Mycobacterium ulcerans in wild animals

Mycobacterium ulcerans infection, or Buruli ulcer, is the third most freque nt mycobacterial disease in humans, often causing serious deformities and d isability. The disease is most closely associated with tropical wetlands, e specially in west and central Africa. Most investigators believe that the a etiological agent proliferates in mud beneath stagnant waters. Modes of tra nsmission may involve direct contact with the contaminated environment, aer osols from water surfaces, and water-dwelling fauna (e.g. insects). Person- to-person transmission is rare. Trauma at the site of skin contamination by M. ulcerans appears to play an important role in initiating disease. Once introduced into the skin or subcutaneous tissue, M. ulcerans multiplies and produces a toxin that causes necrosis. However, the type of disease induce d varies from a localised nodule or ulcer,to widespread ulcerative or non-u lcerative disease and osteomyelitis. Although culture of M. ulcerans from a patient was first reported in 1948, attempts to culture the mycobacterium from many specimens of flora and faun a have been unsuccessful. Failure to cultivate this organism from nature ma y be attributable to inadequate sampling, conditions of transport, decontam ination and culture of this fastidious heat-sensitive organism, and to a lo ng generation time relative to that of other environmental mycobacteria. Ne vertheless, recent molecular studies using specific primers have revealed M . ulcerans in water, mud, fish and insects. Although no natural reservoir h as been found, the possibility that M. ulcerans may colonise microfauna suc h as free-living amoebae has not been investigated. The host range of experimental infection by M. ulcerans includes lizards, a mphibians, chick embryos, possums, armadillos, rats, mice and cattle. Natur al infections have been observed only in Australia, in koalas, ringtail pos sums and a captive alpaca. The lesions were clinically identical to those o bserved in humans. Mycobacterium ulcerans infection is a rapidly re-emergin g disease in some developing tropical countries. The re-emergence may be re lated to environmental and socioeconomic factors, for example, deforestatio n leading to increased flooding, and population expansion without improved agricultural techniques, th us putting more people at risk. Eradication of diseases related to these factors is difficult. Whether wild animals have a role in transmission is an important question that, to date, has been virt ually unexplored. To address this question, surveys of wild animals are urg ently required in those areas in which Buruli ulcer is endemic.