Modelling the impact of larviciding on the population dynamics and biting rates of Simulium damnosum s.l.: implications for vector control as a complementary strategy for onchocerciasis elimination in Africa
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Supporting information
Published version
Author(s)
Type
Journal Article
Abstract
Background:
In 2012, the World Health Organization set goals for the elimination of
onchocerciasis transmission by 2020 in selected African countries. Epidemiological data and
mathematical modelling have indicated that elimination may not be achieved with
annual
ivermectin distribution in all endemic foci. Complementary and alternative treatment strategies
(ATS), including vector control, will be necessary. Implementation of vector control will require
that the ecology and population dynamics of
Simulium
da
mnosum
sensu lato
be carefully
considered.
Methods:
We adapted our previous SIMuliid POPulation dynamics (SIMPOP) model to explore
the impact of larvicidal insecticides on
S.
damnosum
s.l
.
biting rates in different ecological
contexts and to identify how
frequently and for how long vector control should be continued to
sustain substantive reductions in vector biting. SIMPOP was fitted to data from large
-
scale aerial
larviciding trials in savannah sites (Ghana) and small
-
scale ground larviciding trials in f
orest
areas (Cameroon). The model was validated against independent data from Burkina Faso/Côte
d’Ivoire (savannah) and Bioko (forest). Scenario analysis explored the effects of ecological and
programmatic factors such as pre
-
control daily biting rate (
DBR
) and larviciding scheme design
on reductions and resurgences in biting rates.
Results:
The estimated efficacy of large
-
scale aerial larviciding in the savannah was greater than
that of ground
-
based larviciding in the forest. Small changes in larvicidal ef
ficacy can have large
impacts on intervention success. At 93% larvicidal efficacy (a realistic value based on field
trials), 10 consecutive weekly larvicidal treatments would reduce
DBR
s by 9
6
% (e.g. from 400
to
16
bites/person/day
).
At 70% efficacy, and f
or 10 weekly applications, the
DBR
would
decrease by
6
7% (e.g. from 400 to
132
bites/person/day). Larviciding is more likely to succeed
in areas with lower water temperatures and where blackfly species have longer gonotrophic
cycles.
Conclusions:
Focal
vector control can reduce vector biting rates in settings where a high
larvicidal efficacy can be achieved and an appropriate duration and frequency of larviciding can
be ensured. Future work linking SIMPOP with onchocerciasis transmission models will perm
it
evaluation of the impact of combined anti
-
vectorial and anti
-
parasitic interventions on
accelerating elimination of the disease.
In 2012, the World Health Organization set goals for the elimination of
onchocerciasis transmission by 2020 in selected African countries. Epidemiological data and
mathematical modelling have indicated that elimination may not be achieved with
annual
ivermectin distribution in all endemic foci. Complementary and alternative treatment strategies
(ATS), including vector control, will be necessary. Implementation of vector control will require
that the ecology and population dynamics of
Simulium
da
mnosum
sensu lato
be carefully
considered.
Methods:
We adapted our previous SIMuliid POPulation dynamics (SIMPOP) model to explore
the impact of larvicidal insecticides on
S.
damnosum
s.l
.
biting rates in different ecological
contexts and to identify how
frequently and for how long vector control should be continued to
sustain substantive reductions in vector biting. SIMPOP was fitted to data from large
-
scale aerial
larviciding trials in savannah sites (Ghana) and small
-
scale ground larviciding trials in f
orest
areas (Cameroon). The model was validated against independent data from Burkina Faso/Côte
d’Ivoire (savannah) and Bioko (forest). Scenario analysis explored the effects of ecological and
programmatic factors such as pre
-
control daily biting rate (
DBR
) and larviciding scheme design
on reductions and resurgences in biting rates.
Results:
The estimated efficacy of large
-
scale aerial larviciding in the savannah was greater than
that of ground
-
based larviciding in the forest. Small changes in larvicidal ef
ficacy can have large
impacts on intervention success. At 93% larvicidal efficacy (a realistic value based on field
trials), 10 consecutive weekly larvicidal treatments would reduce
DBR
s by 9
6
% (e.g. from 400
to
16
bites/person/day
).
At 70% efficacy, and f
or 10 weekly applications, the
DBR
would
decrease by
6
7% (e.g. from 400 to
132
bites/person/day). Larviciding is more likely to succeed
in areas with lower water temperatures and where blackfly species have longer gonotrophic
cycles.
Conclusions:
Focal
vector control can reduce vector biting rates in settings where a high
larvicidal efficacy can be achieved and an appropriate duration and frequency of larviciding can
be ensured. Future work linking SIMPOP with onchocerciasis transmission models will perm
it
evaluation of the impact of combined anti
-
vectorial and anti
-
parasitic interventions on
accelerating elimination of the disease.
Date Issued
2018-05-29
Date Acceptance
2018-04-23
Citation
Parasites & Vectors, 2018, 11, pp.1-16
ISSN
1756-3305
Publisher
BioMed Central
Start Page
1
End Page
16
Journal / Book Title
Parasites & Vectors
Volume
11
Copyright Statement
© The Author(s). 2018 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0
International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and
reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to
the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver
(http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and
reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to
the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver
(http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
Sponsor
Wellcome Trust
Wellcome Trust
The Royal Society
The Task Force for Global Health
Wellcome Trust
Medical Research Council (MRC)
Medical Research Council (MRC)
Identifier
https://parasitesandvectors.biomedcentral.com/articles/10.1186/s13071-018-2864-y
Grant Number
085133/Z/08/Z
092677/Z/10/Z
AA90078
MA4501180169
109310/Z/15/Z
MR/K010174/1B
MR/R015600/1
Subjects
Science & Technology
Life Sciences & Biomedicine
Parasitology
Tropical Medicine
Onchocerciasis
Vector control
Vector ecology
Mathematical modelling
Population dynamics
Alternative treatment strategy
Elimination
Simulium damnosum (s.l.)
Africa
NEGLECTED TROPICAL DISEASES
CONTROL PROGRAM AREA
IVERMECTIN TREATMENT
RIVER-BLINDNESS
ECONOMIC-EVALUATION
WINDBORNE VECTORS
MASS TREATMENT
ENDEMIC AREAS
WEST-AFRICA
BIOKO FORM
Africa
Alternative treatment strategy
Elimination
Mathematical modelling
Onchocerciasis
Population dynamics
Simulium damnosum (s.l.)
Vector control
Vector ecology
Animals
Burkina Faso
Cameroon
Cote d'Ivoire
Disease Eradication
Ghana
Humans
Insect Bites and Stings
Insect Control
Insect Vectors
Insecticides
Ivermectin
Models, Theoretical
Onchocerciasis
Population Dynamics
Simuliidae
Animals
Humans
Simuliidae
Onchocerciasis
Insect Bites and Stings
Ivermectin
Insecticides
Insect Vectors
Population Dynamics
Insect Control
Models, Theoretical
Cameroon
Burkina Faso
Cote d'Ivoire
Ghana
Disease Eradication
Mycology & Parasitology
1108 Medical Microbiology
1117 Public Health and Health Services
Tropical Medicine
Publication Status
Published
Article Number
316
Date Publish Online
2018-05-29