Changing Plasmodium falciparum malaria prevalence in two villages of northeastern Tanzania between 2003 and 2021 in relation to vectors, interventions and climatic factors.

Abstract

Background: Malaria, which affects over half of the world's population, is controlled through clinical interventions and vector control strategies. However, these efforts are threatened by resistance to anti-malarial drugs and insecticides, as well as affected by environmental, ecological, and climatic changes. This study examined changes in malaria prevalence and related factors based on data from 18 cross-sectional surveys conducted in two villages in northeastern Tanzania.

Methods: From 2003 to 2021, annual cross-sectional malariometric surveys were conducted in two study villages, Mkokola (lowland) and Kwamasimba (highland), samples collected to determine Plasmodium falciparum infection and human exposure to malaria vector Anopheles. Pearson's chi-squared test was used for comparing proportions, logistic and linear regressions test were used analyse associations. Generalized Estimating Equations (GEE) was used to analyse the relationship between malaria prevalence and climatic variables.

Results: Malaria prevalence in Kwamasimba and Mkokola dropped from ~ 25% and ~ 80% to 0% and 1%, respectively, between 2003 and 2011, reaching 0% in both villages by 2014. This decline was associated with increased bed net use and reduced exposure to Anopheles bites. However, between 2018 and 2021, prevalence resurged, with Kwamasimba reaching 2003-2004 levels despite high bed net use. Between 2003 and 2021 there was an increasing trend in average monthly maximum temperatures (R2 = 0.1253 and 0.2005), and precipitation (R2 = 0.125 and 0.110) as well as minimum relative humidity (R2 = 0.141 and 0.1162) in Kwamasimba and Mkokola villages, respectively, while maximum relative humidity slightly decreased. Furthermore, during 2003-2011, malaria prevalence was positively associated with temperature, maximum temperature, and relative humidity, while precipitation showed a negative association (Estimate:- 0.0005, p < 0.001). Between 2012-2021, all climatic factors, including temperature (Estimate: 0.0256, p < 0.001), maximum temperature (Estimate: 0.0121, p < 0.001), relative humidity (Estimate: 0.00829, p < 0.001), and precipitation (Estimate: 0.000105, p < 0.001), showed positive associations.

Conclusion: From 2003 to 2014, malaria prevalence declined in two Tanzanian villages but resurged after 2018, particularly in highland Kwamasimba. Most likely, vector dynamics affected by changing climatic conditions drove this resurgence, emphasizing the need for adaptive, climate-informed malaria control strategies.