2La Paracentric Chromosomal Inversion and Overexpressed Metabolic Genes Enhance Thermotolerance and Pyrethroid Resistance in the Major Malaria Vector Anopheles gambiae

Abstract

Changes in global temperature are impacting the spread/intensity of vector-borne diseases, including malaria, and accelerating evolutionary/adaptive changes in vector species. These changes, including chromosomal inversions and overexpression and/or changes in allele frequencies of thermotolerance-associated genes, may facilitate insecticide resistance through pleiotropy. This study investigated the impact of thermotolerance on pyrethroid resistance in four populations of the malaria vector An. gambiae s.l., from the savanna/sub-Sahel of northern Nigeria. Anopheles coluzzii and An. gambiae s.s. were the only malaria vectors found, sympatric in all the sites, with the former species predominant. High thermotolerance was observed, with no mortality at 38 °C, and LT50 of ~44 °C. Significantly high permethrin resistance was observed (mortality < 50%) in 44 °C heat-hardened (exposure to an intermediately high temperature provides protection to a more severe temperature or insecticide) larvae from two sites, BUK and Pantami, compared with the control, and heat-hardened adult females from Auyo (mortality = 3.00% ± 1.20, χ2 = 5.83, p < 0.01) compared with the control (12.00% ± 4.65). The 2La chromosomal inversion was detected at ~50% in subset of larvae and 58% in subset of adult females genotyped. A significant association was observed (OR = 7.2, p < 0.03) between permethrin resistance and the 2La/+a rearrangement compared with 2L+a/+a, in BUK larvae. For all sites, permethrin resistance correlated with 2La/a homozygosity in adult females (R = 5.02, p = 0.01). qRT-PCR identified six genes commonly induced/overexpressed, including the heat shock protein 70 (AGAP004581) which was 2468× and 5× overexpressed in heat-hardened and permethrin-resistant females, respectively; trehalose-6-phosphate synthase (AGAP008227); and the ionotropic glutamate receptor genes, IR25a (AGAP010272) and IR21a (AGAP008511). This study highlights challenges associated with insecticide-based malaria vector control, and the epidemiological significance of taking climate variables into account for the design/choice of control measures.

Molecular drivers of insecticide resistance in the Sahelo-Sudanian populations of a major malaria vectorAnopheles coluzzii

“…gambiae (Greppi et al, 2020), with both shown to be overexpressed/induced in thermotolerant/permethrin resistant populations of An. coluzzii (Ibrahim et al, 2021).…”

“…These two genes were among the overexpressed genes in both heat-hardened and permethrin-resistant An. coluzzii populations from northern Nigeria (Ibrahim et al, 2021). Several ionotropic glutamate receptors were found within the 2La inversion breakpoints: IR136 (AGAP006440), IR139 (AGAP006691) and IR142 (AGAP006407).…”

“…gambiae is the dominant species in humid forest zones (Lindsay, 1998, Coetzee, 2000, Ranson et al, 2009, An. coluzzii has repeatedly been identified as the major malaria vector in the Sudan savannah and Sahel of several, neighbouring countries (including in northern Nigeria, southern Niger, central Chad, and northern Cameroon) (Ibrahim et al, 2019a, Ibrahim et al, 2019b, Ibrahim et al, 2019c, Fadel et al, 2019, Ibrahim et al, 2021 in recent years, suggesting that this vector has adapted well in drier regions of the Sahel transects, and is probably predominating over An. arabiensis and An.…”

“…Susceptibility to clothianidin was very high (Figure 6d), but surprisingly the CYP6Z2 transgenic flies exhibited a contrasting phenotype, with significantly higher mortalities of several, neighbouring countries (including in northern Nigeria, southern Niger, central Chad, and northern Cameroon) (7,(26)(27)(28)56) in recent years, suggesting that this vector has adapted well in drier regions of the Sahel transects, and is probably predominating over An.…”

“…It was also shown that inversion 2La assorts with insecticide resistance, e.g., dieldrin plus fipronil (Brooke et al, 2000), and is associated with thermotolerance and permethrin resistance in the Sahelain An. coluzzii (Ibrahim et al, 2021).…”