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Susceptibility profile and metabolic mechanisms involved in Aedes aegypti and Aedes albopictus resistant to DDT and deltamethrin in the Central African Republic

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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.

Methods: Immature 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.

Results: Larval 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.

Conclusion: These 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 material: The online version of this article (doi:10.1186/s13071-016-1887-5) contains supplementary material, which is available to authorized users.

No MeSH data available.


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Activity profiles of non-specific α- and β-esterases and mixed-function oxidases (cytochrome P450) in Ae. aegypti (a, c, e) and Ae. albopictus (b, d, f). Numbers in parentheses indicate the number of mosquitoes assayed. Asterisks indicate significant increase in wild populations compared to SBE susceptible strain values (P < 0.05, Mann-Whitney tests). Abbreviations: SBE, Benin strain; IPB, Institut Pasteur de Bangui; NES, non-specific esterase; MFO, mixed-function oxidase
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Fig2: Activity profiles of non-specific α- and β-esterases and mixed-function oxidases (cytochrome P450) in Ae. aegypti (a, c, e) and Ae. albopictus (b, d, f). Numbers in parentheses indicate the number of mosquitoes assayed. Asterisks indicate significant increase in wild populations compared to SBE susceptible strain values (P < 0.05, Mann-Whitney tests). Abbreviations: SBE, Benin strain; IPB, Institut Pasteur de Bangui; NES, non-specific esterase; MFO, mixed-function oxidase

Mentions: For each of the four enzyme systems tested, we analysed at least 25 individuals per species and per population (Figs. 2 and 3). Comparisons with the SBE strain showed significant differences (Mann-Whitney U-test, P < 0.05) in mean enzyme activity in some populations: α-esterase activities were significantly higher in two Ae. albopictus populations (IPB, U = 140, Z = 4.84, P < 0.0001, and Sica 1, U = 216, Z = 3.32, P = 0.0009), and β-esterase activities were significantly higher in all five populations of Ae. aegypti (IPB,U = 429.5, Z = 1.98, P = 0.04; Sica 1, U = 284, Z = 2.3, P = 0.02; Lakouanga, U = 258, Z = 2.69, P = 0.007; Ouango, U = 214.5, Z = 3.34, P = 0.0008; and Ngongonon 3, U = 230.5, Z = 3.1, P = 0.001) and three Ae. albopictus populations (IPB, U = 118, Z = 5.14, P < 0.0001; Sica 1, U = 84, Z = 5.3, P < 0.0001; and Lakouanga, U = 168, Z = 4.04, P = 0.0001.Fig. 2


Susceptibility profile and metabolic mechanisms involved in Aedes aegypti and Aedes albopictus resistant to DDT and deltamethrin in the Central African Republic
Activity profiles of non-specific α- and β-esterases and mixed-function oxidases (cytochrome P450) in Ae. aegypti (a, c, e) and Ae. albopictus (b, d, f). Numbers in parentheses indicate the number of mosquitoes assayed. Asterisks indicate significant increase in wild populations compared to SBE susceptible strain values (P < 0.05, Mann-Whitney tests). Abbreviations: SBE, Benin strain; IPB, Institut Pasteur de Bangui; NES, non-specific esterase; MFO, mixed-function oxidase
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC5121976&req=5

Fig2: Activity profiles of non-specific α- and β-esterases and mixed-function oxidases (cytochrome P450) in Ae. aegypti (a, c, e) and Ae. albopictus (b, d, f). Numbers in parentheses indicate the number of mosquitoes assayed. Asterisks indicate significant increase in wild populations compared to SBE susceptible strain values (P < 0.05, Mann-Whitney tests). Abbreviations: SBE, Benin strain; IPB, Institut Pasteur de Bangui; NES, non-specific esterase; MFO, mixed-function oxidase
Mentions: For each of the four enzyme systems tested, we analysed at least 25 individuals per species and per population (Figs. 2 and 3). Comparisons with the SBE strain showed significant differences (Mann-Whitney U-test, P < 0.05) in mean enzyme activity in some populations: α-esterase activities were significantly higher in two Ae. albopictus populations (IPB, U = 140, Z = 4.84, P < 0.0001, and Sica 1, U = 216, Z = 3.32, P = 0.0009), and β-esterase activities were significantly higher in all five populations of Ae. aegypti (IPB,U = 429.5, Z = 1.98, P = 0.04; Sica 1, U = 284, Z = 2.3, P = 0.02; Lakouanga, U = 258, Z = 2.69, P = 0.007; Ouango, U = 214.5, Z = 3.34, P = 0.0008; and Ngongonon 3, U = 230.5, Z = 3.1, P = 0.001) and three Ae. albopictus populations (IPB, U = 118, Z = 5.14, P < 0.0001; Sica 1, U = 84, Z = 5.3, P < 0.0001; and Lakouanga, U = 168, Z = 4.04, P = 0.0001.Fig. 2

View Article: PubMed Central - PubMed

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.

Methods: Immature 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 (&alpha; and &beta;), mixed-function oxidases, insensitive acetylcholinesterase and glutathione S-transferases.

Results: Larval 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.

Conclusion: These 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 material: The online version of this article (doi:10.1186/s13071-016-1887-5) contains supplementary material, which is available to authorized users.

No MeSH data available.


Related in: MedlinePlus