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Environmental mycobacteria in northern Malawi: implications for the epidemiology of tuberculosis and leprosy

Published online by Cambridge University Press:  16 July 2001

P. E. M. FINE
Affiliation:
Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT
S. FLOYD
Affiliation:
Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT
J. L. STANFORD
Affiliation:
Department of Medical Microbiology, Royal Free and University College Medical School, Windeyer Institute of Medical Sciences, 46 Cleveland Street, London W1P 6DB
P. NKHOSA
Affiliation:
Karonga Prevention Study, PO Box 46, Chilumba, Karonga District, Malawi
A. KASUNGA
Affiliation:
Karonga Prevention Study, PO Box 46, Chilumba, Karonga District, Malawi
S. CHAGULUKA
Affiliation:
Karonga Prevention Study, PO Box 46, Chilumba, Karonga District, Malawi
D. K. WARNDORFF
Affiliation:
Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT Karonga Prevention Study, PO Box 46, Chilumba, Karonga District, Malawi
P. A. JENKINS
Affiliation:
Bryn Glas, Llangcitho, nr Tregaron, Cardiganshire SY25 6TR, UK
M. YATES
Affiliation:
Mycobacterial Reference Laboratory, Kings College Hospital (Dulwich), East Dulwich Grove, London SE22 8QF
J. M. PONNIGHAUS
Affiliation:
Karonga Prevention Study, PO Box 46, Chilumba, Karonga District, Malawi Pappelweg 08548 Syrau Germany
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Abstract

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More than 36000 individuals living in rural Malawi were skin tested with antigens derived from 12 different species of environmental mycobacteria. Most were simultaneously tested with RT23 tuberculin, and all were followed up for both tuberculosis and leprosy incidence. Skin test results indicated widespread sensitivity to the environmental antigens, in particular to Mycobacterium scrofulaceum, M. intracellulare and one strain of M. fortuitum. Individuals with evidence of exposure to ‘fast growers’ (i.e. with induration to antigens from fast growers which exceeded their sensitivity to tuberculin), but not those exposed to ‘slow growers’, were at reduced risk of contracting both tuberculosis and leprosy, compared to individuals whose indurations to the environmental antigen were less than that to tuberculin. This evidence for cross protection from natural exposure to certain environmental mycobacteria may explain geographic distributions of mycobacterial disease and has important implications for the mechanisms and measurement of protection by mycobacterial vaccines.

Type
Research Article
Copyright
© 2001 Cambridge University Press