Variation in Anopheles distribution and predictors of malaria infection risk across regions of Madagascar

Abstract

Background: Deforestation and land use change is widespread in Madagascar, altering local ecosystems and creating opportunities for disease vectors, such as the Anopheles mosquito, to proliferate and more easily reach vulnerable, rural populations. Knowledge of risk factors associated with malaria infections is growing globally, but these associations remain understudied across Madagascar's diverse ecosystems experiencing rapid environmental change. This study aims to uncover socioeconomic, demographic, and ecological risk factors for malaria infection across regions through analysis of a large, cross-sectional dataset.

Methods: The objectives were to assess (1) the ecological correlates of malaria vector breeding through larval surveys, and (2) the socioeconomic, demographic, and ecological risk factors for malaria infection in four ecologically distinct regions of rural Madagascar. Risk factors were determined using multilevel models for the four regions included in the study.

Results: The presence of aquatic agriculture (both within and surrounding communities) is the strongest predictive factor of habitats containing Anopheles larvae across all regions. Ecological and socioeconomic risk factors for malaria infection vary dramatically across study regions and range in their complexity.

Conclusions: Risk factors for malaria transmission differ dramatically across regions of Madagascar. These results may help stratifying current malaria control efforts in Madagascar beyond the scope of existing interventions.

Keywords: Disease ecology; Land use change; Malaria; Planetary health; Vector-borne disease.

Fig. 1

Heatmap of individual, household, and site-level predictors of the outcome: the proportion of the population with malaria (RDT +) by site. Darker colors signify higher percentiles, lighter colors signify lower percentiles. Satellite imagery obtained from SPOT6 and SPOT7 satellites. Site marker color corresponds to malaria prevalence in each site

Fig. 2

Larval mosquito species information. a: Larval habitats found near households in rural Madagascar, separated by region and habitat type. Dark grey boxes indicate habitats with Anopheles, while light grey boxes indicate habitats with other genera of mosquitoes. Anopheles species abundance in each region is displayed in the bar charts below. b Distribution of the amount of aquatic agriculture surrounding households (within a 500-m radius) with 0 (grey), 1 + (light blue), or 2 + (dark blue) malaria infections. The HP region was not included due to too few individuals with malaria

Fig. 3

a The observed difference in malaria prevalence between groups. Variables are at the site or regional levels, such that bars represent the regional average or the site average depending on how they were coded for the models. Bars > 0% demonstrate increased risk, bars < 0% demonstrate decreased risk. Colours correspond to their respective Venn diagram colors in (b). b Venn diagram demonstrating statistically significant predictors for increased malaria risk in the multilevel models employed for each region