scholarly journals Evaluation of different deployment strategies for larviciding to control malaria: a simulation study

2021 ◽  
Vol 20 (1) ◽  
Author(s):  
Manuela Runge ◽  
Salum Mapua ◽  
Ismail Nambunga ◽  
Thomas A. Smith ◽  
Nakul Chitnis ◽  
...  
Keyword(s):  
Malaria Transmission ◽  
Critical Role ◽  
Indoor Residual Spraying ◽  
Malaria Prevalence ◽  
Transmission Model ◽  
Malaria Vectors ◽  
Relative Reduction ◽  
Insecticide Treated Nets ◽  
Host Seeking ◽  
The Impact

Abstract Background Larviciding against malaria vectors in Africa has been limited to indoor residual spraying and insecticide-treated nets, but is increasingly being considered by some countries as a complementary strategy. However, despite progress towards improved larvicides and new tools for mapping or treating mosquito-breeding sites, little is known about the optimal deployment strategies for larviciding in different transmission and seasonality settings. Methods A malaria transmission model, OpenMalaria, was used to simulate varying larviciding strategies and their impact on host-seeking mosquito densities, entomological inoculation rate (EIR) and malaria prevalence. Variations in coverage, duration, frequency, and timing of larviciding were simulated for three transmission intensities and four transmission seasonality profiles. Malaria transmission was assumed to follow rainfall with a lag of one month. Theoretical sub-Saharan African settings with Anopheles gambiae as the dominant vector were chosen to explore impact. Relative reduction compared to no larviciding was predicted for each indicator during the simulated larviciding period. Results Larviciding immediately reduced the predicted host-seeking mosquito densities and EIRs to a maximum that approached or exceeded the simulated coverage. Reduction in prevalence was delayed by approximately one month. The relative reduction in prevalence was up to four times higher at low than high transmission. Reducing larviciding frequency (i.e., from every 5 to 10 days) resulted in substantial loss in effectiveness (54, 45 and 53% loss of impact for host-seeking mosquito densities, EIR and prevalence, respectively). In seasonal settings the most effective timing of larviciding was during or at the beginning of the rainy season and least impactful during the dry season, assuming larviciding deployment for four months. Conclusion The results highlight the critical role of deployment strategies on the impact of larviciding. Overall, larviciding would be more effective in settings with low and seasonal transmission, and at the beginning and during the peak densities of the target species populations. For maximum impact, implementers should consider the practical ranges of coverage, duration, frequency, and timing of larviciding in their respective contexts. More operational data and improved calibration would enable models to become a practical tool to support malaria control programmes in developing larviciding strategies that account for the diversity of contexts.

scholarly journals Creating mosquito-free outdoor spaces using transfluthrin-treated chairs and ribbons

2019 ◽  
Author(s):  
John Paliga Masalu ◽  
Marceline Finda ◽  
Gerry F. Killeen ◽  
Halfan S. Ngowo ◽  
Polius G. Pinda ◽  
...  
Keyword(s):  
Anopheles Funestus ◽  
Indoor Residual Spraying ◽  
Malaria Vectors ◽  
Insecticide Treated Nets ◽  
Domestic Spaces ◽  
Host Seeking ◽  
Outdoor Spaces ◽  
Outdoor Biting ◽  
Outdoor Environments ◽  
Almost All

Abstract Background Residents of malaria-endemic communities spend several hours outdoors performing different activities, e.g. cooking, story-telling or eating, thereby exposing themselves to potentially-infectious mosquitoes. This compromises effectiveness of indoor interventions, notably long-lasting insecticide-treated nets (LLINs) and indoor residual spraying (IRS). This study characterized common peri-domestic spaces in rural south-eastern Tanzania, and assessed protective efficacies of hessian fabric mats and ribbons treated with the spatial repellent, transfluthrin and respectively fitted to chairs and outdoor kitchens, against mosquitoes.Methods Two hundred households were surveyed, and their most-used peri-domestic spaces physically characterized. Protective efficacies of locally-made transfluthrin-emanating chairs and hessian ribbons were tested in outdoor environments of eight households using volunteer-occupied exposure-free double net traps. CDC light traps were used to estimate host-seeking mosquito densities within open-structure outdoor kitchens. Field-collected Anopheles arabiensis and Anopheles funestus mosquitoes were exposed underneath the chairs to estimate 24h-mortality. Finally, WHO insecticide susceptibility tests were conducted on wild-caught Anopheles from the villages.Results Approximately half (52%) of houses had verandas. Aside from these verandas, most houses also had peri-domestic spaces where residents stayed most times (67% of houses with verandas and 94% of non-veranda houses). Two-thirds of these spaces were sited under trees, and only one third (34.4%) were built-up. The outdoor structures were usually makeshift kitchens having roofs and partial walls. Transfluthrin-treated chairs reduced outdoor-biting An. arabiensis densities by 70-76% while transfluthrin-treated hessian ribbons fitted to the outdoor kitchens caused 81% reduction in the general peri-domestic area. Almost all the field-collected An. arabiensis (99.4%) and An. funestus (100%) exposed under transfluthrin-treated chairs died. The An. arabiensis were susceptible to non-pyrethroids (pirimiphos methyl & bendiocarb) but resistant to pyrethroids commonly used on LLINs (deltamethrin & permethrin).Conclusion Most houses had actively-used peri-domestic outdoor spaces where exposure to mosquitoes occurred. The transfluthrin-treated chair and ribbons reduced outdoor-biting malaria vectors in these peri-domestic spaces, and also elicited significant mortality among pyrethroid-resistant field-caught malaria vectors. These two new prototype formats for transfluthrin emanators, if developed further, may constitute new options for complementing LLINs and IRS with outdoor protection against malaria and other mosquito-borne pathogens in areas where peri-domestic human activities are common.

scholarly journals Passive Outdoor Host Seeking Device (POHD): Designing and Evaluation against Outdoor Biting Malaria Vectors

2020 ◽  
Vol 2020 ◽  
pp. 1-15
Author(s):  
Stella T. Kessy ◽  
Ladslaus L. Mnyone ◽  
Bruno A. Nyundo ◽  
Issa N. Lyimo
Keyword(s):  
Carbon Dioxide ◽  
Malaria Transmission ◽  
Indoor Residual Spraying ◽  
Malaria Vectors ◽  
Natural Environments ◽  
Release Formulation ◽  
Experimental Hut ◽  
Host Seeking ◽  
Outdoor Biting ◽  
Residual Malaria Transmission

Odor-baited devices are increasingly needed to compliment long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS) for control of residual malaria transmission. However, the odor-baited devices developed so far are bulky, dependent on the source of electricity and carbon dioxide (CO2), and they are logistically unsuitable for scaling up in surveillance and control of malaria vectors. We designed a passive and portable outdoor host seeking device (POHD) and preliminarily evaluated suitable components against Anopheles arabiensis that maintains residual malaria transmission. Experiments were conducted using semifield reared An. arabiensis within the semifield system at Ifakara Health Institute (IHI) in southeastern Tanzania. These mosquitoes were exposed to Suna traps® baited with BG lures or source of light and augmented with carbon dioxide (CO2) in view of identifying best attractants necessary to improve attractiveness of designed POHD. Two Suna traps® were hanged at the corner but outside the experimental hut in a diagonal line and rotated between four corners to control for the effect of position and wind direction on mosquito catches. Furthermore, mosquitoes were also exposed to either a bendiocarb-treated or bendiocarb-untreated POHD baited with Mbita blend, Ifakara blend, and worn socks and augmented with warmth (i.e., 1.5 liter bottle of warm water) inside an experimental hut or a screened rectangular box. This study demonstrated that mosquitoes were more strongly attracted to Suna trap® baited with BG lures and CO2 relative to those traps baited with a source of light and CO2. The POHD baited with synthetic blends attracted and killed greater proportion of An. arabiensis compared with POHD baited with worn socks. Efficacy of the POHD was unaffected by source of warmth, and it was reduced by about 50% when the device was tested inside a screened rectangular box relative to closed experimental hut. Overall, this study demonstrates that the POHD baited with synthetic blends (Mbita and Ifakara blends) and bendiocarb can effectively attract and kill outdoor biting malaria vector species. Such POHD baited with synthetic blends may require the source of CO2 to enhance attractiveness to mosquitoes. Further trials are, therefore, ongoing to evaluate attractiveness of improved design of POHD baited with slow-release formulation of synthetic blends and sustainable source of CO2 to malaria vectors under semifield and natural environments.

scholarly journals Impact of indoor residual spraying on malaria transmission in the Moïssala health district, Chad

2019 ◽  
Author(s):  
Demba Kodindo Israël ◽  
Diomba Dobar Abel ◽  
Adoum Mahamat Oumar ◽  
Moundai Tchonfinet ◽  
Amen Nakebang Fadel ◽  
...  
Keyword(s):  
Malaria Transmission ◽  
Human Subjects ◽  
Indoor Residual Spraying ◽  
Common Species ◽  
Health District ◽  
Malaria Vectors ◽  
Eastern Zone ◽  
Short Period ◽  
One Year ◽  
The Impact

Abstract BackgroudMalaria is a major public health and development problem in Africa. In Chad in 2016, with 720 765 confirmed cases and 1 686 deaths, malaria is the main cause of consultations, hospitalizations and deaths in health facilities. A longitudinal entomological study was carried out from 07 to 24 December 2016 in the Moïssala health district. The objective of the study was to assess the impact of malaria transmission one year after two cycles of indoor residual spraying of 80% bendiocarb wettable powder (Ficam WP 80 W).MethodsTwo areas were defined for the study: the town of Dembo, located in the sprayed area, was chosen as the test town and Moïssala, located in the untreated area, was chosen as the control town. Two sampling methods were used: collection of resting endophilic fauna and direct capture of aggressive mosquitoes from human subjects. ResultsA total of 16 sessions of catches on human subjects totalling 32 man-nights were conducted and 160 rooms were sprayed per site. For 160 sprayed chambers per site, two anopheles were captured in Dembo compared to 547 in Moïssala. Three anophelian species have been morphologically identified. In Moïssala, An gambiae sl (An colluzzii : 96%, An gambiae : 4%), An funestus and An rufipes were captured at rest in the rooms and on human bait. In Dembo, the two anopheles, An colluzzii and An funestus were captured at rest in the rooms. On human bait as in endophilic fauna, An gambiae sp was the most common species in Moïssala. The aggressive anophelian density was zero in Dembo while it is 9 bites per man per night in Mosesala. Only Anopheles gambiae sp was found infected in aggressive wildlife. The sporozoite index of the aggressive fauna of An gambiae sp was 7.45%. Malaria transmission was estimated at 0.67 infected bites per man per night, or 244.55 infected bites per man per year. In endophilic fauna, An gambiae sp and An rufipes were the two species found infected in Moïssala with sporozoite indices of 6.70% (23/343) and 20% (2/10) respectively. However, in Dembo, neither of the two captured individuals was found infected.ConclusionsThe indoor residual spraying campaign in the eastern zone of the Moïssala health district has led to the collapse of the density and aggressiveness of malaria vectors. However, its evaluation over a short period of time is not sufficient to assess the impact of malaria transmission in this stable and highly endemic malaria zone.

scholarly journals Rapid reduction of malaria transmission following the introduction of indoor residual spraying in previously unsprayed districts: an observational analysis of Mopti Region, Mali, in 2017

2020 ◽  
Vol 19 (1) ◽  
Author(s):  
Joseph Wagman ◽  
Idrissa Cissé ◽  
Diakalkia Kone ◽  
Seydou Fomba ◽  
Erin Eckert ◽  
...  
Keyword(s):  
Malaria Transmission ◽  
Pyrethroid Resistance ◽  
Indoor Residual Spraying ◽  
Incidence Rates ◽  
Malaria Vectors ◽  
Malaria Control Programme ◽  
Difference In Differences ◽  
Peak Incidence ◽  
Significant Difference ◽  
The Impact

Abstract Background The National Malaria Control Programme (NMCP) of Mali has had recent success decreasing malaria transmission using 3rd generation indoor residual spraying (IRS) products in areas with pyrethroid resistance, primarily in Ségou and Koulikoro Regions. In 2015, national survey data showed that Mopti Region had the highest under 5-year-old (u5) malaria prevalence at 54%—nearly twice the national average—despite having high access to long-lasting insecticidal nets (LLINs) and seasonal malaria chemoprevention (SMC). Accordingly, in 2016 the NMCP and other stakeholders shifted IRS activities from Ségou to Mopti. Here, the results of a series of observational analyses utilizing routine malaria indicators to evaluate the impact of this switch are presented. Methods A set of retrospective, eco-observational time-series analyses were performed using monthly incidence rates of rapid diagnostic test (RDT)-confirmed malaria cases reported in the District Health Information System 2 (DHIS2) from January 2016 until February 2018. Comparisons of case incidence rates were made between health facility catchments from the same region that differed in IRS status (IRS vs. no-IRS) to describe the general impact of the 2016 and 2017 IRS campaigns, and a difference-in-differences approach comparing changes in incidence from year-to-year was used to describe the effect of suspending IRS operations in Ségou and introducing IRS operations in Mopti in 2017. Results Compared to communities with no IRS, cumulative case incidence rates in IRS communities were reduced 16% in Ségou Region during the 6 months following the 2016 campaign and 31% in Mopti Region during the 6 months following the 2017 campaign, likely averting a total of more than 22,000 cases of malaria that otherwise would have been expected during peak transmission months. Across all comparator health facilities (HFs) where there was no IRS in either year, peak malaria case incidence rates fell by an average of 22% (CI95 18–30%) from 2016 to 2017. At HFs in communities of Mopti where IRS was introduced in 2017, peak incidence fell by an average of 42% (CI95 31–63%) between these years, a significantly greater decrease (p = 0.040) almost double what was seen in the comparator HFCAs. The opposite effect was observed in Ségou Region, where peak incidence at those HFs where IRS was withdrawn after the 2016 campaign increased by an average of 106% (CI95 63–150%) from year to year, also a significant difference-in-differences compared to the comparator no-IRS HFs (p < 0.0001). Conclusion Annual IRS campaigns continue to make dramatic contributions to the seasonal reduction of malaria transmission in communities across central Mali, where IRS campaigns were timed in advance of peak seasonal transmission and utilized a micro-encapsulated product with an active ingredient that was of a different class than the one found on the LLINs used throughout the region and to which local malaria vectors were shown to be susceptible. Strategies to help mitigate the resurgence of malaria cases that can be expected should be prioritized whenever the suspension of IRS activities in a particular region is considered.

scholarly journals Anopheles funestus mosquitoes from rural south-eastern Tanzania may have stronger resistance to pyrethroids than the other malaria vector, Anopheles arabiensis

2020 ◽  
Author(s):  
Polius Gerazi Pinda ◽  
Claudia Eichenberger ◽  
Halfan S Ngowo ◽  
Dickson S Msaky ◽  
Said Abbasi ◽  
...  
Keyword(s):  
Malaria Transmission ◽  
Anopheles Arabiensis ◽  
Pyrethroid Resistance ◽  
Anopheles Funestus ◽  
Indoor Residual Spraying ◽  
The Other ◽  
Sub Saharan Africa ◽  
Malaria Vectors ◽  
Insecticide Treated Nets ◽  
South Eastern

Abstract 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 south-eastern Tanzania, pyrethroid-resistant Anopheles funestus are now implicated in > 80% of malaria infections, even in villages where the species occurs at lower densities than the other vector species, Anopheles arabiensis. This study compared the intensities of resistance between the two malaria vectors, so as to improve options for control. Methods: The study used WHO assays with 1×, 5× and 10× insecticide doses to assess levels of resistance, followed by synergist bioassays to understand possible mechanisms of the observed resistance phenotypes. The tests involved adult mosquitoes collected from villages across two districts in south-eastern Tanzania and identified using morphological and molecular approaches.Findings: At baseline doses (1×), both species were resistant to the two pyrethroids (permethrin and deltamethrin) but susceptible to the organophosphate (pirimiphos-methyl). An. funestus, but not An. arabiensis was also resistant to the carbamate (bendiocarb) at baseline doses. Both species were generally resistant to DDT, except An.arabiensis from one village. An. funestus showed strong resistance to pyrethroids, surviving the 5× and 10× doses except in one village. Pre-exposure to the synergist, piperonyl butoxide (PBO), enhanced the potency of pyrethroid 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 dominates malaria transmission, this study may suggest that the species also have much stronger resistance to pyrethroids than its counterpart, An. arabiensis and can survive more classes of insecticides, including carbamates. The pyrethroid resistance in both species appears to be mostly metabolic and may be temporarily addressed using synergists, e.g. PBO. These findings may explain the continued persistence and dominance of An. funestus despite widespread use of pyrethroid-treated LLINs, and inform new choices of interventions to tackle malaria transmission in such settings. These may include PBO-based LLINs or improved IRS with compounds to which the vectors are susceptible. Additional field validation of these indications will be necessary using age-synchronized mosquitoes.

scholarly journals Creating mosquito-free outdoor spaces using transfluthrin-treated chairs and ribbons

2020 ◽  
Author(s):  
John Paliga Masalu ◽  
Marceline Finda ◽  
Gerry F. Killeen ◽  
Halfan S. Ngowo ◽  
Polius G. Pinda ◽  
...  
Keyword(s):  
Anopheles Funestus ◽  
Indoor Residual Spraying ◽  
Malaria Vectors ◽  
Insecticide Treated Nets ◽  
Domestic Spaces ◽  
Host Seeking ◽  
Outdoor Spaces ◽  
Outdoor Biting ◽  
Outdoor Environments ◽  
Almost All

Abstract Background: Residents of malaria-endemic communities spend several hours outdoors performing different activities, e.g. cooking, story-telling or eating, thereby exposing themselves to potentially-infectious mosquitoes. These behaviors compromise effectiveness of indoor interventions, notably long-lasting insecticide-treated nets (LLINs) and indoor residual spraying (IRS). This study characterized common peri-domestic spaces in rural south-eastern Tanzania, and assessed protective efficacies of hessian fabric mats and ribbons treated with the spatial repellent, transfluthrin and respectively fitted to chairs and outdoor kitchens, against mosquitoes. Methods : Two hundred households were surveyed, and their most-used peri-domestic spaces physically characterized. Protective efficacies of locally-made transfluthrin-emanating chairs and hessian ribbons were tested in outdoor environments of 28 households in dry and wet seasons, using volunteer-occupied exposure-free double net traps. CDC light traps were used to estimate host-seeking mosquito densities within open-structure outdoor kitchens. Field-collected Anopheles arabiensis and Anopheles funestus mosquitoes were exposed underneath the chairs to estimate 24h-mortality. Finally, WHO insecticide susceptibility tests were conducted on wild-caught Anopheles from the villages. Results : Approximately half (52%) of houses had verandas. Aside from these verandas, most houses also had peri-domestic spaces where residents stayed most times (67% of houses with verandas and 94% of non-veranda houses). Two-thirds of these spaces were sited under trees, and one third (34.4%) were built-up. The outdoor structures were usually makeshift kitchens having roofs and partial walls. Transfluthrin-treated chairs reduced outdoor-biting An. arabiensis densities by 70-85%, while transfluthrin-treated hessian ribbons fitted to the outdoor kitchens caused 77-81% reduction in the general peri-domestic area. Almost all the field-collected An. arabiensis (99.4%) and An. funestus (100%) exposed under transfluthrin-treated chairs died. The An. arabiensis were susceptible to non-pyrethroids (pirimiphos methyl & bendiocarb) but resistant to pyrethroids commonly used on LLINs (deltamethrin & permethrin). Conclusion: Most houses had actively-used peri-domestic outdoor spaces where exposures to mosquitoes occur. Both the transfluthrin-treated chairs and ribbons reduced outdoor-biting malaria vectors in the peri-domestic spaces, and elicited significant mortality among pyrethroid-resistant field-caught malaria vectors. These two prototype formats, if developed further, may constitute new options for complementing LLINs and IRS with outdoor protection against malaria and other mosquito-borne diseases in areas with significant peri-domestic activities. Keywords : Peri-domestic spaces, transfluthrin-treated chairs, eave ribbons, transfluthrin, spatial repellents, outdoor-biting, malaria vectors, Ifakara Health Institute.

scholarly journals Bionomics and ecology of Anopheles merus along the East and Southern Africa coast

2021 ◽  
Vol 14 (1) ◽  
Author(s):  
Brian Bartilol ◽  
Irene Omedo ◽  
Charles Mbogo ◽  
Joseph Mwangangi ◽  
Martin K. Rono
Keyword(s):  
Malaria Transmission ◽  
Mosquito Species ◽  
Scale Up ◽  
Indoor Residual Spraying ◽  
Temporal Distribution ◽  
Malaria Vectors ◽  
Behavioural Plasticity ◽  
Insecticide Treated Nets ◽  
Resting Behaviour ◽  
Residual Malaria Transmission

AbstractMalaria transmission persists despite the scale-up of interventions such as long-lasting insecticide-treated nets (LLINs) and indoor residual spraying (IRS). Understanding the entomological drivers of transmission is key for the design of effective and sustainable tools to address the challenge. Recent research findings indicate a shift in vector populations from the notorious Anopheles gambiae (s.s.) as a dominant vector to other species as one of the factors contributing to the persistence of malaria transmission. However, there are gaps in the literature regarding the minor vector species which are increasingly taking a lead role in malaria transmission. Currently, minor malaria vectors have behavioural plasticity, which allows their evasion of vector control tools currently in use. To address this, we have reviewed the role of Anopheles merus, a saltwater mosquito species that is becoming an important vector of malaria transmission along the East and Southern African coast. We performed a literature review from PubMed and Google Scholar and reviewed over 50 publications relating to An. merus's bionomics, taxonomy, spatial-temporal distribution and role in malaria transmission. We found that An. merus is an important vector of malaria and that it contributes to residual malaria transmission because of its exophilic tendencies, insecticide resistance and densities that peak during the dry seasons as the freshwater mosquitoes decline. Spatial and temporal studies have also shown that this species has increased its geographical range, densities and vectorial capacity over time. In this review, we highlight the resting behaviour and breeding habitats of this mosquito, which could be targeted for surveillance studies and control interventions.

scholarly journals The dominant malaria vector, Anopheles funestus from rural south-eastern Tanzania, is more strongly resistant to insecticides than Anopheles arabiensis

2020 ◽  
Author(s):  
Polius Gerazi Pinda ◽  
Claudia Eichenberger ◽  
Halfan S Ngowo ◽  
Dickson S Msaky ◽  
Said Abbasi ◽  
...  
Keyword(s):  
Malaria Transmission ◽  
Pyrethroid Resistance ◽  
Mosquito Species ◽  
Anopheles Funestus ◽  
Indoor Residual Spraying ◽  
Sub Saharan Africa ◽  
Malaria Vectors ◽  
Insecticide Treated Nets ◽  
South Eastern ◽  
Sub Saharan

Abstract 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.

scholarly journals Evaluation of personal protection afforded by repellent-treated sandals against mosquito bites in south-eastern Tanzania.

2020 ◽  
Author(s):  
Peter Onyango Sangoro ◽  
Tegemeo Gavana ◽  
Marceline Finda ◽  
Winfrida Mponzi ◽  
Emmanuel Hape ◽  
...  
Keyword(s):  
Field Experiments ◽  
Mosquito Species ◽  
Indoor Residual Spraying ◽  
Field Tests ◽  
Malaria Vectors ◽  
Insecticide Treated Nets ◽  
Large Cage ◽  
Full Field ◽  
Targeted Interventions ◽  
The Impact

Abstract Background Outdoor and early evening mosquito biting needs to be addressed if malaria elimination is to be achieved. While indoor-targeted interventions such as insecticide-treated nets and indoor residual spraying remain essential, complementary approaches that tackle persisting outdoor transmission are urgently required to maximize the impact. Major malaria vectors principally bite human hosts around the feet and ankles. Consequently, this study investigated whether sandals treated with efficacious spatial repellents can protect against outdoor biting mosquitoes. Methodology Sandals affixed with hessian bands measuring 48cm 2 treated with 6 ml, 10 ml and 12 ml of transfluthrin were tested in large cage semi-field and full field experiments. Sandals affixed with hessian bands measuring 240cm 2 and treated with 10 ml and 12ml of transfluthrin were also tested semi field experiments. Human landing catches (HLC) were used to assess reduction in biting exposure by comparing proportions of mosquitoes landing on volunteers wearing treated and untreated sandals. Sandals were tested against insectary reared Anopheles arabiensis mosquitoes in semi-field experiments and against wild mosquito species in rural Tanzania. Results In semi-field tests, sandals fitted with hessian bands measuring 48cm 2 and treated with 12 ml, 10ml and 6ml transfluthrin reduced mosquito landings by 45.9%, (95% confidence interval (C.I.) = 28–59%), 61.1% (48%–71%), and 25.9% (9% - 40%) respectively compared to untreated sandals. Sandals fitted with hessian bands measuring 240cm 2 and treated with 12 ml and 10ml transfluthrin reduced mosquito landings by 59% (43 - 71%) and 64% (48 - 74%) respectively. In field experiments, sandals fitted with hessian bands measuring 48cm 2 and treated with 12 ml transfluthrin reduced mosquito landings by 70% (60% - 76%) against Anopheles gambiae s.l and 66.0% (59% - 71%) against all mosquito species combined. Conclusion Transfluthrin-treated sandals conferred significant protection against mosquito bites in semi-field and field settings. Further evaluation is recommended for this tool as a potential complimentary intervention against malaria. This intervention could be particularly useful for protecting against outdoor exposure to mosquito bites. Additional studies are necessary to optimize treatment techniques and substrates, establish safety profiles and determine epidemiological impact in different settings.

scholarly journals Evaluation of personal protection afforded by repellent-treated sandals against mosquito bites in south-eastern Tanzania.

2020 ◽  
Author(s):  
Peter Onyango Sangoro ◽  
Tegemeo Gavana ◽  
Marceline Finda ◽  
Winfrida Mponzi ◽  
Emmanuel Hape ◽  
...  
Keyword(s):  
Field Experiments ◽  
Mosquito Species ◽  
Indoor Residual Spraying ◽  
Field Tests ◽  
Malaria Vectors ◽  
Insecticide Treated Nets ◽  
Large Cage ◽  
Full Field ◽  
Targeted Interventions ◽  
The Impact

Abstract Background Outdoor and early evening mosquito biting needs to be addressed if malaria elimination is to be achieved. While indoor-targeted interventions such as insecticide-treated nets and indoor residual spraying remain essential, complementary approaches that tackle persisting outdoor transmission are urgently required to maximize the impact. Major malaria vectors principally bite human hosts around the feet and ankles. Consequently, this study investigated whether sandals treated with efficacious spatial repellents can protect against outdoor biting mosquitoes. Methodology Sandals affixed with hessian bands measuring 48cm 2 treated with 6 ml, 10 ml and 12 ml of transfluthrin were tested in large cage semi-field and full field experiments. Sandals affixed with hessian bands measuring 240cm 2 and treated with 10 ml and 12ml of transfluthrin were also tested semi field experiments. Human landing catches (HLC) were used to assess reduction in biting exposure by comparing proportions of mosquitoes landing on volunteers wearing treated and untreated sandals. Sandals were tested against insectary reared Anopheles arabiensis mosquitoes in semi-field experiments and against wild mosquito species in rural Tanzania. Results In semi-field tests, sandals fitted with hessian bands measuring 48cm 2 and treated with 12 ml, 10ml and 6ml transfluthrin reduced mosquito landings by 45.9%, (95% confidence interval (C.I.) = 28–59%), 61.1% (48%–71%), and 25.9% (9% - 40%) respectively compared to untreated sandals. Sandals fitted with hessian bands measuring 240cm 2 and treated with 12 ml and 10ml transfluthrin reduced mosquito landings by 59% (43 - 71%) and 64% (48 - 74%) respectively. In field experiments, sandals fitted with hessian bands measuring 48cm 2 and treated with 12 ml transfluthrin reduced mosquito landings by 70% (60% - 76%) against Anopheles gambiae s.l and 66.0% (59% - 71%) against all mosquito species combined. Conclusion Transfluthrin-treated sandals conferred significant protection against mosquito bites in semi-field and field settings. Further evaluation is recommended for this tool as a potential complimentary intervention against malaria. This intervention could be particularly useful for protecting against outdoor exposure to mosquito bites. Additional studies are necessary to optimize treatment techniques and substrates, establish safety profiles and determine epidemiological impact in different settings.

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