimated incubation period is 2 to 3 months. Because M ulcerans DNA is detectable in some aquatic insects, the role of insects as vectors that infect humans by biting is under investigation.
      • Marion E.
      • Eyangoh S.
      • Yeramian E.
      • et al.
      Seasonal and regional dynamics of M. ulcerans transmission in environmental context: deciphering the role of water bugs as hosts and vectors.
      In Australia, some investigators propose that BU is a zoonosis transmitted by mosquitoes from indigenous marsupials (eg, possums and koalas) to humans. M ulcerans DNA was found in mosquitoes during an outbreak of BU in humans in Australia, and the seasonal incidence of BU in humans correlates with that of notifiable arthropod-borne diseases in Victoria.
      • Johnson P.D.
      • Lavender C.J.
      Correlation between Buruli ulcer and vector-borne notifiable diseases, Victoria, Australia.
      In Africa, terrestrial mammals are being investigated as reservoirs of M ulcerans.
      • Durnez L.
      • Suykerbuyk P.
      • Nicolas V.
      • et al.
      The role of terrestrial small mammals as reservoir of Mycobacterium ulcerans in Benin.
      Risk factors for BU within endemic areas include failure to wear protective clothing, exposure to unprotected natural water sources, and inadequate care of minor skin wounds.
      • Jacobsen K.H.
      • Padgett J.J.
      Risk factors for Mycobacterium ulcerans infection.
      • Sopoh G.E.
      • Barogui Y.T.
      • Johnson R.C.
      • et al.
      Family relationship, water contact and occurrence of Buruli ulcer in Benin.
      Human immunodeficiency virus seropositivity may increase the risk for BU or be associated with aggressive BU.
      • Johnson R.C.
      • Nackers F.
      • Glynn J.R.
      • et al.
      Association of HIV infection and Mycobacterium ulcerans disease in Benin.
      BCG vaccination has some effect on BU. Several reports suggest that BCG vaccination provides some protection against BU, for 6 to 12 months after vaccination, and that neonatal BCG vaccination reduces the risk of BU osteomyelitis in those who acquire BU as children or adults.
      • Portaels F.
      • Aguiar J.
      • Debacker M.
      • et al.
      Mycobacterium bovis BCG vaccination as prophylaxis against Mycobacterium ulcerans osteomyelitis in Buruli ulcer disease.
      • Smith P.G.
      • Revill W.D.
      • Lukwago E.
      • et al.
      The protective effect of BCG against Mycobacterium ulcerans disease: a controlled trial in an endemic area of Uganda.
      • Portaels F.
      • Aguiar J.
      • Debacker M.
      • et al.
      Prophylactic effect of Mycobacterium bovis BCG vaccination against osteomyelitis in children with Mycobacterium ulcerans disease (Buruli ulcer).
      However, a case-control study concluded that BCG vaccination is not protective against BU.
      • Nackers F.
      • Dramaix M.
      • Johnson R.C.
      • et al.
      BCG vaccine effectiveness against Buruli ulcer: a case-control study in Benin.
      Prophylactic and therapeutic vaccines based on DNA engineering and virulence factors, including mycolactone, are under study (BuruliVac Project).
      • Huygen K.
      • Adjei O.
      • Affolabi D.
      • et al.
      Buruli ulcer disease: prospects for a vaccine.
      Intravenous immunoglobulin to neutralize mycolactone is not available.

      Microbiology of M ulcerans

      Standard and real-time polymerase chain reaction (PCR) techniques have been used to identify M ulcerans, primarily by detecting 2 M ulcerans insertion sequences (IS2404 and IS2606), in the environment in Australia and West Africa.
      • Vandelannoote K.
      • Durnez L.
      • Amissah D.
      • et al.
      Application of real-time PCR in Ghana, a Buruli ulcer-endemic country, confirms the presence of Mycobacterium ulcerans in the environment.
      Improved M ulcerans DNA extraction procedures enhance environmental detection, thereby advancing the understanding of reservoirs.
      • Durnez L.
      • Stragier P.
      • Roebben K.
      • et al.
      A comparison of DNA extraction procedures for the detection of Mycobacterium ulcerans, the causative agent of Buruli ulcer, in clinical and environmental specimens.
      Portaels and colleagues
      • Portaels F.
      • Meyers W.M.
      • Ablordey A.
      • et al.
      First cultivation and characterization of Mycobacterium ulcerans from the environment.
      reported the first direct isolation of M ulcerans from nature in 2008 from a water strider, an aquatic insect that does not bite humans.
      Unlike M leprae and M tuberculosis (the pathogens for leprosy and tuberculosis, respectively), M ulcerans produces a necrotizing, immunosuppressive, polyketide-derived macrolide toxin, called mycolactone.
      • Silva M.T.
      • Portaels F.
      • Pedrosa J.
      Pathogenetic mechanisms of the intracellular parasite Mycobacterium ulcerans leading to Buruli ulcer.
      Genes in a virulence plasmid of M ulcerans, controlled by SigA-like promoters,
      • Tobias N.J.
      • Seemann T.
      • Pidot S.J.
      • et al.
      Mycolactone gene expression is controlled by strong SigA-like promoters with utility in studies of Mycobacterium ulcerans and Buruli ulcer.
      encode for the synthesis of mycolactone. Identification of SigA-like promoters led to the development of M ulcerans–green fluorescent protein. This tagged protein linking fluorescence with toxin gene expression is a potential tool for studying BU pathogenesis and transmission.
      • Tobias N.J.
      • Seemann T.
      • Pidot S.J.
      • et al.
      Mycolactone gene expression is controlled by strong SigA-like promoters with utility in studies of Mycobacterium ulcerans and Buruli ulcer.
      M ulcerans shares some environmental, molecular, and clinical features with M marinum, a water-associated organism that causes granulomatous skin lesions in humans, often called “swimming pool” or “fish tank” granuloma. Comparative genomics indicate that M ulcerans likely diverged from M marinum, acquiring a 174-kb virulence plasmid (pMUM001) with genes coding for mycolactone production and 10 proteins, all potential targets for vaccine development or serodiagnosis.
      • Demangel C.
      • Stinear T.P.
      • Cole S.T.
      Buruli ulcer: reductive evolution enhances pathogenicity of Mycobacterium ulcerans.
      Accordingly, phenolic mycosides of M ulcerans and M marinum are identical, and sequences for the 16S ribosomal RNA (rRNA) gene are nearly identical.
      • Portaels F.
      • Silva M.T.
      • Meyers W.M.
      Buruli ulcer.
      As M ulcerans evolved toward becoming an intracellular organism, like M marinum, nonessential genes were lost, which may have increased the pathogenicity.
      • Demangel C.
      • Stinear T.P.
      • Cole S.T.
      Buruli ulcer: reductive evolution enhances pathogenicity of Mycobacterium ulcerans.
      Gene sequences of the 3′ end of the 16S rRNA of M ulcerans vary by geographic origin, dividing M ulcerans broadly into African, American, Asian, and Australian strains, with many substrains on each continent.
      • Stragier P.
      • Ablordey A.
      • Bayonne L.M.
      • et al.
      Heterogeneity among Mycobacterium ulcerans isolates from Africa.
      Each major strain generally differs in clinical presentation, mycolactone type and virulence, and host immune responses.
      • Ortiz R.H.
      • Leon D.A.
      • Estevez H.O.
      • et al.
      Differences in virulence and immune response induced in a murine model by isolates of Mycobacterium ulcerans from different geographic areas.
      Mycolactone type coding by geographic origin includes A/B (Africa, the most pathogenic), C (Asia, Australia), and D (Asia).
      • Silva M.T.
      • Portaels F.
      • Pedrosa J.
      Pathogenetic mechanisms of the intracellular parasite Mycobacterium ulcerans leading to Buruli ulcer.
      Molecular genetic techniques are slowly unraveling the evolution of M ulcerans. M ulcerans isolates from localized foci within endemic regions often show a high degree of genomic similarity (ie, clonal populations) with a lack of insertional-deletional genomic polymorphisms, underscoring a requirement for single-nucleotide polymorphism (SNP) analysis to differentiate substrains of M ulcerans within those areas.
      • Kaser M.
      • Gutmann O.
      • Hauser J.
      • et al.
      Lack of insertional-deletional polymorphism in a collection of Mycobacterium ulcerans isolates from Ghanaian Buruli ulcer patients.
      Identifying SNPs and establishing SNP typing assays are increasingly defining the microepidemiology, genetic diversity, and evolution of M ulcerans.
      • Kaser M.
      • Hauser J.
      • Pluschke G.
      Single nucleotide polymorphisms on the road to strain differentiation in Mycobacterium ulcerans.
      • Qi W.
      • Kaser M.
      • Roltgen K.
      • et al.
      Genomic diversity and evolution of Mycobacterium ulcerans revealed by next-generation sequencing.
      For example, SNP analyses of M ulcerans in Ghana differentiate 54 M ulcerans strains into 13 SNP haplotypes, yet a geographically focal transmission.
      • Qi W.
      • Kaser M.
      • Roltgen K.
      • et al.
      Genomic diversity and evolution of Mycobacterium ulcerans revealed by next-generation sequencing.
      • Roltgen K.
      • Qi W.
      • Ruf M.T.
      • et al.
      Single nucleotide polymorphism typing of Mycobacterium ulcerans reveals focal transmission of Buruli ulcer in a highly endemic region of Ghana.

      Pathogenesis and immunity

      Initial infection is primarily related to 2 properties of M ulcerans: optimal growth at temperatures (30°C–33°C) slightly below the core body temperature and production of mycolactone. The temperature requirement of M ulcerans favors the development of lesions in cooler tissues, especially the skin and subcutaneous tissue. Mycolactone destroys tissues by apoptosis and necrosis (Fig. 4) and suppresses host immune responses.
      • Silva M.T.
      • Portaels F.
      • Pedrosa J.
      Pathogenetic mechanisms of the intracellular parasite Mycobacterium ulcerans leading to Buruli ulcer.
      Figure thumbnail gr4
      Fig. 4Microscopic section of the undermined edge of a major BU. Note contiguous coagulation necrosis of the panniculus and fascia and vasculitis with thrombosis of a medium-sized vessel (arrow) (hematoxylin-eosin, original magnification ×40). A mild host inflammatory response is consistent with a toxin-mediated process.
      Mycolactone profoundly suppresses elements of innate and adaptive cell-mediated immunity, thereby enhancing progression of BU. Mycolactone inhibits macrophages, monocytes, B cells, and T cells at least, in part, by inhibiting production of interleukin (IL)-1, IL-2, IL-6, IL-8, IL-10, tumor necrosis factor α, and interferon-γ (IFN-γ).
      • Boulkroun S.
      • Guenin-Mace L.
      • Thoulouze M.I.
      • et al.
      Mycolactone suppresses T cell responsiveness by altering both early signaling and posttranslational events.
      • Torrado E.
      • Fraga A.G.
      • Logarinho E.
      • et al.
      IFN-gamma-dependent activation of macrophages during experimental infections by Mycobacterium ulcerans is impaired by the toxin mycolactone.
      The immunosuppressive effects of mycolactone extend beyond skin lesions to circulating leukocytes and lymphoid organs.
      • Hong H.
      • Coutanceau E.
      • Leclerc M.
      • et al.
      Mycolactone diffuses from Mycobacterium ulcerans-infected tissues and targets mononuclear cells in peripheral blood and lymphoid organs.
      Peripheral whole-blood samples from patients with active BU, when stimulated with mitogens, produce comparatively smaller amounts of helper T cell (TH) 1, TH2, and TH17 cytokines.
      • Phillips R.
      • Sarfo F.S.
      • Guenin-Mace L.
      • et al.
      Immunosuppressive signature of cutaneous Mycobacterium ulcerans infection in the peripheral blood of patients with Buruli ulcer disease.
      The clinical and histopathologic features of BU suggest an immunologic spectrum of host responses over time, which may be relevant for vaccine strategies. Early progressive ulcers generate abundant IL-10 with little inflammation (TH2 response) and numerous, often extracellular, M ulcerans (Fig. 5) within areas of coagulation necrosis. Necrosis reflects mycolactone-induced death of tissue and inflammatory cells. In contrast, mature or resolving BU lesions, especially under treatment with antibiotics, contain IFN-γ within granulomatous inflammation, organizing lymphoid aggregates, and typically intracellular M ulcerans, consistent with a TH1, delayed-type hypersensitivity (DTH) response.
      • Silva M.T.
      • Portaels F.
      • Pedrosa J.
      Pathogenetic mechanisms of the intracellular parasite Mycobacterium ulcerans leading to Buruli ulcer.
      • Kiszewski A.E.
      • Becerril E.
      • Aguilar L.D.
      • et al.
      The local immune response in ulcerative lesions of Buruli disease.
      • Schutte D.
      • Pluschke G.
      Immunosuppression and treatment-associated inflammatory response in patients with Mycobacterium ulcerans infection (Buruli ulcer).
      DTH in these patients, but not those with early BU or uninfected persons, is verified by skin test reactivity against burulin, a sonicate of M ulcerans.
      • Stanford J.L.
      • Revill W.D.
      • Gunthorpe W.J.
      • et al.
      The production and preliminary investigation of Burulin, a new skin test reagent for Mycobacterium ulcerans infection.
      Minor BU may self-heal early, suggesting elements of high host resistance.
      Figure thumbnail gr5
      Fig. 5Microscopic section of early nodule of BU showing clumps of extracellular acid-fast bacilli (AFB, red) in the center of widespread necrosis (Ziehl-Neelsen stain, original magnification ×40). Necrosis extends far beyond the AFB, supporting the notion that M ulcerans produces a diffusible necrotizing toxin.

      Clinical features and diagnosis

      BU presents as a spectrum of localized or disseminated clinical forms, with variable natural history (Fig. 6). Early lesions are usually papular, nodular, or edematous, progressing to ulcers with rolled borders, spreading laterally. Most ulcers are painless unless secondarily infected. Fever and lymphadenopathy are rare. Experienced workers may correctly diagnose some BU lesions on clinical features alone, but there is often discord between clinical impression and laboratory results because of incorrect clinical diagnosis, inadequate sampling, or laboratory errors. Important entities in the differential diagnosis of ulcerative and edematous BU include tropical phagedenic ulcer and necrotizing fasciitis, respectively.
      • Phanzu M.D.
      • Bafende A.E.
      • Imposo B.B.
      • et al.
      Under-treated necrotizing fasciitis masquerading as ulcerated edematous Mycobacterium ulcerans infection (Buruli ulcer).
      Both these conditions, unlike BU, are painful. Many other conditions resemble BU, underscoring the importance of laboratory confirmation. Radiographic examination is indicated when bone involvement is suspected.
      Figure thumbnail gr6
      Fig. 6Proposed classification and natural history of untreated clinical forms of active BU.
      The 4 diagnostic laboratory tests for BU are (1) direct smear (with acid-fast stains auramine O or Ziehl-Neelsen), (2) culture, (3) histopathology, and (4) PCR. Estimated sensitivities for these techniques range from 60% or lesser to more than 90%. PCR, currently available only in research laboratories, is considered the most reliable method for all lesion subtypes,
      • Beissner M.
      • Herbinger K.H.
      • Bretzel G.
      Laboratory diagnosis of Buruli ulcer disease.
      followed by histopathology, culture, and direct smear. Lesion sampling techniques include swabbing, punch biopsy, and, as a less-invasive alternative to biopsy, fine-needle aspiration (FNA). PCR is highly sensitive when applied to swabbed material from ulcers and to biopsies and FNAs of nonulcerative lesions.
      • Herbinger K.H.
      • Adjei O.
      • Awua-Boateng N.Y.
      • et al.
      Comparative study of the sensitivity of different diagnostic methods for the laboratory diagnosis of Buruli ulcer disease.
      The targets of PCR, IS2404 and IS2606, may be present in other pathogenic mycobacteria, such as M marinum; so clinical features or variable number of tandem repeat assays may discriminate M ulcerans from other species.
      • Stragier P.
      • Ablordey A.
      • Durnez L.
      • et al.
      VNTR analysis differentiates Mycobacterium ulcerans and IS2404 positive mycobacteria.
      Among the non-PCR diagnostic methods, histopathology is useful to confirm BU or generate a differential diagnosis when unconfirmed. Culture is recommended for tracking treatment response, often a concern in clinical trials.
      • Herbinger K.H.
      • Adjei O.
      • Awua-Boateng N.Y.
      • et al.
      Comparative study of the sensitivity of different diagnostic methods for the laboratory diagnosis of Buruli ulcer disease.
      Pharmacologic assays to detect mycolactone in the tissues infected with M ulcerans may become a diagnostic adjunct to culture.
      • Sarfo F.S.
      • Phillips R.O.
      • Rangers B.
      • et al.
      Detection of mycolactone A/B in Mycobacterium ulcerans-infected human tissue.
      Direct smears are useful at the community level. Rapid diagnostic tests for use in the field, to detect mycolactone or M ulcerans–specific proteins in lesional or other biologic fluids, are in early development.
      Regardless of the test or sampling method, at least 2 sites per lesion suspicious for BU should be sampled; this process increases sensitivity over a single sample by up to 25%. When confronted with possible new geographic foci of BU, confirmation by PCR and at least 1 of the other 3 tests is advised.

      Treatment

      Historically, treatment of BU has been surgical excision of the affected tissues, correction of wound defects, and, if available, rehabilitative physiotherapy. Bone and joint lesions are given priority. By the 1970s, rifampin was known to heal most small BU lesions. However, until 2005, antibiotics remained a largely perioperative adjunctive therapy, aimed at reducing dissemination and recurrence or minimizing tissue excision.
      • O’Brien D.P.
      • Hughes A.J.
      • Cheng A.C.
      • et al.
      Outcomes for Mycobacterium ulcerans infection with combined surgery and antibiotic therapy: findings from a south-eastern Australian case series.
      The role of adjunctive antibiotic therapy for BU that is otherwise surgically excised remains unclear.
      • Schunk M.
      • Thompson W.
      • Klutse E.
      • et al.
      Outcome of patients with Buruli ulcer after surgical treatment with or without antimycobacterial treatment in Ghana.
      Other treatment methods, such as local heat, explored decades ago, may become practical as application systems are simplified.
      • Junghanss T.
      • Um Boock A.
      • Vogel M.
      • et al.
      Phase change material for thermotherapy of Buruli ulcer: a prospective observational single centre proof-of-principle trial.
      In 2004, with increasing BU incidence and limited surgical resources in Africa, supported by experimental and encouraging preliminary human data,
      • Etuaful S.
      • Carbonnelle B.
      • Grosset J.
      • et al.
      Efficacy of the combination rifampin-streptomycin in preventing growth of Mycobacterium ulcerans in early lesions of Buruli ulcer in humans.
      the WHO advocated a provisional antibiotic regimen for BU, comprising oral rifampin (10 mg/kg) plus intramuscular streptomycin (15 mg/kg), both given daily for 8 weeks under supervision.
      • World Health Organization
      Provisional guidance on the role of specific antibiotics in the management of Mycobacterium ulcerans disease (Buruli ulcer).
      Amikacin (15 mg/kg) can be substituted for streptomycin, administered intramuscularly or intravenously. Important contraindications and side effects for these drugs are described elsewhere.
      • World Health Organization
      Provisional guidance on the role of specific antibiotics in the management of Mycobacterium ulcerans disease (Buruli ulcer).
      As general guidelines, patients with lesions less than 5 cm in diameter (category I, small) receive antibiotics alone and those with lesions 5 to 15 cm in diameter (category II, moderate) receive 4 weeks of antibiotics and then undergo surgery, if necessary, followed by 4 more weeks of antibiotics. Patients with lesions more than 15 cm in diameter (category III, advanced) are treated with antibiotics for at least 1 week before surgery; the antibiotics are then continued for a total of 8 weeks. Follow-up of all patients is advised for an additional 10 months to assess for cure and complications.
      Case series studies of rifampin plus streptomycin for small and moderate BU conducted in Benin and Ghana concluded that most lesions resolve after 8 weeks of treatment.
      • Chauty A.
      • Ardant M.F.
      • Adeye A.
      • et al.
      Promising clinical efficacy of streptomycin-rifampin combination for treatment of Buruli ulcer (Mycobacterium ulcerans disease).
      • Sarfo F.S.
      • Phillips R.
      • Asiedu K.
      • et al.
      The clinical efficacy of combination of rifampin and streptomycin for treatment of Mycobacterium ulcerans disease.
      In 2010, Nienhuis and colleagues
      • Nienhuis W.A.
      • Stienstra Y.
      • Thompson W.A.
      • et al.
      Antimicrobial treatment for early, limited Mycobacterium ulcerans infection: a randomised controlled trial.
      reported the first randomized trial of rifampin plus streptomycin for early limited BU, defined as lesions of less than 6 months’ duration comprising nodules or ulcers less than 10 cm in diameter. Rifampin plus streptomycin given daily for 8 weeks, or for 4 weeks, followed by rifampin plus clarithromycin (both oral) daily for 4 weeks, all without surgery, healed BU in more than 90% of patients by 1 year. These results, coupled with experimental data in mice and a case report describing resolution of advanced BU after 8 weeks of rifampin plus clarithromycin,
      • Dossou A.D.
      • Sopoh G.E.
      • Johnson C.R.
      • et al.
      Management of Mycobacterium ulcerans infection in a pregnant woman in Benin using rifampicin and clarithromycin.
      support studies of fully oral, less-toxic regimens, such as rifampin plus clarithromycin or rifapentine plus moxifloxacin.
      • Ji B.
      • Chauffour A.
      • Robert J.
      • et al.
      Bactericidal and sterilizing activities of several orally administered combined regimens against Mycobacterium ulcerans in mice.
      For advanced BU, rifampin plus streptomycin therapy is under investigation. In a study in the Democratic Republic of Congo, 61 patients with PCR-positive ulcers (longest diameter>10 cm) were treated with daily rifampin plus streptomycin, treatment was extended to 12 weeks, and surgery was performed 4 weeks after antibiotics treatment was begun; 98% were classified as cured after 2 years.
      • Kibadi K.
      • Boelaert M.
      • Fraga A.G.
      • et al.
      Response to treatment in a prospective cohort of patients with large ulcerated lesions suspected to be Buruli ulcer (Mycobacterium ulcerans disease).
      Further studies in patients with large BU lesions, coordinated by the WHO, will aim to determine the best time for surgery within the course of antibiotics.
      In some BU lesions, treatment with antibiotics may cause temporary immune-mediated inflammation with clinical worsening, proposed as a paradoxic sign of treatment success.
      • O’Brien D.P.
      • Robson M.E.
      • Callan P.P.
      • et al.
      “Paradoxical” immune-mediated reactions to Mycobacterium ulcerans during antibiotic treatment: a result of treatment success, not failure.
      Awareness may prevent unnecessary treatment changes, reduce surgeries, and improve the accuracy of treatment trials.

      Acknowledgments

      The authors thank Siripan Phatisawad for making the map.

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