KEMRI-Centre for Geographic Medicine Research Coast, Kilifi, Kenya.
Eastern and Southern Africa Centre of International Parasite Control, Nairobi, Kenya.
Parasit Vectors. 2024 Oct 9;17(1):425. doi: 10.1186/s13071-024-06513-0.
Lymphatic filariasis (LF) is an infectious neglected tropical disease caused by mosquito-borne nematodes such as Wuchereria bancrofti, Brugia malayi, and Brugia timori. Globally, LF affects 51 million people, with approximately 863 million at risk in 47 countries. In Kenya, filariasis is endemic along the entire coastal strip, and more recently, at the Kenya-Ugandan border. The World Health Organization (WHO) recommends mass drug administration to reduce disease transmission and morbidity. Monitoring the effectiveness of such interventions relies on robust surveillance, achieved through microscopic examination of microfilariae in nighttime blood, detection of circulating filarial antigens (CFA), and molecular xenomonitoring. We focused on molecular xenomonitoring along the Kenyan coast due to its noninvasive nature and the opportunity to identify new vectors.
In 2022, mosquitoes were collected from Kilifi, Kwale, and Taita-Taveta counties located within the LF endemic region in Kenya. Subsequently, genomic deoxyribonucleic acid (gDNA) was extracted from these mosquitoes for speciation and analysis of Wuchereria bancrofti infection rates. The impact of sociodemographic and household attributes on infection rates was assessed using generalized estimating equations.
A total of 18,121 mosquitoes belonging to Culicinae (63.0%, n = 11,414) and Anophelinae (37.0%, n = 6707) subfamilies were collected. Morphological identification revealed that Anopheline mosquitoes were dominated by An. funestus (45.4%, n = 3045) and An. gambiae (42.8%, n = 2873). Wuchereria bancrofti infection rates were highest in Kilifi (35.4%; 95% CI 28.0-43.3%, n = 57/161) and lowest in Taita Taveta (5.3%; 95% CI 3.3-8.0%, n = 22/412). The major vectors incriminated are An. rivulorum, An. funestus sensu stricto, and An. arabiensis. Mosquitoes of the An. funestus complex were significantly associated with LF transmission (OR 18.0; 95% CI 1.80-180; p = 0.014). Additionally, a higher risk of transmission was observed outdoors (OR 1.74; 95% CI 1.08-2.82; p = 0.024) and in homesteads that owned livestock (OR 2.00; 95% CI 1.09-3.66; p = 0.025).
In this study, we identified An. funestus s.l. sibling species, An. rivulorum and An. funestus s.s., as the primary vectors of lymphatic filariasis along the Kenyan coast. These findings also highlight that a significant portion of disease transmission potentially occurs outdoors where indoor-based vector control tools, including long-lasting insecticidal nets and indoor residual spray, may not be effective. Therefore, control measures targeting outdoor resting mosquitoes such as zooprophylaxis, larval source management, and attractive sugar baits may have potential for LF transmission reduction.
淋巴丝虫病（LF）是一种由蚊媒传播的热带传染病，由班氏丝虫、马来丝虫和帝汶丝虫等线虫引起。在全球范围内，有 5100 万人受到 LF 的影响，在 47 个国家中，约有 8.63 亿人面临感染风险。在肯尼亚，整个沿海地带都存在丝虫病，最近在肯尼亚和乌干达边境也出现了这种疾病。世界卫生组织（WHO）建议采用大规模药物治疗来减少疾病传播和发病率。监测此类干预措施的效果依赖于强有力的监测，这可以通过夜间血液中的微丝蚴显微镜检查、循环丝状抗原（CFA）检测和分子虫媒监测来实现。我们专注于肯尼亚沿海地区的分子虫媒监测，因为这种方法具有非侵入性，可以识别新的传播媒介。
2022 年，我们从肯尼亚淋巴丝虫病流行地区的基利菲、夸莱和泰塔塔维塔县收集了蚊子。随后，从这些蚊子中提取基因组脱氧核糖核酸（gDNA）进行种系分析和班氏丝虫感染率分析。使用广义估计方程评估社会人口和家庭属性对感染率的影响。
共收集到 18121 只属于库蚊科（63.0%，n=11414）和按蚊科（37.0%，n=6707）亚科的蚊子。形态学鉴定表明，按蚊主要由致倦库蚊（45.4%，n=3045）和冈比亚按蚊（42.8%，n=2873）组成。基利菲的班氏丝虫感染率最高（35.4%；95%置信区间 28.0-43.3%，n=57/161），而泰塔塔维塔的感染率最低（5.3%；95%置信区间 3.3-8.0%，n=22/412）。主要的传播媒介包括致倦库蚊、致倦库蚊指名亚种和阿巴蚊。致倦库蚊复合体的蚊子与 LF 传播显著相关（OR 18.0；95%置信区间 1.80-180；p=0.014）。此外，户外（OR 1.74；95%置信区间 1.08-2.82；p=0.024）和拥有牲畜的住家（OR 2.00；95%置信区间 1.09-3.66；p=0.025）的蚊子传播风险更高。
在本研究中，我们确定了致倦库蚊 s.l. 姊妹种、致倦库蚊和致倦库蚊指名亚种，是肯尼亚沿海地区淋巴丝虫病的主要传播媒介。这些发现还表明，疾病传播的很大一部分可能发生在户外，室内基控制虫媒的工具，包括长效杀虫剂处理蚊帐和室内滞留喷洒，可能效果不佳。因此，针对户外休息蚊子的控制措施，如动物媒介防治、幼虫源管理和诱捕糖饵，可能具有降低 LF 传播的潜力。
