Preliminary sampling of mosquito vectors and pathogens in Djibouti City using a novel surveillance method based on FTA-card

INTRODUCTION: Several strategies are available in mosquito-borne disease surveillance, according to the objective, target species, available funding and skills of personnel. In this study, we modified a bG sentinel trap to include a sugar delivery system equipped with a nucleic acid preserving substrate (fTa card). during sugar feeding, pathogens in mosquito saliva are released on a honey-soaked fTa card, remaining detectable for several days at environmental conditions. This approach simplifies surveillance procedures in pathogen detection, decreasing time, cost and labour required, and avoiding cold chain (hall-mendelin et al., 2010. PnaS, 107: 11255-59). MATERIALS AND METHODS: we deployed 12 bG sentinel traps modified with honey-baited fTa cards in djibouti City (djibouti) placing traps outdoors in an Italian military base where pyrethroid insecticides are used. In each site, we performed six weekly captures (from 28th January 2020 to 25th february 2020) maintaining traps active for 3-4 consecutive days. mosquitoes and fTa cards collected from each trap were stored in silica gel at room temperature until further analysis in Italy. all mosquitoes were morphologically identified by species, and rna extracted from fTa cards was tested for the presence of arboviruses by real time PCr and sequencing (Scaramozzino et al., 2002. J Clin microbiol, 39(5):1922–27; Pastorino et al., 2005. J virol methods, 124: 65–71; drosten et al., 2002. J Clin microbiol, 40:2323–30). a mosquito subsample was also genotyped through dna extraction (rider at al., 2012. malar J, 11: 193) and PCr to assess the presence of mutations for knockdown resistance (kdr) to pyrethroids (martinez-Torres et al., 1999. Pestic Sci, 55:1012-20). RESULTS AND CONCLUSIONS: out of 13,304 collected mosquitoes, 98.7% were identified as follows: 96.8% Culex pipiens/quinquefasciatus, 2.7% Aedes aegypti, 0.36% Anopheles stephensi, 0.11% Culex sitiens and 0.05% Anopheles dthali. despite the control efforts taken over the years against An. stephensi, this invasive asian malaria vector was detected, confirming its establishment in horn of africa. we also show for the first time An. dthali in djibouti City, a secondary malaria vector known to be present in the north of the country (uGP Pnud/ministere de la Santé, republique de djibouti, PnlP 2020-2024). The high density of Cx. pipiens/quinquefasciatus in the study area can be explained by high levels of insecticide resistance observed on a mosquito subsample (no.= 133): homozygous resistant 84%; heterozygous 12.5%; homozygous susceptible 3.5%. finally, 3 of 71 fTa cards detected west nile (no.= 2) and dengue (no.= 1) viruses according with the presence of vectors in the same trap. These findings suggest that the proposed sampling approach could be applied for mosquito pathogens surveillance, resulting particularly useful in remote areas and in long term storage, when laboratory and qualified personnel are not available in loco, but also to reducing efforts in pathogen detection.