Molecular epidemiology of tuberculosis in northeastern Ethiopia

Abstract

Background: Tuberculosis (TB) is a major public health threat causing the highest morbidity and mortality in Ethiopia. However, there is shortage of information on the species and strains of mycobacteria that cause TB in Ethiopia. The objective of this study is to investigate the diversity of Mycobacterium tuberculosis (M. tb) isolated from TB patients in northeastern Ethiopia. Methods: A total of 384 smear positive pulmonary and extra-pulmonary TB cases were recruited on the basis of clinical examination and ZiehlNeelsen staining for further investigation. Mycobacterial culturing, region of difference (RD) 9-based polymerase chain reaction (PCR), spoligotyping and mycobacterial interspersed repetitive unit-variable-number tandem repeat (MIRU-VNTR) typing were used for the identification the species and strains. Descriptive statistical analysis was used for the expression of the results while proportions were compared using c2 test. Statistical significance was considered when p<0.05.Results: Smear positive pulmonary tuberculosis accounted for 74.5% (286/384). The disease proportion was highest in age group of 18–37 years. Culture positivity was confirmed only in 29.2% (112/384). Speciation of the culture positive isolates using RD9 indicated that 77.7% (87/112) were M. tuberculosis. Further identification of the isolates using spoligotyping indicated 92.9% (104/112) interpretable spoligotyping patterns of which 20.2% (21/104) were grouped under 10 clustered patterns. Further grouping of the spoligotypes indicated that 86.5% (90/104) of the isolates as orphan types. Grouping of the isolates into the major lineages showed 52.9%, 27.9% and 19.2% of the isolates as Euroamerican, Indio-oceanic and East African Indian lineages, respectively. Typing of 69 isolates using 24-loci MIRU-VNTR typing gave interpretable results for 56 isolates each of them having distinct MIRU-VNTR profile and were considered as 56 different genotypes (strains).Conclusion: M. tuberculosis was identified as the main cause of TB in northeastern Ethiopia and its strains were highly diversified.