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A survey of Anopheles species composition and insecticide resistance on the island of Bubaque, Bijagos Archipelago, Guinea-Bissau

Authors
  • Ant, Thomas1
  • Foley, Erin1
  • Tytheridge, Scott1
  • Johnston, Colin1
  • Goncalves, Adriana1
  • Ceesay, Sainey2
  • Ndiath, Mamadou Ousmane2
  • Affara, Muna2
  • Martinez, Julien1
  • Pretorius, Elizabeth1
  • Grundy, Chris3
  • Rodrigues, Amabelia4
  • Djata, Paulo5
  • d’Alessandro, Umberto6
  • Bailey, Robin1
  • Mabey, David1
  • Last, Anna1
  • Logan, James G.1, 7
  • 1 London School of Hygiene and Tropical Medicine, Keppel Street, London, WC1E 7HT, UK , London (United Kingdom)
  • 2 London School of Hygiene and Tropical Medicine, Fajara, The Gambia , Fajara (Gambia)
  • 3 Faculty of Epidemiology and Population Health, London School of Hygiene and Tropical Medicine, Keppel Street, London, WC1E 7HT, UK , London (United Kingdom)
  • 4 Bandim Health Project, INDEPTH Network, Bissau, Guinea-Bissau , Bissau (Guinea-Bissau)
  • 5 Ministério da saude chez Ministério da saude de Guinea-Bissau, Bissau, Guinea-Bissau , Bissau (Guinea-Bissau)
  • 6 MRC The Gambia at the London School of Hygiene & Tropical Medicine, Fajara, Gambia , Fajara (Gambia)
  • 7 ARCTEC, Chariot Innovations Ltd, London School of Hygiene and Tropical Medicine, Keppel Street, London, WC1E 7HT, UK , London (United Kingdom)
Type
Published Article
Journal
Malaria Journal
Publisher
Springer (Biomed Central Ltd.)
Publication Date
Jan 15, 2020
Volume
19
Issue
1
Identifiers
DOI: 10.1186/s12936-020-3115-1
Source
Springer Nature
Keywords
License
Green

Abstract

BackgroundBubaque is the most populous island of the Bijagos archipelago, a group of malaria-endemic islands situated off the coast of Guinea-Bissau, West Africa. Malaria vector control on Bubaque relies almost exclusively on the use of long-lasting insecticidal nets (LLINs). However, there is little information on local vector bionomics and insecticide resistance.MethodsA survey of mosquito species composition was performed at the onset of the wet season (June/July) and the beginning of the dry season (November/December). Sampling was performed using indoor adult light-traps and larval dipping. Anopheles mosquitoes were identified to species level and assessed for kdr allele frequency by TaqMan PCR. Females were analysed for sporozoite positivity by CSP-ELISA. Resistance to permethrin and α-cypermethrin was measured using the CDC-bottle bioassay incorporating the synergist piperonyl-butoxide.ResultsSeveral Anopheles species were found on the island, all belonging to the Anopheles gambiae sensu lato (s.l.) complex, including An. gambiae sensu stricto, Anopheles coluzzii, Anopheles melas, and An. gambiae/An. coluzzii hybrids. Endophagic Anopheles species composition and abundance showed strong seasonal variation, with a majority of An. gambiae (50% of adults collected) caught in June/July, while An. melas was dominant in November/December (83.9% of adults collected). Anopheles gambiae had the highest sporozoite rate in both seasons, with infection rates of 13.9% and 20% in June/July and November/December, respectively. Moderate frequencies of the West African kdr allele were found in An. gambiae (36%), An. coluzzii (35%), An. gambiae/An. coluzzii hybrids (42%). Bioassays suggest moderate resistance to α-cypermethrin, but full susceptibility to permethrin.ConclusionsThe island of Bubaque maintained an An. gambiae s.l. population in both June/July and November/December. Anopheles gambiae was the primary vector at the onset of the wet season, while An. melas is likely to be responsible for most dry season transmission. There was moderate kdr allele frequency and synergist assays suggest likely metabolic resistance, which could reduce the efficacy of LLINs. Future control of malaria on the islands should consider the seasonal shift in mosquito species, and should employ continuous monitoring for insecticide resistance.

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