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bioRxiv2024

Entomological surveys and insecticide susceptibility profile of Aedes aegypti during the dengue outbreak in Sao Tome and Principe in 2022

BackgroundThe first dengue outbreak was reported in Sao Tome and Principe in 2022. This study was undertaken aiming to establish the typology of Aedes larval habitats, the distribution of Ae. aegypti and Ae. albopictus, the related entomological risk and the susceptibility profile of Ae. aegypti to insecticides for a better evidence-informed response. Methodology/Principal FindingsEntomological surveys were performed in all the seven health districts of Sao tome and Principe during the dry and rainy seasons in 2022. WHO tube and synergist assays using piperonyl butoxide (PBO) and diethyl maleate (DEM) were carried out and the genotyping of F1534C/V1016I/V410L mutations in Ae. aegypti. Aedes aegypti and Ae. albopictus were found in all seven health districts of the country with high prevalence of Ae. aegypti in the most urbanised district, Agua Grande. Both Aedes species bred mainly in used tyres, discarded tanks and water storage containers. In both survey periods, the Breteau (BI > 50), house (HI > 35%) and container (CI > 20%) indices were higher than threshold established by WHO to indicate high potential risk of dengue transmission. Aedes aegypti sample was susceptible to all insecticides tested except dichlorodiphenyltrichloroethane (DDT) (9.2% mortality), bendiocarb (61.4% mortality) and alpha-cypermethrin (97% mortality). A full recovery was reported in Ae. aegypti resistant to bendiocarb after pre-exposure to synergist PBO. Only one Ae. aegypti specimen was found carrying F1534C mutation. Conclusions/SignificanceThese findings revealed at high potential risk for dengue transmission throughout the year, with the bulk of larval breeding occurring in used tyres, water storage and discarded containers. Most of the insecticides tested remain effective to control Aedes vectors in Sao Tome except DDT and bendiocarb. These data underline the importance to raise community awareness and to implement routine dengue vector control strategies to prevent further outbreaks in Sao Tome and Principe, and elsewhere in the subregion. Author SummaryDuring the first dengue outbreak reported in Sao Tome and Principe in 2022, entomological investigations were undertaken aiming to establish the typology of Aedes larval habitats, the distribution of Ae. aegypti and Ae. albopictus, the related entomological risk and the susceptibility profile of Ae. aegypti to insecticides for a better evidence-informed response. The results revealed the presence of Ae. aegypti and Ae. albopictus in all seven health districts of the country with high prevalence of Ae. aegypti in the most urbanised district, Agua Grande. Both Aedes species bred mainly in used tyres, discarded tanks and water storage containers suggesting a good waste management and improving water supply system could help to reduce Aedes densities and the risk of dengue transmission. Analyses also revealed that most of the insecticides tested remain effective to control Aedes vectors in Sao Tome except dichlorodiphenyltrichloroethane and bendiocarb. These findings revealed at high potential risk for dengue transmission throughout the year and underline the importance to raise community awareness and to implement routine dengue vector control strategies to prevent further outbreaks in Sao Tome and Principe, and elsewhere in the subregion.

zoology↗

bioRxiv2021

CRISPR-mediated knock-in of transgenes into the malaria vector Anopheles funestus

The ability to introduce mutations, or transgenes, of choice to precise genomic locations has revolutionised our ability to understand how genes and organisms work. In many mosquito species that are vectors of various human disease, the advent of CRISPR genome editing tools has shed light on basic aspects of their biology that are relevant to their efficiency as disease vectors. This allows a better understanding of how current control tools work and opens up the possibility of novel genetic control approaches, such as gene drives, that deliberately introduce genetic traits into populations. Yet for the Anopheles funestus mosquito, a significant vector of malaria in sub-Saharan Africa and indeed the dominant vector species in many countries, transgenesis has yet to be achieved. We describe herein an optimised transformation system based on the germline delivery of CRISPR components that allows efficient cleavage of a previously validated genomic site and preferential repair of these cut sites via homology-directed repair (HDR), which allows introduction of exogenous template sequence, rather than end-joining repair. The rates of transformation achieved are sufficiently high that it should be able to introduce alleles of choice to a target locus, and recover these, without the need to include additional dominant marker genes. Moreover, the high rates of HDR observed suggest that gene drives, which employ an HDR-type mechanism to ensure their proliferation in the genome, may be well suited to work in An. funestus.

genetics↗