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Patterns of human exposure to malaria vectors in Zanzibar and implications for malaria elimination efforts
April Monroe
Johns Hopkins University
Corresponding Author
ORCiD: https://orcid.org/0000-0002-8959-6837
License:
This work is licensed under a CC BY 4.0 License. Read Full License
View the published version at Malaria Journal.
Background Zanzibar provides a good case study for malaria elimination. The islands have experienced a dramatic reduction in malaria burden since the introduction of effective vector control interventions and case management. Malaria prevalence has now been maintained below 1% for the past decade and the islands can feasibly aim for elimination.
Methods To better understand factors that may contribute to remaining low-level malaria transmission in Zanzibar, layered human behavioural and entomological research was conducted between December 2016 and December 2017 in 135 randomly selected households across six administrative wards. The study included: 1) household surveys, 2) structured household observations of nighttime activity and sleeping patterns, and 3) paired indoor and outdoor mosquito collections. Entomological and human behavioural data were integrated to provide weighted estimates of exposure to vector bites, accounting for proportions of people indoors or outdoors, and protected by insecticide-treated nets (ITNs) each hour of the night.
Results Overall, 92% of female Anopheles mosquitoes were caught in the rainy season compared to 8% in the dry season and 72% were caught outdoors compared to 28% indoors. For individual ITN users, ITNs prevented an estimated two-thirds (66%) of exposure to vector bites and nearly three quarters (73%) of residual exposure was estimated to occur outdoors. Based on observed levels of ITN use in the study sites, the population-wide mean personal protection provided by ITNs was 42%.
Discussion/Conclusions This study identified gaps in malaria prevention in Zanzibar with results directly applicable for improving ongoing programme activities. While overall biting risk was low, the most notable finding was that current levels of ITN use are estimated to prevent less than half of exposure to malaria vector bites. Variation in ITN use across sites and seasons suggests that additional gains could be made through targeted social and behaviour change interventions. However, even for ITN users, gaps in protection remain, with a majority of exposure to vector bites occurring outdoors before going to sleep. Supplemental interventions targeting outdoor exposure to malaria vectors, and groups that may be at increased risk of exposure to malaria vectors, should be explored.
Keywords
Malaria, residual transmission, outdoor transmission, human behavior, Zanzibar, Tanzania, human-vector contact, human-vector interaction, exposure
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CURRENT STATUS: Published
Version 2
Posted 29 May, 2020
Published
On 22 Jun, 2020
No community comments so far
Editor assigned
On 21 May, 2020
Editorial decision: Accept
On 21 May, 2020
Submission checks complete
On 20 May, 2020
Editor invited
On 20 May, 2020
No comments provided
Editorial decision: Minor Revision
On 28 Apr, 2020
Review #1 received
Received 31 Dec, 2019
Reviewer #1 agreed
On 13 Dec, 2019
Reviewers invited
Invitations sent on 21 Nov, 2019
Editor assigned
On 20 Nov, 2019
Submission checks complete
On 19 Nov, 2019
Editor invited
On 19 Nov, 2019
First submitted
On 13 Nov, 2019
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Subject Areas
Infectious Diseases
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This preprint is under consideration at Malaria Journal. A preprint is 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
Patterns of human exposure to malaria vectors in Zanzibar and implications for malaria elimination efforts
April Monroe
Johns Hopkins University
Corresponding Author
ORCiD: https://orcid.org/0000-0002-8959-6837
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
Version 2
Posted 29 May, 2020
Published
On 22 Jun, 2020
No community comments so far
Editor assigned
On 21 May, 2020
Editorial decision: Accept
On 21 May, 2020
Submission checks complete
On 20 May, 2020
Editor invited
On 20 May, 2020
No comments provided
Editorial decision: Minor Revision
On 28 Apr, 2020
Review #1 received
Received 31 Dec, 2019
Reviewer #1 agreed
On 13 Dec, 2019
Reviewers invited
Invitations sent on 21 Nov, 2019
Editor assigned
On 20 Nov, 2019
Submission checks complete
On 19 Nov, 2019
Editor invited
On 19 Nov, 2019
First submitted
On 13 Nov, 2019
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 version at Malaria Journal.
Background Zanzibar provides a good case study for malaria elimination. The islands have experienced a dramatic reduction in malaria burden since the introduction of effective vector control interventions and case management. Malaria prevalence has now been maintained below 1% for the past decade and the islands can feasibly aim for elimination.
Methods To better understand factors that may contribute to remaining low-level malaria transmission in Zanzibar, layered human behavioural and entomological research was conducted between December 2016 and December 2017 in 135 randomly selected households across six administrative wards. The study included: 1) household surveys, 2) structured household observations of nighttime activity and sleeping patterns, and 3) paired indoor and outdoor mosquito collections. Entomological and human behavioural data were integrated to provide weighted estimates of exposure to vector bites, accounting for proportions of people indoors or outdoors, and protected by insecticide-treated nets (ITNs) each hour of the night.
Results Overall, 92% of female Anopheles mosquitoes were caught in the rainy season compared to 8% in the dry season and 72% were caught outdoors compared to 28% indoors. For individual ITN users, ITNs prevented an estimated two-thirds (66%) of exposure to vector bites and nearly three quarters (73%) of residual exposure was estimated to occur outdoors. Based on observed levels of ITN use in the study sites, the population-wide mean personal protection provided by ITNs was 42%.
Discussion/Conclusions This study identified gaps in malaria prevention in Zanzibar with results directly applicable for improving ongoing programme activities. While overall biting risk was low, the most notable finding was that current levels of ITN use are estimated to prevent less than half of exposure to malaria vector bites. Variation in ITN use across sites and seasons suggests that additional gains could be made through targeted social and behaviour change interventions. However, even for ITN users, gaps in protection remain, with a majority of exposure to vector bites occurring outdoors before going to sleep. Supplemental interventions targeting outdoor exposure to malaria vectors, and groups that may be at increased risk of exposure to malaria vectors, should be explored.
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
Figure 7
Figure 8