Geographically extensive larval surveys reveal an unexpected scarcity of primary vector mosquitoes in a region of persistent malaria transmission in western Zambia

Parasites & Vectors

Andy J. Hardy¹  Dónall Eoin Cross²  Niall McKeown²  Paul W. Shaw³  Vincent Siaziyu⁴  Chris Thomas⁵  Amy Healey⁵  Mark Macklin⁵  Andrew Silumesii⁶  Francis Liywalii⁷  Jacob Sakala⁷  Douglas Singini⁸  Mark Smith⁹  Tom Willis⁹ 

[1] Department of Geography and Earth Sciences, Aberystwyth University, SY23 3DB, Aberystwyth, UK;Institute of Biological, Environmental and Rural Sciences, Aberystwyth University, SY23 3FG, Aberystwyth, UK;Institute of Biological, Environmental and Rural Sciences, Aberystwyth University, SY23 3FG, Aberystwyth, UK;Department of Ichthyology and Fisheries Science, Rhodes University, Grahamstown, South Africa;Limulunga District Health Office, P.O. Box 910022, Mongu, Zambia;Lincoln Centre for Water and Planetary Health, School of Geography, College of Science, Think Tank, University of Lincoln, Ruston Way, LN6 7DW, Lincoln, UK;Ministry of Health, P.O. Box 30205, Lusaka, Zambia;Provincial Health Office, P.O. Box 910022, Western Province, Mongu, Zambia;Provincial Health Office, P.O. Box 910022, Western Province, Mongu, Zambia;School of Public Health and Health Systems, University of Waterloo, N2L 3G1, Waterloo, ON, Canada;School of Geography, University of Leeds, LS2 9JT, Leeds, UK;

关键词: Primary vector;    Secondary vector;    Anopheles;    Exophagy;    Malaria;    Residual transmission;    Larvae;    COI;    ITS2;   

DOI  :  10.1186/s13071-020-04540-1

来源: Springer

【 摘 要 】

BackgroundThe Barotse floodplains of the upper Zambezi River and its tributaries are a highly dynamic environment, with seasonal flooding and transhumance presenting a shifting mosaic of potential larval habitat and human and livestock blood meals for malaria vector mosquitoes. However, limited entomological surveillance has been undertaken to characterize the vector community in these floodplains and their environs. Such information is necessary as, despite substantial deployment of insecticide-treated nets (ITNs) and indoor residual spraying (IRS) against Anopheles vectors, malaria transmission persists across Barotseland in Zambia’s Western Province.MethodsGeographically extensive larval surveys were undertaken in two health districts along 102 km of transects, at fine spatial resolution, during a dry season and following the peak of the successive wet season. Larvae were sampled within typical Anopheles flight range of human settlements and identified through genetic sequencing of cytochrome c oxidase I and internal transcribed spacer two regions of mitochondrial and nuclear DNA. This facilitated detailed comparison of taxon-specific abundance patterns between ecological zones differentiated by hydrological controls.ResultsAn unexpected paucity of primary vectors was revealed, with An. gambiae s.l. and An. funestus representing < 2% of 995 sequenced anophelines. Potential secondary vectors predominated in the vector community, primarily An. coustani group species and An. squamosus. While the distribution of An. gambiae s.l. in the study area was highly clustered, secondary vector species were ubiquitous across the landscape in both dry and wet seasons, with some taxon-specific relationships between abundance and ecological zones by season.ConclusionsThe diversity of candidate vector species and their high relative abundance observed across diverse hydro-ecosystems indicate a highly adaptable transmission system, resilient to environmental variation and, potentially, interventions that target only part of the vector community. Larval survey results imply that residual transmission of malaria in Barotseland is being mediated predominantly by secondary vector species, whose known tendencies for crepuscular and outdoor biting renders them largely insensitive to prevalent vector control methods.

【 授权许可】

CC BY