Abstract
Background Aedes aegypti and Ae. albopictus are the main epidemic vectors of dengue, chikungunya and Zika viruses worldwide. Their control during epidemics relies mainly on control of larvae and adults with insecticides. Unfortunately, loss of susceptibility of both species to several insecticide classes limits the efficacy of interventions. In Africa, where Aedes-borne viruses are of growing concern, few data are available on resistance to insecticides. To fill this gap, we assessed the susceptibility to insecticides of Ae. aegypti and Ae. albopictus populations in the Central African Republic (CAR) and studied the mechanisms of resistance.MethodsImmature stages were sampled between June and September 2014 in six locations in Bangui (the capital of CAR) for larval and adult bioassays according to WHO standard procedures. We also characterized DDT- and pyrethroid-resistant mosquitoes molecularly and biochemically, including tests for the activities of nonspecific esterases (α and β), mixed-function oxidases, insensitive acetylcholinesterase and glutathione S-transferases.ResultsLarval bioassays, carried out to determine the lethal concentrations (LC50 and LC95) and resistance ratios (RR50 and RR95), suggested that both vector species were susceptible to Bacillus thuringiensis var. israeliensis and to temephos. Bioassays of adults showed susceptibility to propoxur and fenitrothion, except for one Ae. albopictus population that was suspected to be resistant to fenithrothion. None of the Ae. aegypti populations was fully susceptible to DDT. Ae. albopictus presented a similar profile to Ae. aegypti but with a lower mortality rate (41%). Possible resistance to deltamethrin was observed among Ae. aegypti and Ae. albopictus, although some were susceptible. No kdr mutations were detected in either species; however, the activity of detoxifying enzymes was higher in most populations than in the susceptible Ae. aegypti strain, confirming decreased susceptibility to DDT and deltamethrin.ConclusionThese findings suggested that regular, continuous monitoring of resistance is necessary in order to select the most effective adulticides for arbovirus control in Bangui.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-016-1887-5) contains supplementary material, which is available to authorized users.
Highlights
Aedes aegypti and Ae. albopictus are the main epidemic vectors of dengue, chikungunya and Zika viruses worldwide
This insecticide was used moderately in Central Africa (Cameroon and Gabon) in the 1970s [38], it had never been used in vector control programmes in Central African Republic (CAR), which probably explains the full susceptibility we observed for both species
We describe for the first time the susceptibility of Aedes in CAR to the main insecticide classes and the mechanisms potentially involved in resistance
Summary
Aedes aegypti and Ae. albopictus are the main epidemic vectors of dengue, chikungunya and Zika viruses worldwide. Their control during epidemics relies mainly on control of larvae and adults with insecticides. Aedes aegypti is native to Africa and is found throughout the tropics, whereas Ae. albopictus is native to Asia but has recently spread to all continents These three viruses are increasing global health threats, spreading from their original niches to most areas of the world. ZIKV, which was originally isolated in 1947 from a monkey in Uganda [5], has occasionally been reported in humans in Africa and Asia [6], but, after its sudden emergence in 2007 on Yap Island, affecting about 5,000 people [7], it caused successive outbreaks in French Polynesia in 2013–2014 [8] and in Brazil since October 2015, before spreading across Latin America [9]. The recrudescence of ZIKV has been associated with reports of neurological disorders and microcephaly, and the World Health Organization (WHO) declared it a “public health emergency of international concern” on 1 February 2016 [10]
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