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Anopheles Gambiae Reemergence and Resurgent Malaria Transmission in Eastern Rwanda, 2010–2020: A Retrospective Observational Study
18 Pages Posted: 4 Oct 2023
More...Abstract
Background: Rwanda achieved unprecedented malaria control gains from 2000 to 2011, but cases increased 20-fold between 2011 and 2017. Vector control challenges and environmental changes were noted as potential explanations, but no studies have investigated causes of the resurgence or identified which vector species drove transmission.
Methods: We conducted a retrospective, longitudinal observational study in four sites in eastern Rwanda which performed monthly entomological surveillance and provided outpatient malaria care. We compared sporozoite rates, human blood index (HBI), and relative abundance of the primary vectors, Anopheles gambiae and An. arabiensis. We assessed the effects of vector control interventions, insecticide resistance, and temperature changes on species composition and reported malaria incidence from 2010 to 2020 using log-binomial and Poisson models.
Findings: Sporozoite rates were 28 times higher and HBI was four times higher in An. gambiae compared to An. arabiensis. An. gambiae was reduced following country-wide net distributions in 2010, but rapid increases in pyrethroid resistance were associated with increased An. gambiae relative abundance and malaria incidence. Epidemic malaria peaks corresponded to periods of An. gambiae reemergence. A 2.3°C increase in regional air temperatures during the period was associated with a 61% increase in malaria incidence. Non-pyrethroid indoor residual spraying was associated with reductions in An. gambiae sporozoite rates from 20% to 0%, relative abundance by 86%, and malaria incidence by 75%.
Interpretation: Pyrethroid resistance and regional warming were associated with the reemergence of An. gambiae and resurgent malaria transmission in eastern Rwanda. However, non-pyrethroid control measures appeared effective in mitigating vector reemergence and climate-related malaria increases.
Funding: Research reported in this publication was supported by the National Institute of Allergy and Infectious Diseases of the NIH under Award Number T32AI138952 and the Infectious Disease Across Scales Training Program (IDASTP) of Emory University.
Declaration of Interest: All authors state no conflicts of interest.
Ethical Approval: This study was reviewed by the Rwanda National Ethics Committee and the Emory University Institutional Review Board and was determined to be exempt from further review because it relied on de-identified, routinely collected surveillance data.
Keywords: Malaria, malaria resurgence, malaria epidemic, vector control, anopheles gambiae, insecticide resistance, climate and health
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