Distinct TB strains and local spread found in rural northwest Ethiopia

Tuberculosis remains caused by many different strains of Mycobacterium tuberculosis (Mtb), and those strains can vary a lot from place to place. That variation matters for tracking the disease and tailoring control efforts, so researchers led by Kelemework Adane set out to map which Mtb types are present in a largely rural part of Ethiopia. The team collected samples from patients at two public hospitals serving East Gojjam, in the Amhara Region of northwest Ethiopia, and used molecular tools to identify the bacteria. Their goal was to see which lineages and sublineages of Mtb are circulating in this community, because earlier work has shown that Ethiopia hosts a complex mix of strains. By focusing on predominantly rural patients and hospital-collected sputum samples, the researchers aimed to fill a geographic gap in knowledge about Mtb diversity. The study highlights why local surveys are important: different places can show very different patterns of Mtb lineages, and those patterns can affect how the disease spreads and how control measures should be targeted.

For laboratory work the study used region of difference 9 (RD9)-based polymerase chain reaction (PCR) and spoligotyping on stored sputum samples at Armauer Hansen Research Institute (AHRI) in Addis Ababa. From 120 Mtb isolates, 116 yielded interpretable spoligotyping results. Those results revealed four major lineages: Euro-American (Lineage 4) was the most common at 42.6%, followed by Ethiopian (Lineage 7) at 20.8%, Indo-Oceanic (Lineage 1) at 20.0%, and East African-Indian (Lineage 3) at 16.5%. The dominant sublineages were ETH1 (Lineage 7, 20.8%), T (Lineage 4, 15.6%), and CAS1-Delhi (Lineage 3, 13.9%). In total the team identified 39 spoligotype patterns, including 19 shared types (48.7%) that matched 90 strains in the SITVIT2 database. The most frequent spoligotypes were SIT 910 (23.3%) and SIT 53 (14.4%), with SIT 54 and SIT 149 each at 10.0%. Overall, 82.7% of the strains were clustered, indicating many infections were closely related.

These findings point to substantial genetic diversity of Mtb in a rural Ethiopian setting and highlight two notable features: a high prevalence of Ethiopian (Lineage 7) and Indo-Oceanic (Lineage 1) strains, and a strong signal of recent or ongoing local transmission. The high clustering rate (82.7%) suggests that many cases are part of local transmission chains rather than isolated, distant introductions. The study specifically notes transmission activity involving the ETH1, CAS1-Delhi, and Manu2 sublineages, which are prominent in the sample set. Because the strain mix in East Gojjam differs from other places, the authors conclude that more detailed work using whole-genome sequencing is essential. Whole-genome sequencing would provide finer resolution on how strains are related, how they move through communities, and which sublineages are driving local spread—information that can guide targeted TB control strategies and public health decisions in the region.