Abstract
The Nigerian Government is scaling up the distribution of insecticide-treated bed nets for malaria control, but the lack of surveillance data, especially in the Sudan/Sahel region of the country, may hinder targeting priority populations. Here, the vectorial role and insecticide resistance profile of a population of a major malaria vector Anopheles funestus sensu stricto from Sahel of Nigeria was characterised. An. funestus s.s. was the only vector found, with a high human blood index (100%) and a biting rate of 5.3/person/night. High Plasmodium falciparum infection was discovered (sporozoite rate = 54.55%). The population is resistant to permethrin (mortality = 48.30%, LT50 = 65.76 min), deltamethrin, DDT (dichlorodiphenyltrichloroethane) and bendiocarb, with mortalities of 29.44%, 56.34% and 54.05%, respectively. Cone-bioassays established loss of efficacy of the pyrethroid-only long-lasting insecticidal nets (LLINs); but 100% recovery of susceptibility was obtained for piperonylbutoxide (PBO)-containing PermaNet®3.0. Synergist bioassays with PBO and diethyl maleate recovered susceptibility, implicating CYP450s (permethrin mortality = 78.73%, χ2 = 22.33, P < 0.0001) and GSTs (DDT mortality = 81.44%, χ2 = 19.12, P < 0.0001). A high frequency of 119F GSTe2 mutation (0.84) was observed (OR = 16, χ2 = 3.40, P = 0.05), suggesting the preeminent role of metabolic resistance. These findings highlight challenges associated with deployment of LLINs and indoor residual spraying (IRS) in Nigeria.
Highlights
Nigeria tops the list of the countries with the highest burden of malaria, accounting for ~25% of all malaria cases worldwide and 19% of the 435,000 malaria-related deaths [1]
In stark contrast to An. gambiae s.l. [5,6,7], the major malaria vector An. funestus from the Sudan/Sahel savannah of northern Nigeria has been neglected for decades, after comprehensive works conducted by several pioneers, before 1960
This study discovered a disproportionately high Plasmodium infection in a major malaria vector
Summary
Nigeria tops the list of the countries with the highest burden of malaria, accounting for ~25% of all malaria cases worldwide and 19% of the 435,000 malaria-related deaths [1]. [5,6,7], the major malaria vector An. funestus from the Sudan/Sahel savannah of northern Nigeria has been neglected for decades, after comprehensive works conducted by several pioneers, before 1960. These almost seven decades old studies include (i) the work of Bruce-Chwatt and Haworth (carried out in 1955–56), which described An. funestus populations from Sokoto, north-western Nigeria, highly resistant to DDT (dichlorodiphenyltrichloroethane), dieldrin, and benzene hexachloride [8]; (ii) a detailed examination of An. funestus species, published in 1959 by W.M. Service [9] and its role in transmission in northern
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