Trends in Microbiology
Volume 15, Issue 8, August 2007, Pages 338-339
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Protozoa as an environmental reservoir of bovine tuberculosis

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An issue for the epidemiology of bovine tuberculosis?

The route of infection of cattle with Mycobacterium bovis is not entirely understood. It is suspected that climate has some role in the epidemiology of bovine tuberculosis in Britain 1, 2, and local climatic features that enable prolonged survival of M. bovis on pasture could be important in determining the survival and subsequent transmission of M. bovis to cattle. Soil microorganisms form part of the local environment for M. bovis, particularly at badger and cattle watering hole or latrine

Consider the protozoa

Protozoa are unicellular organisms that represent one of the oldest forms of animal life. They have become adapted to almost all types of environment, the availability of food and water being the most important factors governing their prevalence in different micro-environments. Few protozoa can synthesize their food from inorganic materials and they therefore depend upon available organic substances such as disintegrating plant or animal material or, relevant here, living microorganisms. Hence,

Association of free-living protozoa with pathogenic bacteria

Free-living protozoa are known to occur concurrently with pathogenically important bacteria. These predatory protozoa graze on bacterial biofilms in the environment as a food source. Some bacteria, however, are resistant to killing by protozoa. This intra-amoebic survival of bacterial pathogens and use of the amoebic cyst to avoid environmental stress and aid dissemination has highlighted the protozoa as the Trojan Horses of the bacterial world [4]. Importantly, these relationships between

A natural host model for M. bovis

Mycobacteria are ubiquitous in aquatic environments, where they have been linked to several water-borne diseases including Mycobacterium marinum granulomas, Mycobacterium kansasii-associated rheumatoid-like syndromes of the wrist, hand and synovial joints, and Mycobacterium avium infection of AIDS patients. M. avium, Mycobacterium a. paratuberculosis and Mycobacterium leprae can survive and replicate within amoebae. Furthermore, the intra-amoebic survival of non-tuberculous mycobacteria within

Concluding remarks

Free-living protozoa have been shown to aid the survival and persistence of numerous pathogenic bacterial species. The possibility that this might also apply to mycobacterial pathogens is receiving increased attention. Here, we have highlighted the potential importance of protozoa to M. bovis, the agent of bovine tuberculosis, first as an environmental reservoir and second as a relevant host cell for laboratory investigation. In terms of the epidemiology of bovine tuberculosis, a role for

Acknowledgements

We thank Cornelia Mardare (University of Surrey) and Glyn Hewinson (VLA) for their helpful comments and discussion. S.G.R. is funded by the Department for Environment, Food and Rural Affairs (DEFRA), UK.

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