Exploiting a xenosurveillance approach on non-vector mosquitoes to detect malaria pathogens in Djibouti city

INTRODUCTION: Entomological surveillance is broadly applied to detect pathogens in mosquito vectorsand estimate the risk of exposure to mosquito-borne diseases. Irrespective to vector competence, bloodfedmosquitoes could also be used as “biological syringes” to highlight pathogen circulation in humanand animal populations (xenosurveillance) (Grubaugh et al., 2015. PLoS Negl Trop Dis, 9:e0003628).In this study, a xenosurveillance approach was applied in Djibouti to detect malaria parasites in bloodfednon-vector mosquitoes. After the introduction of the Asian vector, Anopheles stephensi, an increasein malaria cases is occurring in this area (Seyfarth et al., 2019. Parasitol Res, 118:725-32). The implementationof surveillance strategies is essential to prevent malaria outbreaks and a xenosurveillanceapproach could enhance early pathogen detection in areas where Anopheles vectors might be at lowdensities.MATERIALS AND METHODS: From January to February 2020, 11 sticky resting box (SRb) (Pombi etal., 2014. Parasit vectors, 7:247) and 12 bG-sentinel (bG-S) traps modified with a sugar feeding system(Manzi et al., 2023. Sci Rep, 13:12840) were deployed in Djibouti City. SRbs were serviced weekly,while bG-S worked for four consecutive days. Collected mosquitoes were morphologically identified todefine species and gonotrophic stage. All abdomens from fed culicine females (e. g., Culex and Aedesspp.) were analysed through DNA extraction (Rider et al., 2012. Malar J, 11:193) and PCR to definethe blood meal host (Kent and Norris, 2005. Am J Trop Med Hyg, 73:336-42); additionally Anophelesfemales were subjected to DNA extraction from head and thorax. DNA extracted from each mosquitogenus was further processed to detect plasmodium spp. through PCR and sequencing (Calzetta et al.,2018. Med vet Entomol, 32:372-77).RESULTS AND CONCLUSIONS: Overall, 14,378 mosquitoes were sampled during the study period;of these the 92.5% was collected with bG-S traps. Culicinae represented almost all of the total sampleand included Cx. quinquefasciatus (96.7%), Ae. aegypti (2.6%) and Cx. sitiens (0.2%). CollectedAnophelinae were An. stephensi (0.5%) and An. dthali (0.1%). The blood meal source was successfullyidentified in 26.4% of sample showing blood evidence (N: 500) and 46.9% of these fed on human hosts.No malaria parasites were detected in Anopheles species, which could be explained by the low numberof collected females (N: 36). Conversely, p. falciparum was detected in different dates (31thJan, 15thand 20th Feb) from six human-fed culicine mosquitoes (Cx. quinquefasciatus: 3 and Ae. aegypti: 3). Accordingto our findings, molecular detection of pathogens in blood fed non-vector mosquitoes makemalaria surveillance more feasible at low vector density. Enhancing surveillance is needed to reducemalaria burden and a xenosurveillance approach could be more effective in a low transmission context,such as in areas of new introduction or where eradication plans occur.