Drug-Resistant RDRio Tuberculosis Strain Tracked Across Ecuador

Researchers in Ecuador have updated the molecular picture of the RDRio genotype of Mycobacterium tuberculosis, the bacterium that causes tuberculosis, and found that although the strain remains comparatively rare in the country, it carries a substantial burden of drug resistance. The study screened 699 clinical MTB isolates collected in 2018 and 2023 and identified 40 isolates, or 5.72 percent, as belonging to the RDRio genotype.

RDRio is a major genotype within the Latin American-Mediterranean, or LAM, family of MTB and has previously been associated with increased transmissibility and multidrug resistance, known as MDR. An earlier baseline study in Ecuador had reported a low prevalence of 2.09 percent for the period 2012 to 2016, and RDRio is highly endemic in Venezuela. The new figures therefore represent a nearly three-fold increase relative to that earlier baseline, although the authors note the prevalence remained stable across the 2018 to 2023 study window and low compared with high-endemicity settings such as Venezuela.

The surveillance effort was led by researchers at Universidad de Las Americas in Quito together with colleagues from institutions including Universidad Catolica de Santiago de Guayaquil, Universidad ECOTEC, the Instituto Nacional de Investigacion en Salud Publica, and the Universidad de Extremadura in Spain. The team screened isolates from two collection years, 384 isolates from 2018 and 315 from 2023, using duplex PCR to detect the RDRio genotype. Prevalence showed no significant difference between the two years, with 20 isolates, or 5.21 percent, positive in 2018 and 20 isolates, or 6.35 percent, positive in 2023.

Positive isolates were then characterized using a combination of classical and genomic typing methods: 24-locus MIRU-VNTR typing, spoligotyping, and whole-genome sequencing. Whole-genome sequencing confirmed that the dominant RDRio sublineages in Ecuador were 4.3.4.1 and 4.3.4.2, all of which fall within Lineage 4, the Euro-American lineage of MTB.

Genotypic resistance profiling of the sequenced isolates revealed a concerning pattern. Among the 28 isolates that were sequenced, 32.1 percent, or 9 of 28, were classified as multidrug-resistant tuberculosis, and a further 7.1 percent, or 2 of 28, were classified as pre-extensively drug-resistant, or pre-XDR, tuberculosis.

To assess how the Ecuadorian strains relate to one another and to strains from elsewhere, the researchers constructed minimum spanning trees based on MIRU-VNTR profiles, a standard approach for estimating genetic relatedness among bacterial isolates. The analysis showed that RDRio isolates from Ecuador segregated predominantly into distinct clonal complexes, meaning that the circulating strains formed their own genetically coherent groups rather than mixing broadly with outside strains.

Notably, the Ecuadorian RDRio isolates remained largely isolated from international reference strains, including isolates from Venezuela. The authors state that this genetic segregation of the predominant Ecuadorian RDRio clonal complex from international reference strains, Venezuelan isolates included, did not support recent importation associated with the Venezuelan diaspora. In other words, despite the timing of large migration flows from a country where the genotype is highly endemic, the genetic data did not point to recent introduction of RDRio strains through that route.

The study, published as a Brief Research Report in Frontiers in Public Health in the section on Infectious Diseases: Epidemiology and Prevention, received on 16 August 2026 and accepted on 16 October 2026, positions its findings as an update to the molecular epidemiology of RDRio in Ecuador.

Despite the relatively low prevalence of the genotype overall, the authors emphasize that RDRio was associated with a substantial burden of drug resistance among the isolates they characterized.

Subject of Research: Molecular epidemiology and drug resistance of the RDRio genotype of Mycobacterium tuberculosis in Ecuador

Article Title: Molecular epidemiology of the RDRio genotype of Mycobacterium tuberculosis in Ecuador: a tracking update for the years 2018 and 2023

Article References: Rodríguez-Pazmiño, Á. S., Cedeño-Vásquez, M. P., Pozo-Estupiñán, L. P., Trejo Cedeño, I., Cárdenas Franco, G., Salcedo Maldonado, A. B., Orlando, S. A., Franco-Sotomayor, G., Jimenez-Pizarro, N., Hermoso de Mendoza, J., & Garcia-Bereguiain, M. A. (2026). Molecular epidemiology of the RDRio genotype of Mycobacterium tuberculosis in Ecuador: a tracking update for the years 2018 and 2023. Frontiers in Public Health, 14, 1969751. https://doi.org/10.3389/fpubh.2026.1969751

Image Credits: AI Generated

DOI: 10.3389/fpubh.2026.1969751

Keywords: tuberculosis, Mycobacterium tuberculosis, RDRio genotype, Ecuador, drug resistance, MDR-TB, molecular epidemiology, MIRU-VNTR, whole-genome sequencing, public health, Molecular, epidemiology