Autor/a:
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Glunt, Katey D.; Abilio, Ana Paula; Bassat Orellana, Quique; Bulo, Helder; Gilbert, Allison E.; Huijben, Silvie; Manaca, Maria Nélia; Macete, Eusébio; Alonso, Pedro; Paaijmans, Krijn P.
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Abstract:
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BACKGROUND: Chemical insecticides are crucial to malaria control
and elimination programmes. The frontline vector control
interventions depend mainly on pyrethroids; all long-lasting
insecticidal nets (LLINs) and more than 80% of indoor residual
spraying (IRS) campaigns use chemicals from this class. This
extensive use of pyrethroids imposes a strong selection pressure
for resistance in mosquito populations, and so continuous
resistance monitoring and evaluation are important. As
pyrethroids have also been used for many years in the Manhica
District, an area in southern Mozambique with perennial malaria
transmission, an assessment of their efficacy against the local
malaria vectors was conducted. METHODS: Female offspring of
wild-caught Anopheles funestus s.s. females were exposed to
deltamethrin, lambda-cyhalothrin and permethrin using the World
Health Organization (WHO) insecticide-resistance monitoring
protocols. The 3-min WHO cone bioassay was used to evaluate the
effectiveness of the bed nets distributed or available for
purchase in the area (Olyset, permethrin LLIN; PermaNet 2.0,
deltamethrin LLIN) against An. funestus. Mosquitoes were also
exposed to PermaNet 2.0 for up to 8 h in time-exposure assays.
RESULTS: Resistance to pyrethroids in An. funestus s.s. was
extremely high, much higher than reported in 2002 and 2009. No
exposure killed more than 25.8% of the mosquitoes tested
(average mortality, deltamethrin: 6.4%; lambda-cyhalothrin:
5.1%; permethrin: 19.1%). There was no significant difference in
the mortality generated by 3-min exposure to any net (Olyset:
9.3% mortality, PermaNet 2.0: 6.0%, untreated: 2.0%; p = 0.2).
Six hours of exposure were required to kill 50% of the An.
funestus s.s. on PermaNet 2.0. CONCLUSIONS: Anopheles funestus
s.s. in Manhica is extremely resistant to pyrethroids, and this
area is clearly a pyrethroid-resistance hotspot. This could
severely undermine vector control in this district if no
appropriate countermeasures are undertaken. The National Malaria
Control Programme (NMCP) of Mozambique is currently improving
its resistance monitoring programme, to design and scale up new
management strategies. These actions are urgently needed, as the
goal of the NMCP and its partners is to reach elimination in
southern Mozambique by 2020. |