Ecological intelligence-gathering for malaria control

: Characterising the Anopheles larval community of Barotseland, western Zambia

Crynodeb

Human inhabitants of the Barotse floodplain traditionally migrate with their livestock to higher ground in response to seasonal flooding of the Zambezi river. This ecosystem offers a shifting mosaic of potential larval habitat and blood sources to malaria vector mosquitoes, and despite increased coverage of insecticide-treated nets and indoor residual spraying over several decades, residual malaria transmission is stubbornly high. This study aimed to characterise the region’s anopheline community by examining its species composition, exploring its spatiotemporal response to such dynamic ecohydrological conditions, and investigating whether environmental characteristics of habitats can explain individual species’ distributions.

Geographically extensive larval surveys covering > 110 km of transects yielded larval specimens subsequently identified using mitochondrial and nuclear DNA barcode sequencing, revealing a diverse assemblage of Anopheles species unexpectedly dominated by species considered of secondary importance in African malaria transmission. An. coustani, An. pharoensis and An. squamosus composed the majority of candidate vector larvae across dry (2017) and wet (2018, 2019) seasons, despite significant inter-annual variability between consecutive wet seasons, and primary vector species (An. arabiensis, An. gambiae and An. funestus) constituted < 2 % of sampled anophelines.

Implications for vector control efforts in the region are potentially significant, as crepuscular feeding and exploitation of non-human bloodmeals typically allows these secondary species to evade the influence of conventional indoor-focused interventions. Larval source management (LSM) techniques are increasingly advocated in this scenario, and zero-inflated generalised linear mixed modelling successfully explained 40-60 % of variance in the distributions of An. squamosus and An. pharoensis using rapidly-assessed ecological characteristics which could be assessed at operational scale. However, the approach was unable to capture the ubiquitous distribution of the predominant An. coustani larvae, posing a significant challenge to the feasibility of habitat targeting within LSM in a floodplain ecosystem too vast for blanket larviciding to be cost-effective.

Dyddiad Dyfarnu	2025
Iaith wreiddiol	Saesneg
Sefydliad Dyfarnu	Prifysgol Aberystwyth
Goruchwyliwr	Paul Shaw (Goruchwylydd)