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. 2025 Jun 19;24(1):195.
doi: 10.1186/s12936-025-05372-z.

A survey of indoor and outdoor Anopheles density, species composition and circumsporozoite rate of malaria vectors on the Bijagós Archipelago, Guinea-Bissau

Elizabeth Pretorius  1 , Robert T Jones  2   3 , Harry Hutchins  4 , Eunice Teixeira Da Silva  5   6 , Sainey Ceesay  7 , Mamadou Ousmane Ndiath  7 , Umberto d'Alessandro  7 , Amabelia Rodrigues  5   6 , James G Logan  8   9 , Anna Last  4
Affiliations

A survey of indoor and outdoor Anopheles density, species composition and circumsporozoite rate of malaria vectors on the Bijagós Archipelago, Guinea-Bissau

Elizabeth Pretorius et al. Malar J. .

Abstract

Background: The malaria-endemic Bijagós Archipelago is situated 50 km off the coast of mainland Guinea-Bissau. It is a seasonal malaria transmission setting, with insecticide-treated bed nets as its primary control strategy. Little is known about the vector diversity and behaviour across the Archipelago.

Methods: In 2019, a survey took place on 16 of the inhabited islands across the Archipelago. Adult mosquitoes were collected using odour-baited outdoor light traps and indoor light traps at houses selected at random. Larval surveys were conducted for each village sampled. Anopheles adults caught were morphologically identified and a sub-sample was analysed to identify species within the Anopheles gambiae complex using RFLP-PCR. Sporozoite positivity was detected within a sub-sample by CSP-ELISA.

Results: Anopheles gambiae sensu lato was present on all islands sampled. Anopheles density varied between islands, with densities ranging from 0.0 to 98.7 per trapping night from indoor traps and 0.1-165.2 per trapping night from outdoor traps. Anopheles melas was the most commonly observed species, accounting for 85.2% of all Anopheles caught from both indoor and outdoor light traps. A high level of hybridization between An. gambiae sensu stricto and Anopheles coluzzii was seen on some islands across the Archipelago. The overall sporozoite rate was 0.86% (0.2% for indoor traps; 1.4% for outdoor traps).

Conclusions: Species within An. gambiae s.l. are the primary vectors on the Bijagós. Anopheles melas may contribute to transmission throughout the year in the Bijagós. The vector species composition, abundance and infection rates uncovered in this study are useful for informing tailored, effective vector control programme in the Bijagos.

Keywords: Anopheles gambiae; Bijagós Archipelago; Guinea-Bissau; Malaria; Vector survey.

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Conflict of interest statement

Declarations. Ethics approval and consent to participate.: The work presented was discussed and approved by ethics committees at the London School of Hygiene and Tropical Medicine (Ref No. 14431) and locally in Guinea-Bissau (Comité de Éticas na Saúde) Ref No. 076/CNES/INASA/2017. Consent for publication: Not applicable. Competing interests: The authors declare no competing interests.

Figures

Fig. 1
Fig. 1
Map of the Bijagós Archipelago showing villages and Anopheles larval sites sampled in 2019. Location of the Archipelago in West Africa shown in inset
Fig. 2
Fig. 2
Anopheles density (number per trapping night) from indoor (red) and outdoor (blue) LTs across the Bijagós Archipelago
See this image and copyright information in PMC

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