Spatio-Temporal Distribution of Mycobacterium tuberculosis Complex Strains in Ghana

Abstract

BackgroundThere is a perception that genomic differences in the species/lineages of the nine species making the Mycobacterium tuberculosis complex (MTBC) may affect the efficacy of distinct control tools in certain geographical areas. We therefore analyzed the prevalence and spatial distribution of MTBC species and lineages among isolates from pulmonary TB cases over an 8-year period, 2007–2014.MethodologyMycobacterial species isolated by culture from consecutively recruited pulmonary tuberculosis patients presenting at selected district/sub-district health facilities were confirmed as MTBC by IS6110 and rpoß PCR and further assigned lineages and sub lineages by spoligotyping and large sequence polymorphism PCR (RDs 4, 9, 12, 702, 711) assays. Patient characteristics, residency, and risks were obtained with a structured questionnaire. We used SaTScan and ArcMap analyses to identify significantly clustered MTBC lineages within selected districts and spatial display, respectively.ResultsAmong 2,551 isolates, 2,019 (79.1%), 516 (20.2%) and 16 (0.6%) were identified as M. tuberculosis sensu stricto (MTBss), M. africanum (Maf), 15 M. bovis and 1 M. caprae, respectively. The proportions of MTBss and Maf were fairly constant within the study period. Maf spoligotypes were dominated by Spoligotype International Type (SIT) 331 (25.42%), SIT 326 (15.25%) and SIT 181 (14.12%). We found M. bovis to be significantly higher in Northern Ghana (1.9% of 212) than Southern Ghana (0.5% of 2339) (p = 0.020). Using the purely spatial and space-time analysis, seven significant MTBC lineage clusters (p< 0.05) were identified. Notable among the clusters were Ghana and Cameroon sub-lineages found to be associated with north and south, respectively.ConclusionThis study demonstrated that overall, 79.1% of TB in Ghana is caused by MTBss and 20% by M. africanum. Unlike some West African Countries, we did not observe a decline of Maf prevalence in Ghana.

Reduced transmission ofMycobacterium africanumcompared toM. tuberculosisin urban West Africa

“…The higher recent transmission rate for L4 compared to L5 may arguably just be a mirage and may not necessarily imply the outcompeting of L5 by L4 as their relative proportions still remain constant over the entire study period of this current study (Figure 3) and also from previous reports. 16 The reduced prevalence and transmission of L5 may just be a result of a bottleneck event which might have taken place in the past resulting in the reduction of Maf population at the time and ever since. Maf has been transmitting at this same average rate ensuring a stable population proportion over time.…”

“…11,14,15 However, an 8-year study recently conducted in Ghana found the prevalence of Maf to be fairly constant with approximately 20% indicating that Maf may transmit as equally as MTBss (mainly L4). 16 The objective of the study was to determine the transmission dynamics of TB caused by MTBss and Maf.…”

Phylogenetic population structure and drug resistance of Mycobacterium tuberculosis complex in the Volta Region of Ghana

“…(5). However, findings from recent studies still indicate significant presence of Maf within West Africa (6)(7)(8). One reason for the high prevalence of Maf might be due to the stable adaptation of this lineage to some human populations.…”

Comparative genomics ofMycobacterium africanumLineage 5 and Lineage 6 from Ghana suggests different ecological niches

“…Even though the report of a steady decline of Maf associated TB in some settings seems to support the first hypothesis 19–21 , other studies indicate that Maf remains an important cause of TB in West-Africa 22–24 . In Ghana for instance, a recent study showed that the proportion of TB due to Maf remained constant over the 8 year study period 25 . Even though, the reported statistical association of L5 with ethnicity in Ghana suggests a possible co-evolutionary scenario in favour of the second hypothesis, genetic evidence of co-evolution/co-adaptation remains to be demonstrated.…”