Patterns of human exposure to malaria vectors in Zanzibar and implications for malaria elimination efforts

Abstract 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 behavioral and entomological research was conducted between December 2016 and December 2017 in 135 randomly selected households across six administrative wards selected based on high annual parasite incidence and receipt of indoor residual spraying (IRS). 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 behavioral 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: The percentage of study participants outdoors and away from home peaked in the early evening with a higher percentage of males observed away throughout the night compared to females. 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. Observed levels of ITN use were estimated to prevent an average of 42% of exposure to vector bites of all exposure that would otherwise occur. For ITN users, use of an ITN while asleep prevented an estimated two-thirds (66%) of exposure to vector bites and nearly three quarters (73%) of remaining exposure was estimated to occur outdoors. Discussion/Conclusions: This study identified gaps in malaria prevention in Zanzibar with results directly applicable for improving ongoing program 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 suggests that additional gains could be made through targeted social and behavior change interventions in sites with low levels of ITN use, with additional focus on increasing net use in the rainy season when biting risk is higher. 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. Interventions such as larval source management, which can reduce both indoor and outdoor-biting vector populations, could also be considered.

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Patterns of human exposure to malaria vectors in Zanzibar and implications for malaria elimination efforts

10.21203/rs.2.17609/v2 ◽

2020 ◽

Author(s):

April Monroe ◽

Dickson Msaky ◽

Samson Kiware ◽

Brian B. Tarimo ◽

Sarah Moore ◽

...

Keyword(s):

Malaria Elimination ◽

Malaria Prevention ◽

Outdoor Exposure ◽

Malaria Prevalence ◽

Malaria Vectors ◽

Insecticide Treated Nets ◽

Weighted Estimates ◽

Anopheles Mosquitoes ◽

Increased Risk ◽

Itn Use

Abstract 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.

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

10.21203/rs.2.19697/v1 ◽

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.

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Insecticide Susceptibility Profile of Malaria Vector Populations from the Coastal and Mainland Areas of Akwa Ibom State, Nigeria

Journal of Advances in Medicine and Medical Research ◽

10.9734/jammr/2019/v29i730099 ◽

2019 ◽

pp. 1-11

Author(s):

I. A. Atting ◽

N. D. Ekpo ◽

M. E. Akpan ◽

B. E. Bassey ◽

M. J. Asuquo ◽

...

Keyword(s):

Malaria Vector ◽

Scale Up ◽

Resistance Mechanism ◽

Indoor Residual Spraying ◽

Probit Model ◽

World Health ◽

Malaria Vectors ◽

Morphological Identification ◽

Insecticide Treated Nets ◽

Study Sites

Development of resistance by different malaria vector populations to insecticides has become a big threat to malaria vector elimination. This study evaluated the susceptibility of Anopheles mosquito populations in Akwa Ibom State, Nigeria to permethrin (0.75%), deltamethrin (0.5%), lambdacyhalothrin (0.5%), alphacypermethrin (0.75%), Dichlorodiphenyltrichloethane (DDT), propoxur, bendiocarb and pirimiphosmethylin in World Health Organization (WHO) test tubes following standard protocols. The mosquitoes were obtained as aquatic forms and reared under laboratory conditions to adults. The adults were subjected to WHO susceptibility bioassays following standard procedures. Malaria vectors across the study sites were resistant to permethrin, deltamethrin, lambdacyhalothrin and alphacypermethrin insecticides. Full susceptibility to propoxur and bendiocarb was recorded across the sites. Full susceptibility to pirimiphosmethyl was recorded in populations from three sites. Nevertheless, population of the malaria vectors collected from Oron was resistant to pirimiphosmethyl. KDT50 and KDT95 estimated for each insecticide using a log-time probit model revealed that knockdown was more rapid for deltamethrin, lambdacyhalothrin, alphacypermethrin, propoxur, bendiocarb and pirimiphosmethyl than for DDT and permethrin across the study sites. Morphological identification of all the mosquito samples used revealed that they were female Anopheles gambiae s.l. Sustained susceptibility of malaria vectors to pyrethriod is necessary for successful malaria control with insecticide treated nets and Indoor Residual Spraying (IRS). Emergence of focal points with insecticide resistance gives serious concern especially with the scale-up in distribution of pyrethriod treated nets to these areas. This may increase selection pressures due to overexposure. Further study to identify the exact resistance mechanism(s) of malaria vectors from these sites is recommended.

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Species Diversity and Entomological Inoculation Rate of Anophelines Mosquitoes in an Epidemic Prone Areas of Bure District, Northwestern Ethiopia

10.21203/rs.3.rs-103609/v1 ◽

2020 ◽

Author(s):

Tilahun Adugna Wassie ◽

Delensaw Yewhelew Gebru ◽

Emana Emana Getu (Prof.) Degaga

Keyword(s):

Species Diversity ◽

Disease Transmission ◽

Entomological Inoculation Rate ◽

Indoor Residual Spraying ◽

Northwest Ethiopia ◽

Malaria Vectors ◽

Insecticide Treated Nets ◽

Source Reduction ◽

Sporozoite Rate ◽

Control And Prevention

Abstract Background: Malaria is the leading health problem in Ethiopia. The country has been prevented malaria vectors mostly using long-lasting insecticide-treated nets, the application of indoor residual spraying chemicals, and source reductions. Before interventions, identifying the responsible malaria vector in disease transmission (sporozoite rate) is very vital; hence, the present study was designed to assess species diversity and entomological inoculation rate of Anopheles mosquito in Bure district, Northwest Ethiopia. Methods: Adult mosquitoes were collected from July 2015 to June 2016 using the center for disease control and prevention light traps, pyrethrum spray catches, and artificial pit shelters. Mosquitoes were morphologically identified. Following this, An. gambiae s.l was identified molecularly. Head-thorax sporozoite infectivity of the adult female Anopheles mosquitoes was assessed using enzyme-linked immunosorbent assays. Results: Morphologically, nine species of the genus Anopheles were identified in the three villages, composed of Anopheles demeilloni, An. arabiensis, An. funestus, An. coustani, An. squamosus, An. cinereus, An. pharoensis, An. rupicolus, and An. natalensis. Of these species, An. demeilloni was the most predominant, whereas An. cinereus, An. rupicolus and An. natalensis were the least representative species (p < 0.0001). Greater number of adult Anopheles mosquitoes were collected in Shnebekuma, non-irrigated villages than non- irrigated village (Workmidr) and irrigated village (Bukta) (p < 0.0001). The overall Plasmodium infective rate (P. falciparum and P. vivax) in the district was 0.31%. The overall annual sporozoite rate in non-irrigated villages (Shnebekuma and Workmidr) was 0.35%, whereas zero in irrigated village (Bukta). The overall estimated EIR of Anopheles mosquitoes was 5.7 infectious bites /person /year for both P. falciparum and P. vivax in the district. The annual EIR Anopheles species in non-irrigated villages was 5.65 ib/p/y, which was higher than irrigated village (0 ib/p/y). Conclusions: Both the primary (An. arabiensis) and secondary (An. funestus and An. pharoensis) malaria vectors of Ethiopia were identified in the three villages. Three of Anopheles species, An. arabiensis, An. funestus, and An. coustani were found to be infected only in irrigated villages. Source reduction and proper usage of long-lasting insecticide nets and indoor residual spraying could be implemented in the non- irrigated villages to cut the vector abundance and EIR.

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Anopheles gambiae s. l. larval control: An important method for malaria control

World Journal of Biology Pharmacy and Health Sciences ◽

10.30574/wjbphs.2021.6.3.0043 ◽

2021 ◽

Vol 6 (3) ◽

pp. 027-034

Author(s):

Nazaire Aïzoun

Keyword(s):

Anopheles Gambiae ◽

Malaria Control ◽

Malaria Elimination ◽

Rainy Season ◽

Enzyme Inhibitor ◽

Integrated Control ◽

Detoxification Enzymes ◽

Malaria Vectors ◽

Important Method ◽

Susceptibility Tests

The current study aimed to investigate on the control tools against larvae and adults of Anopheles gambiae s. l. and then explore the detoxification enzymes mechanisms conferring permethrin tolerance in Anopheles gambiae s. l. larvae in Benin. Larvae and pupae were collected from March to July and August to November 2018 during the rainy season in Bopa district in Mono department in south-western Benin, West Africa. Larval bioassays were performed on these collected Anopheles gambiae s. l. larvae using permethrin as larvicide and synergist piperonyl butoxide (PBO) as enzyme inhibitor or synergist. WHO susceptibility tests were also conducted on adult unfed female mosquitoes aged 3-5 days old with impregnated papers of permethrin (0.75%). The results showed that malaria elimination in Benin needs integrated control. Both larvae or pupae and adults malaria vectors must be controlled.

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Is outdoor-resting behaviour in malaria vectors consistent? Short report from northern Ghana.

10.21203/rs.3.rs-572080/v2 ◽

2021 ◽

Author(s):

Majidah Hamid-Adiamoh ◽

Davis Nwakanma ◽

Isaac Sr ◽

Alfred Amambua-Ngwa ◽

Yaw A. Afrane

Keyword(s):

Fluorescent Dyes ◽

Indoor Residual Spraying ◽

Blood Feeding ◽

Northern Ghana ◽

Malaria Vectors ◽

Short Report ◽

Insecticide Treated Nets ◽

Resting Behaviour ◽

Vector Population ◽

Outdoor Resting

Abstract Background Recent reports of a change in the resting behaviour of malaria vectors, from predominantly indoor resting to outdoor resting following blood feeding, have been attributed to selection pressure from use of vector control tools such as indoor residual spraying and long-lasting insecticide-treated nets. Recent studies have observed vectors resting predominantly outdoors in settings where anti-vector tools are extensively deployed. This present study examined if the outdoor resting behaviour in the vector population, is random or indicative of a consistent preference of one resting site over the other. Methods Mark-release-recapture (MRR) experiments were conducted with outdoor-resting Anopheles gambiae and An. funestus mosquitoes collected from pit shelters, animal houses and granaries in two villages in Northern Ghana during rainy and dry seasons. Mosquitoes were marked with fluorescent dyes and released indoors. The experiments were controlled with indoor-resting mosquitoes, which were marked and released outdoors. Species of all recaptured mosquitoes were identified and assessed for consistency in their resting behaviour. Results A total of 4,460 outdoor-resting mosquitoes comprising An. gambiae sensu lato (s.l.) (2,630, 59%) and An. funestus complex (1,830, 41%) were marked and released. Overall, 31 (0.7%) mosquitoes were recaptured mostly from outdoor location comprising 25 (81%) An. gambiae s.l. and 6 (19%) An. funestus complex. Only 3 (10%) of the recaptured mosquitoes were found resting indoors where they were released. The majority of the outdoor-recaptured mosquitoes were An. arabiensis (11, 39%), followed by An. coluzzii (7, 25%); whereas all indoor-recaptured mosquitoes were An. coluzzii. For the control experiment, 324 indoor-resting mosquitoes constituting 313 (97%) An. gambiae s.l. and 11 (3%) An. funestus complex were marked and released. However, none of these was recaptured neither indoors nor outdoors. More mosquitoes were significantly captured and recaptured during rainy season ( Z = 6.579, P < 0.0001). Conclusions The results obtained suggested the tendency for the mosquitoes to retain their outdoor-resting behaviour. Further investigations are required to ascertain if emerging preference for outdoor resting behaviour in malaria vector populations is consistent or a random occurrence.

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

10.21203/rs.3.rs-19762/v2 ◽

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.

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Evidence of pyrethroid resistance in Anopheles amharicus and Anopheles arabiensis from Arjo-Didessa irrigation scheme, Ethiopia

PLoS ONE ◽

10.1371/journal.pone.0261713 ◽

2022 ◽

Vol 17 (1) ◽

pp. e0261713

Author(s):

Assalif Demissew ◽

Abebe Animut ◽

Solomon Kibret ◽

Arega Tsegaye ◽

Dawit Hawaria ◽

...

Keyword(s):

Malaria Control ◽

Pyrethroid Resistance ◽

Management Strategies ◽

Resistance Management ◽

Indoor Residual Spraying ◽

Resistance Mechanisms ◽

Malaria Vectors ◽

Insecticide Treated Nets ◽

Irrigation Area ◽

Specific Pcr

Background Indoor residual spraying and insecticide-treated nets are among the key malaria control intervention tools. However, their efficacy is declining due to the development and spread of insecticide resistant vectors. In Ethiopia, several studies reported resistance of An. arabiensis to multiple insecticide classes. However, such data is scarce in irrigated areas of the country where insecticides, pesticides and herbicides are intensively used. Susceptibility of An. gambiae s.l. to existing and new insecticides and resistance mechanisms were assessed in Arjo-Didessa sugarcane plantation area, southwestern Ethiopia. Methods Adult An. gambiae s.l. reared from larval/pupal collections of Arjo-Didessa sugarcane irrigation area and its surrounding were tested for their susceptibility to selected insecticides. Randomly selected An. gambiae s.l. (dead and survived) samples were identified to species using species-specific polymerase chain reaction (PCR) and were further analyzed for the presence of knockdown resistance (kdr) alleles using allele-specific PCR. Results Among the 214 An. gambiae s.l. samples analyzed by PCR, 89% (n = 190) were An. amharicus and 9% (n = 20) were An. arabiensis. Mortality rates of the An. gambiae s.l. exposed to deltamethrin and alphacypermethrin were 85% and 86.8%, respectively. On the other hand, mortalities against pirmiphos-methyl, bendiocarb, propoxur and clothianidin were 100%, 99%, 100% and 100%, respectively. Of those sub-samples (An. amharicus and An. arabiensis) examined for presence of kdr gene, none of them were found to carry the L1014F (West African) allelic mutation. Conclusion Anopheles amharicus and An. arabiensis from Arjo-Didessa sugarcane irrigation area were resistant to pyrethroids which might be synergized by extensive use of agricultural chemicals. Occurrence of pyrethroid resistant malaria vectors could challenge the ongoing malaria control and elimination program in the area unless resistance management strategies are implemented. Given the resistance of An. amharicus to pyrethroids, its behavior and vectorial capacity should be further investigated.

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

10.21203/rs.2.19697/v2 ◽

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.

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Preferred resting surfaces of dominant malaria vectors inside different house types in rural south-eastern Tanzania

10.21203/rs.2.18018/v1 ◽

2019 ◽

Author(s):

Betwel John Msugupakulya ◽

Emmanuel W. Kaindoa ◽

Halfan S. Ngowo ◽

Japhet M. Kihonda ◽

Najat F. Kahamba ◽

...

Keyword(s):

Anopheles Funestus ◽

Indoor Residual Spraying ◽

Malaria Vectors ◽

Bed Nets ◽

Insecticide Treated Nets ◽

Rural South ◽

South Eastern ◽

Malaria Mosquitoes ◽

Common House ◽

Contact Insecticides

Abstract Background Malaria control in Africa relies extensively on indoor residual spraying (IRS) and insecticide-treated nets (ITNs). IRS typically targets mosquitoes resting on walls, and in few cases, roofs and ceilings, using contact insecticides. Unfortunately, little attention is paid to where malaria vectors actually rest indoors, and how such knowledge could be used to improve IRS. This study investigated preferred resting surfaces of two major malaria vectors, Anopheles funestus and Anopheles arabiensis , inside four common house types in rural south-eastern Tanzania.Methodology The assessment was done inside 80 houses including: 20 with thatched roofs and mud walls, 20 with thatched roofs and un-plastered brick walls, 20 with metal roofs and un-plastered brick walls, and 20 with metal roofs and plastered brick walls, across four villages. In each house, resting mosquitoes were sampled in mornings (6am-8am), evenings (6pm-8pm) and at night (11pm-12.00am) using Prokopack aspirators from multiple surfaces (walls, undersides of roofs, floors, furniture, utensils, clothing, curtains and bed nets).Results Overall, only 26% of An. funestus and 18% of An. arabiensis were found on walls. In grass-thatched houses, 33-55% of An. funestus and 43-50% of An. arabiensis rested under roofs, while in metal-roofed houses, only 16-20% of An. funestus and 8-30% of An. arabiensis rested under roofs. Considering all data together, approximately 40% of mosquitoes rested on surfaces not typically targeted by IRS, i.e. floors, furniture, utensils, clothing and bed nets. These proportions were particularly high in metal-roofed houses (47-53% of An. funestus ; 60-66% of An. arabiensis ).Conclusion While IRS typically uses contact insecticides to target adult mosquitoes on walls, and occasionally roofs and ceilings, significant proportions of vectors rest on surfaces not usually sprayed. This gap exceeds one-third of malaria mosquitoes in grass-thatched houses, and can reach two-thirds in metal-roofed houses. Where field operations exclude roofs during IRS, the gaps can be much greater. In conclusion, there is need for locally-obtained data on mosquito resting behaviours and how these influence the overall impact and costs of IRS. This study also emphasizes the need for alternative approaches, e.g. house screening, which broadly tackle mosquitoes beyond areas reachable by IRS and ITNs.

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