Xenomonitoring as an epidemiological tool adjunct to post-stop surveillance of albendazole ivermectin mass drug distribution in the Bougouni -Yanfolila evaluation unit in the Sikasso, Mali in 2023

Introduction: Mali and Guinea share a border and are endemic to lymphatic filariasis (LF), however each country is at a distinct level in its LF elimination efforts. Mali is in the LF transmission assessment survey (TAS) phase, whereas Guinea is still implementing the mass drug administration. In the Bougouni-Yanfolila Evaluation Unit (EU), this study assessed XenoFil (combinaison of xenomonitoring plus health facilities-based Ag detection) as an LF transmission surveillance tool to track the emergence of LF in cross-border areas following TAS3. Method: In the Bougouni-Yanfolila EU, we conducted a cross-sectional study to gather mosquitoes in the villages and blood samples from participants of six years of age and older. In June, August 2022, and January 2023, we conducted three entomological studies in two ecologically distinct villages. The Ifakara type C tent trap, the gravid trap, and intra-household pyrethrum spraying were used to gather mosquitoes. For qPCR, we sorted the same mosquitoes species into batches of twenty. PoolScreen® 2 was used to determine the prevalence of infection. Trained local health workers performed serological surveys using filariasis test strips. Results: In the two study villages, 989 Anopheles gambiae complex and 3743 Culex spp . were collected out of 4732 mosquitoes . Culex spp . accounted for 79.92% (211/264) of the 264 pools, while the Anopheles gambiae complex made up 20.08 (53/264). In June 2022, only one pool (0.53%) of Culex spp . tested positive [95% CI: 0.01-2.89]. Positive Anopheles pools were absent. The blood of ten of the 2056 individuals had positive results [0.49% (10/2056)]. Among the positives, one belonged to 6-7 years, two to that of 8-17 years, and seven to that of 18 years and older. Of the positive volunteers, 0.6% (6/996) were from Yanfolila's border health region. Conclusion: The new XenoFil approach proved to be an easy, effective, and relatively cheaper method for integrated LF surveillance in rural areas, with an average cost of 5,656,244 CFA (US$9,070) for XenoFil (entomology-serology) and 6,366,450 CFA (US$10,209) for TAS in one survey in one EU. From the perspective of integrated LF monitoring, XenoFil is needed for scaling up to other EU.