The role of molecular xenomonitoring for assessing the impact of Ivermectin, Diethylcarbamazine Citrate and Albendazole triple-drug treatment against lymphatic filariasis: A cross-sectional study in the Kenyan coastal region.

Lymphatic Filariasis (LF) is a mosquito-borne disease primarily caused by the filarial parasite Wuchereria bancrofti. The triple-drug therapy of Ivermectin, Diethylcarbamazine Citrate and Albendazole (IDA) has been adopted to accelerate LF elimination of LF as a public health problem, particularly in areas where onchocerciasis is not co-endemic. In Kenya, IDA was administered to endemic communities in Jomvu sub-County (Mombasa) and Lamu County in 2018 and 2019. The impact of IDA was assessed using Molecular Xenomonitoring (MX), which involves detecting W. bancrofti DNA in mosquito pools via quantitative PCR (qPCR). MX surveys were conducted at baseline (2018) and at IDA impact survey 1 (IIS-1) in 2021 after two treatment rounds. Mosquitoes were collected from 30 randomly and 5-9 purposively selected villages per area. Traps used included CDC light, Gravid, and BioGents (BG) traps at baseline, and only CDC light and Gravid traps at IIS-1. Mosquitoes were sorted by genus and pooled in up to 25 per pool. DNA was extracted and analyzed by qPCR. Filarial DNA prevalence was estimated using PoolTools v0.1.4. Concurrently, human infection was assessed using filariasis test strips (FTS) to detect circulating filarial antigen (CFA). At baseline, 37,732 mosquitoes were collected: 0.07% Anopheles, 2.3% Aedes, and 97.6% Culex. Of 486 pools tested, 30 (0.26%) were positive for W. bancrofti DNA. At IIS-1, 71,634 mosquitoes were collected: 0.46% Anopheles and 99.5% Culex. Of 1,695 pools tested, 22 (0.06%) were positive. Significant reductions were observed in filarial DNA in mosquitoes (76.9%, p < 0.001) and human antigenemia (52.1%, p = 0.004) after two treatment rounds. This study demonstrates a substantial decline in LF infection following two rounds of IDA. It also highlights molecular xenomonitoring as a sensitive and non-invasive tool for monitoring LF elimination progress. We recommend its integration into national LF control programs as a complementary surveillance method post-MDA.