Rwanda’s dominant drug-resistant TB strain found across Great Lakes borders

Tuberculosis that resists standard treatment remains a major public health challenge, and in Rwanda researchers had already spotted a worrying pattern: a single multidrug-resistant tuberculosis (MDR-TB) strain, named the R3clone, was behind roughly 70% of rifampicin-resistant TB cases in the country. To understand how far this successful clone reached, a team led by Conor J. Meehan turned to genetic surveillance. They first used whole-genome sequencing on MDR-TB isolates collected in Rwanda to define unique genetic signatures that set the R3clone apart from other Mycobacterium tuberculosis complex bacteria. With those defining features in hand, the team developed a targeted qPCR test that looks for a clone-specific single-nucleotide polymorphism. The approach was designed to be practical: pair broad genomic analysis to discover specific markers, then build a focused molecular test that can rapidly screen many samples. This combination aimed to show not just that the R3clone existed in Rwanda, but whether it had moved across borders into neighboring countries and beyond, information that is essential for tracking and controlling the spread of drug-resistant TB.

The researchers applied their two-part strategy—whole-genome sequencing to define the R3clone signature, followed by a targeted qPCR assay—to large collections of isolates. Using these tools, they screened isolates from Rwanda, neighboring countries, and public genomic repositories. In total they identified 375 R3clone isolates: 264 from historical Rwandan collections spanning 1991-2021, 49 from recent Rwandan diagnostic routine samples collected during 2021-2024, 25 from historical Burundi isolates collected between 2002-2013, and 37 from public repositories representing several countries. The R3clone-specific qPCR assay showed 100% specificity in distinguishing the R3clone from other MTBC (sub-)lineages, meaning it reliably told the R3clone apart from other strains. Transmission analysis based on the genetic data revealed cross-border movement of the R3clone within the Great Lakes Region, demonstrating that the dominant Rwandan MDR-TB clone is not confined to one country but has been transmitted across neighboring borders.

These findings carry clear implications for how health authorities monitor and respond to drug-resistant TB. The study shows that combining whole-genome sequencing to pinpoint unique signatures with a targeted qPCR test can both map and rapidly detect a dominant MDR-TB clone. Because the R3clone accounts for a large share of rifampicin-resistant TB in Rwanda and has been found in neighboring countries, the work underlines the need for coordinated, cross-border surveillance across the Great Lakes Region. Timely identification of such clones can inform public health responses, from case finding to treatment strategies, and helps countries track whether control efforts are working. The authors conclude that national programs should not work in isolation: molecular diagnostics and genomic surveillance need to be shared and aligned internationally to prevent further spread of dominant drug-resistant strains like the R3clone.