Bionomics and ecology of Anopheles merus along the East and Southern Africa coast

Abstract

Malaria transmission persists despite the scale-up of interventions such as long-lasting insecticide-treated nets (LLINs) and indoor residual spraying (IRS). Understanding the entomological drivers of transmission is key for the design of effective and sustainable tools to address the challenge. Recent research findings indicate a shift in vector populations from the notorious Anopheles gambiae (s.s.) as a dominant vector to other species as one of the factors contributing to the persistence of malaria transmission. However, there are gaps in the literature regarding the minor vector species which are increasingly taking a lead role in malaria transmission. Currently, minor malaria vectors have behavioural plasticity, which allows their evasion of vector control tools currently in use. To address this, we have reviewed the role of Anopheles merus, a saltwater mosquito species that is becoming an important vector of malaria transmission along the East and Southern African coast. We performed a literature review from PubMed and Google Scholar and reviewed over 50 publications relating to An. merus's bionomics, taxonomy, spatial-temporal distribution and role in malaria transmission. We found that An. merus is an important vector of malaria and that it contributes to residual malaria transmission because of its exophilic tendencies, insecticide resistance and densities that peak during the dry seasons as the freshwater mosquitoes decline. Spatial and temporal studies have also shown that this species has increased its geographical range, densities and vectorial capacity over time. In this review, we highlight the resting behaviour and breeding habitats of this mosquito, which could be targeted for surveillance studies and control interventions.

Keywords: Anopheles merus; Indoor residual spraying; Insecticide resistance; Plasmodium falciparum.

Fig. 1

Flow chart describing the database search and selection of the articles used in the literature review

Fig. 2

Map depicting sites where An. merus have been identified from mosquito collections along the East and Southern African Coast

Fig. 3

Proportions of An. gambiae complex members: An. gambiae (s.s.), An. merus, An. quadriannulatus and An. arabiensis in the different collection sites along the East and Southern African Coast. However, in Changombe, Drain Marie, Grand Baie, L’Isle’d’Ambre, Pemba and Pointe aux Piments, An. gambie (s.l.) were identified using a salt tolerance test and classified as saltwater An. gambiae represented as An. merus in the figure or non-saltwater An. gambiae (An. arabiensis, An. quadriannulatus, An. gambiae), which are represented as An. gambiae

Fig. 4

Species distribution and diversity indices of An. gambiae (s.l.) collections in sites along the East and Southern African Coast. Analysis was only done for sites where mosquitoes were identified through PCR or cytotaxonomy