Kenya Medical Research Institute, Centre for Geographic Medicine Research-Coast, Kilifi, Kenya.
Pwani University Bioscience Research Centre (PUBReC), Pwani University, Kilifi, Kenya.
Parasit Vectors. 2022 Dec 1;15(1):448. doi: 10.1186/s13071-022-05491-5.
Malaria remains one of the most important infectious diseases in sub-Saharan Africa, responsible for approximately 228 million cases and 602,000 deaths in 2020. In this region, malaria transmission is driven mainly by mosquitoes of the Anopheles gambiae and, more recently, Anopheles funestus complex. The gains made in malaria control are threatened by insecticide resistance and behavioural plasticity among these vectors. This, therefore, calls for the development of alternative approaches such as malaria transmission-blocking vaccines or gene drive systems. The thioester-containing protein 1 (TEP1) gene, which mediates the killing of Plasmodium falciparum in the mosquito midgut, has recently been identified as a promising target for gene drive systems. Here we investigated the frequency and distribution of TEP1 alleles in wild-caught malaria vectors on the Kenyan coast.
Mosquitoes were collected using CDC light traps both indoors and outdoors from 20 houses in Garithe village, along the Kenyan coast. The mosquitoes were dissected, and the different parts were used to determine their species, blood meal source, and sporozoite status. The data were analysed and visualised using the R (v 4.0.1) and STATA (v 17.0).
A total of 18,802 mosquitoes were collected, consisting of 77.8% (n = 14,631) Culex spp., 21.4% (n = 4026) An. gambiae sensu lato, 0.4% (n = 67) An. funestus, and 0.4% (n = 78) other Anopheles (An. coustani, An. pharoensis, and An. pretoriensis). Mosquitoes collected were predominantly exophilic, with the outdoor catches being higher across all the species: Culex spp. 93% (IRR = 11.6, 95% Cl [5.9-22.9] P < 0.001), An. gambiae s.l. 92% (IRR = 7.2, 95% Cl [3.6-14.5]; P < 0.001), An. funestus 91% (IRR = 10.3, 95% Cl [3.3-32.3]; P < 0.001). A subset of randomly selected An. gambiae s.l. (n = 518) was identified by polymerase chain reaction (PCR), among which 77.2% were An. merus, 22% were An. arabiensis, and the rest were not identified. We were also keen on identifying and describing the TEP1 genotypes of these mosquitoes, especially the *R3/R3 allele that was identified recently in the study area. We identified the following genotypes among An. merus: *R2/R2, *R3/R3, *R3/S2, S1/S1, and S2/S2. Among An. arabiensis, we identified R2/R2, S1/S1, and S2/S2. Tests on haplotype diversity showed that the most diverse allele was TEP1S1, followed by TEP1R2. Tajima's D values were positive for TEP1S1, indicating that there is a balancing selection, negative for TEP1R2, indicating there is a recent selective sweep, and as for TEP1R3, there was no evidence of selection. Phylogenetic analysis showed two distinct clades: refractory and susceptible alleles.
We find that the malaria vectors An. gambiae s.l. and An. funestus are predominantly exophilic. TEP1 genotyping for An. merus revealed five allelic combinations, namely *R2/R2, *R3/R3, *R3/S2, *S1/S1 and *S2/S2, while in An. arabiensis we only identified three allelic combinations: *R2/R2, *S1/S1, and S2/S2. The TEP1R3 allele was restricted to only An. merus among these sympatric mosquito species, and we find that there is no evidence of recombination or selection in this allele.
疟疾仍然是撒哈拉以南非洲最重要的传染病之一，2020 年导致约 2.28 亿例病例和 60.2 万例死亡。在该地区，疟疾传播主要由冈比亚按蚊和（最近）致倦库蚊复合体中的蚊子驱动。这些媒介的杀虫剂抗性和行为可塑性对疟疾控制的成果构成威胁。因此，需要开发替代方法，例如疟疾传播阻断疫苗或基因驱动系统。最近发现，含硫酯蛋白 1 (TEP1) 基因介导了疟原虫在蚊子中肠内的致死作用，这是一个很有前途的基因驱动系统靶点。在这里，我们研究了肯尼亚沿海野生疟疾病媒中 TEP1 等位基因的频率和分布。
使用室内和室外的 CDC 诱蚊灯在肯尼亚沿海的加泰村的 20 所房屋中收集蚊子。对蚊子进行解剖，并用不同的部分来确定它们的物种、血液来源和孢子状态。使用 R（v4.0.1）和 STATA（v17.0）对数据进行分析和可视化。
共收集了 18802 只蚊子，其中 77.8%（n=14631）为库蚊属，21.4%（n=4026）为冈比亚按蚊复合体，0.4%（n=67）为致倦库蚊，0.4%（n=78）为其他按蚊（库蚊、法属库蚊和预特库蚊）。收集的蚊子主要是外栖的，所有物种的户外捕获量都较高：库蚊属 93%（IRR=11.6，95%Cl[5.9-22.9]，P<0.001），冈比亚按蚊复合体 92%（IRR=7.2，95%Cl[3.6-14.5]，P<0.001），致倦库蚊 91%（IRR=10.3，95%Cl[3.3-32.3]，P<0.001）。随机选择的冈比亚按蚊复合体（n=518）的一个子集通过聚合酶链反应（PCR）进行鉴定，其中 77.2%为曼蚊，22%为阿蚊，其余未鉴定。我们还热衷于鉴定和描述这些蚊子的 TEP1 基因型，特别是最近在研究区域中发现的R3/R3 等位基因。在曼蚊中，我们鉴定出以下基因型：R2/R2、R3/R3、R3/S2、S1/S1 和S2/S2。在阿蚊中，我们鉴定出R2/R2、S1/S1 和S2/S2。单倍型多样性测试表明，最具多样性的等位基因是 TEP1S1，其次是 TEP1R2。TEP1S1 的 Tajima's D 值为正，表明存在平衡选择，TEP1R2 的 Tajima's D 值为负，表明存在近期的选择清除，而 TEP1R3 则没有证据表明存在选择。系统发育分析显示了两个不同的分支：抗性和易感等位基因。
我们发现，疟疾媒介冈比亚按蚊复合体和致倦库蚊主要是外栖的。对曼蚊的 TEP1 基因分型显示了五种等位基因组合，即*R2/R2、*R3/R3、*R3/S2、S1/S1 和S2/S2，而在阿蚊中我们只鉴定出三种等位基因组合：R2/R2、S1/S1 和S2/S2。这些共生蚊子物种中，TEP1R3 等位基因仅局限于曼蚊，我们发现该等位基因没有证据表明存在重组或选择。
