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Open Access Highly Accessed Research article

Molecular epidemiology and transmission dynamics of Mycobacterium tuberculosis in Northwest Ethiopia: new phylogenetic lineages found in Northwest Ethiopia

Belay Tessema1235*, Joerg Beer2, Matthias Merker4, Frank Emmrich35, Ulrich Sack35, Arne C Rodloff2 and Stefan Niemann4

Author Affiliations

1 Department of Medical Microbiology, College of Medicine and Health Sciences, University of Gondar, Gondar, Ethiopia

2 Institute of Medical Microbiology and Epidemiology of Infectious Diseases, University Hospital of Leipzig, Leipzig, Germany

3 Institute of Clinical Immunology, University Hospital of Leipzig, Leipzig, Germany

4 Molecular Mycobacteriology, Research Center Borstel, Borstel, Germany

5 Translational Centre for Regenerative Medicine, University of Leipzig, Leipzig, Germany

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BMC Infectious Diseases 2013, 13:131  doi:10.1186/1471-2334-13-131

Published: 11 March 2013

Abstract

Background

Although Ethiopia ranks seventh among the world’s 22 high-burden tuberculosis (TB) countries, little is known about strain diversity and transmission. In this study, we present the first in-depth analysis of the population structure and transmission dynamics of Mycobacterium tuberculosis strains from Northwest Ethiopia.

Methods

In the present study, 244 M. tuberculosis isolates where analysed by mycobacterial interspersed repetitive unit - variable number tandem repeat 24-loci typing and spoligotyping methods to determine phylogenetic lineages and perform cluster analysis. Clusters of strains with identical genotyping patterns were considered as an indicator for the recent transmission.

Results

Of 244 isolates, 59.0% were classified into nine previously described lineages: Dehli/CAS (38.9%), Haarlem (8.6%), Ural (3.3%), LAM (3.3%), TUR (2.0%), X-type (1.2%), S-type (0.8%), Beijing (0.4%) and Uganda II (0.4%). Interestingly, 31.6% of the strains were grouped into four new lineages and were named as Ethiopia_3 (13.1%), Ethiopia_1 (7.8%), Ethiopia_H37Rv like (7.0%) and Ethiopia_2 (3.7%) lineages. The remaining 9.4% of the isolates could not be assigned to the known or new lineages. Overall, 45.1% of the isolates were grouped in clusters, indicating a high rate of recent transmission.

Conclusions

This study confirms a highly diverse M. tuberculosis population structure, the presence of new phylogenetic lineages and a predominance of the Dehli/CAS lineage in Northwest Ethiopia. The high rate of recent transmission indicates defects of the TB control program in Northwest Ethiopia. This emphasizes the importance of strengthening laboratory diagnosis of TB, intensified case finding and treatment of TB patients to interrupt the chain of transmission.

Keywords:
Mycobacterium tuberculosis; Molecular epidemiology; Transmission dynamics