Multidisciplinary Investigations of Sustained Malaria Transmission in the Greater Mekong Subregion

Abstract

In the course of malaria elimination in the Greater Mekong Subregion (GMS), malaria epidemiology has experienced drastic spatiotemporal changes with residual transmission concentrated along international borders and the rising predominance of Plasmodium vivax. The emergence of Plasmodium falciparum parasites resistant to artemisinin and partner drugs renders artemisinin-based combination therapies less effective while the potential spread of multidrug-resistant parasites elicits concern. Vector behavioral changes and insecticide resistance have reduced the effectiveness of core vector control measures. In recognition of these problems, the Southeast Asian International Center of Excellence for Malaria Research (ICEMR) has been conducting multidisciplinary research to determine how human migration, antimalarial drug resistance, vector behavior, and insecticide resistance sustain malaria transmission at international borders. These efforts allow us to comprehensively understand the ecology of border malaria transmission and develop population genomics tools to identify and track parasite introduction. In addition to employing in vivo, in vitro, and molecular approaches to monitor the emergence and spread of drug-resistant parasites, we also use genomic and genetic methods to reveal novel mechanisms of antimalarial drug resistance of parasites. We also use omics and population genetics approaches to study insecticide resistance in malaria vectors and identify changes in mosquito community structure, vectorial potential, and seasonal dynamics. Collectively, the scientific findings from the ICEMR research activities offer a systematic view of the factors sustaining residual malaria transmission and identify potential solutions to these problems to accelerate malaria elimination in the GMS.

Figure 1.

Spatial distribution of malaria incidence in the border areas of Thailand, 2017–2021. The figure illustrates persistent border malaria despite the gradual reduction of annual malaria incidence. Neighboring countries and scale bar are marked in one panel. This figure appears in color at www.ajtmh.org.

Figure 2.

Dynamics of confirmed P. vivax and P. falciparum cases from passive case detection at the Laiza township hospital in Myanmar, 2017–2021. The Inset panel shows the dominance of P. vivax. The vivax malaria outbreak in 2016–2017 was effectively suppressed by vector-based control efforts (IRS and street fumigation). Case rebounds were noticed in 2020–2021, which may be due to reduced control efforts during COVID-19. This figure appears in color at www.ajtmh.org.

Figure 3.

Map of the GMS showing the prevalence and distribution of major PfK13 mutations as pie graphs above the malaria incidence heatmap of the region in 2020. The PfK13 mutation status was updated using malaria parasites collected primarily in 2016 from Cambodia, Laos, Vietnam, Thailand,^, and Myanmar.^,, This figure appears in color at www.ajtmh.org.