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Polius Gerazi Pinda
Ifakara Health Institute
Corresponding Author
ORCiD: https://orcid.org/0000-0002-9167-1672
Fredros O Okumu
Ifakara Health Institute
Corresponding Author
ORCiD: https://orcid.org/0000-0003-2731-5654
License:
This work is licensed under a CC BY 4.0 License. Read Full License
Background: Long-lasting insecticide-treated nets (LLINs) and indoor residual spraying (IRS) have greatly reduced malaria transmission in sub-Saharan Africa, but are threatened by insecticide resistance in dominant malaria vectors. In south-eastern Tanzania, pyrethroid-resistant Anopheles funestus now transmit more than 80% of malaria infections even in villages where the species occurs at far lower densities than other vectors such as Anopheles arabiensis.
Methods: To better understand the dominance of An. funestus in these settings and improve options for its control, this study compared intensities of resistance between females of this species and those of An. arabiensis , using WHO assays with 1×, 5× and 10× insecticide doses. Additional tests were done to assess the reversibility of such resistance using synergists. The mosquitoes were collected from villages across two districts in south-eastern Tanzania.
Findings: Both species were resistant to the two pyrethroids (permethrin and deltamethrin) and the organochloride (DDT) but susceptible to the organophosphate (pirimiphos-methyl) at standard baseline doses (1×). However, An. funestus as opposed to An. arabiensis was also resistant to the carbamate (bendiocarb) at standard doses (1×). An. funestus showed strong resistance to pyrethroids, surviving the 5× doses and 10× doses except in one village. Pre-exposure to the synergist, piperonyl butoxide (PBO), reversed the pyrethroid-resistance in both An. arabiensis and An. funestus achieving mortalities >98%, except for An. funestus from two villages for which permethrin-associated mortalities exceeded 90% but not 98%.
Conclusions : In these communities where An. funestus now dominates malaria transmission, the species also displays much stronger resistance to pyrethroids than its counterpart, An. arabiensis, and can readily survive more classes of insecticides, including carbamates. The resistance to pyrethroids in both mosquito species appears to be mostly metabolic and can be reversed significantly using synergists such as PBO. These findings may explain the continued persistence and dominance of An. funestus despite widespread use of pyrethroid-treated LLINs, and will also inform future choices of interventions to tackle malaria transmission in this area and other similar settings. Such interventions may include PBO-based LLINs or improved IRS with compounds such as organophosphates against which the vectors are still susceptible.
Keywords
Insecticide resistance, Anopheles funestus, PBO, Ifakara Health Institute, Tanzania
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CURRENT STATUS: Published
View the published article at Malaria Journal.
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Editorial decision: Accept
On 04 Nov, 2020
Editor assigned
On 03 Nov, 2020
Submission checks complete
On 03 Nov, 2020
Editor invited
On 03 Nov, 2020
No comments provided
Editorial decision: Minor Revision
On 28 Oct, 2020
Reviewers invited
Invitations sent on 23 Jun, 2020
Editor assigned
On 17 Jun, 2020
Submission checks complete
On 16 Jun, 2020
Editor invited
On 16 Jun, 2020
Version 1
Posted 31 Mar, 2020
No comments provided
Editorial decision: Major Revision
On 08 Jun, 2020
Review #2 received
Received 19 May, 2020
Review #1 received
Received 24 Apr, 2020
Reviewer #2 agreed
On 14 Apr, 2020
Reviewers invited
Invitations sent on 03 Apr, 2020
Reviewer #1 agreed
On 03 Apr, 2020
Editor assigned
On 27 Mar, 2020
First submitted
On 26 Mar, 2020
Submission checks complete
On 26 Mar, 2020
Editor invited
On 26 Mar, 2020
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Subject Areas
Infectious Diseases
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A new preprint design is coming!
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See the published version of this preprint at Malaria Journal.
This is a preprint, a preliminary version of a manuscript that has not completed peer review at a journal. Research Square does not conduct peer review prior to posting preprints. The posting of a preprint on this server should not be interpreted as an endorsement of its validity or suitability for dissemination as established information or for guiding clinical practice.
Learn more about In Review
Research
Polius Gerazi Pinda
Ifakara Health Institute
Corresponding Author
ORCiD: https://orcid.org/0000-0002-9167-1672
Fredros O Okumu
Ifakara Health Institute
Corresponding Author
ORCiD: https://orcid.org/0000-0003-2731-5654
Badges
Prescreen
This manuscript passed our Prescreen assessment
Complete author information
Appropriate declaration statements
Potential risks to human health
Prescreen
Peer Review Timeline
CURRENT STATUS: Published
View the published article at Malaria Journal.
No community comments so far
Editorial decision: Accept
On 04 Nov, 2020
Editor assigned
On 03 Nov, 2020
Submission checks complete
On 03 Nov, 2020
Editor invited
On 03 Nov, 2020
No comments provided
Editorial decision: Minor Revision
On 28 Oct, 2020
Reviewers invited
Invitations sent on 23 Jun, 2020
Editor assigned
On 17 Jun, 2020
Submission checks complete
On 16 Jun, 2020
Editor invited
On 16 Jun, 2020
Version 1
Posted 31 Mar, 2020
No comments provided
Editorial decision: Major Revision
On 08 Jun, 2020
Review #2 received
Received 19 May, 2020
Review #1 received
Received 24 Apr, 2020
Reviewer #2 agreed
On 14 Apr, 2020
Reviewers invited
Invitations sent on 03 Apr, 2020
Reviewer #1 agreed
On 03 Apr, 2020
Editor assigned
On 27 Mar, 2020
First submitted
On 26 Mar, 2020
Submission checks complete
On 26 Mar, 2020
Editor invited
On 26 Mar, 2020
Metrics
Comments: 0
PDF Downloads: ...
HTML Views: ...
Subject Areas
Infectious Diseases
License:
This work is licensed under a CC BY 4.0 License. Read Full License
View the published article at Malaria Journal.
Background: Long-lasting insecticide-treated nets (LLINs) and indoor residual spraying (IRS) have greatly reduced malaria transmission in sub-Saharan Africa, but are threatened by insecticide resistance in dominant malaria vectors. In south-eastern Tanzania, pyrethroid-resistant Anopheles funestus now transmit more than 80% of malaria infections even in villages where the species occurs at far lower densities than other vectors such as Anopheles arabiensis.
Methods: To better understand the dominance of An. funestus in these settings and improve options for its control, this study compared intensities of resistance between females of this species and those of An. arabiensis , using WHO assays with 1×, 5× and 10× insecticide doses. Additional tests were done to assess the reversibility of such resistance using synergists. The mosquitoes were collected from villages across two districts in south-eastern Tanzania.
Findings: Both species were resistant to the two pyrethroids (permethrin and deltamethrin) and the organochloride (DDT) but susceptible to the organophosphate (pirimiphos-methyl) at standard baseline doses (1×). However, An. funestus as opposed to An. arabiensis was also resistant to the carbamate (bendiocarb) at standard doses (1×). An. funestus showed strong resistance to pyrethroids, surviving the 5× doses and 10× doses except in one village. Pre-exposure to the synergist, piperonyl butoxide (PBO), reversed the pyrethroid-resistance in both An. arabiensis and An. funestus achieving mortalities >98%, except for An. funestus from two villages for which permethrin-associated mortalities exceeded 90% but not 98%.
Conclusions : In these communities where An. funestus now dominates malaria transmission, the species also displays much stronger resistance to pyrethroids than its counterpart, An. arabiensis, and can readily survive more classes of insecticides, including carbamates. The resistance to pyrethroids in both mosquito species appears to be mostly metabolic and can be reversed significantly using synergists such as PBO. These findings may explain the continued persistence and dominance of An. funestus despite widespread use of pyrethroid-treated LLINs, and will also inform future choices of interventions to tackle malaria transmission in this area and other similar settings. Such interventions may include PBO-based LLINs or improved IRS with compounds such as organophosphates against which the vectors are still susceptible.
Figure 1
Figure 2
Figure 3
Figure 4
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