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Aedes aegypti mosquitoes are primary vectors that carry mosquito-borne diseases such as
dengue fever, Zika and Yellow fever. Despite mosquito control measures employed in
Tanzania such as indoor residual spraying and larvae source management systems, several
studies have reported the presence of insecticide resistance. The present study aimed at
investigating the abundance of Ae. aegypti and their susceptibility to pyrethroids in
Muheza district in Tanga region. A total of 7200 mosquito larvae were collected from
selected wards in Muheza district using standard dipping method and reared into adults.
Some of the reared larvae died and others escaped during the rearing process leaving 2572
of the collected larvae that emerged into adults. Adult mosquitoes were identified using
standard taxonomic keys. Female Ae. aegypti mosquitoes aged three to five days old were
tested for susceptibility to pyrethroids using WHO guidelines and the insecticides used
were permethrin (0.75%), alphacypermethrin (0.05%) and deltamethrin (0.05%).
Mosquito DNA was then extracted and voltage-gated sodium channel genes were
amplified targeting Domain II and Domain III yielding expected amplicons size of 640
and 740 bp, respectively. Abundant Ae. Aegypti species were from Mbaramo ward
representing 21% (n=267), followed by Zeneti representing 19% (n=240), Kwafungo 19%
(n=236), Genge 13% (n=161), Ngomeni 12% (n=153), Misozwe 10% (n=131) and Magila
6% (n=78). Tested Ae. aegypti mosquitoes were susceptible to alphacypermethrin and
permethrin with a percentage mortality of 100 and 98.75%, respectively, and resisted to
deltamethrin with a percentage mortality of 68%. S989P and V1016I point mutations
were identified. Increase in Ae. aegypti resistance to deltamethrin is attributed to
prolonged use of insecticides as residual sprays and on pyrethroids impregnated bed nets.
Ae. aegypti resistance to deltamethrin and high abundance of this specie in some wards
pose a high risk for mosquito-borne diseases and this calls for rational vector control
measures. |
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