Anopheles arabiensis and Anopheles funestus s.s. biting pattern in Dielmo, an area of low level exposure to malaria vectors.

Abstract Background In Dielmo, Senegal, the widespread use of long-lasting insecticidal nets has decreased both the incidence of malaria and the density of the Anopheles population. However, persistent low-level malaria transmission may hamper efforts to eliminate the disease. Therefore, continuous monitoring of the vector population is needed in order to improve knowledge of Anopheles biting behaviour and to readjust control interventions.Methods In 2015, Anopheles were collected every month for a whole year and each specimen was identified using morphological and molecular techniques. The biting pattern of each species was analysed according to night (7pm–7am) and morning (7am–11am) periods, the place of biting and the season. The ELISA CSP technique was used to assess the Plasmodium falciparum sporozoite rate to evaluate the entomological inoculation rate (EIR).Results Anopheles arabiensis and Anopheles funestus sensu stricto were found to be the main vectors biting humans. Overall, the biting rate was low, at 3.84bites per night (bpn) and 1.27 bites per morning (bpm), respectively (IRR =3.04, CI = [1.84-5.00], p<0.001). The EIR was 2.51 and 5.03 infectious bites per year during the night and morning, respectively. During the night, the An. arabiensis and An. funestus biting rate was 1.81 bpn and 1.71 bpn, respectively (IRR=0.95, CI= [0.46-1.92], p=0.88). During the morning, their density decreased to 0.51 bpm and 0.73 bpm for An. arabiensis and An. funestus, respectively (IRR=1.47, CI= [0.58-3.71], p=0.41). During the night and the morning, no specific trend of indoor or outdoor biting was observed in the dry and rainy season for both vectors. Conclusion This study highlighted low level Anopheles nocturnal and diurnal biting and the associated risk of malaria transmission. It showed also the influence of the season on the indoor and outdoor biting pattern, indicating that the human population could be exposed all year round to a low level of Anopheles bites. Control programmes should increase awareness of the use of bed nets throughout the year and promote the development and implementation of complimentary tools to target Anopheles biting shortly after dawn when people are still indoors.

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Entomological determinants of malaria transmission in Kayin state, Eastern Myanmar: A 24-month longitudinal study in four villages

Wellcome Open Research ◽

10.12688/wellcomeopenres.14761.3 ◽

2019 ◽

Vol 3 ◽

pp. 109

Author(s):

Victor Chaumeau ◽

Bénédicte Fustec ◽

Saw Nay Hsel ◽

Céline Montazeau ◽

Saw Naw Nyo ◽

...

Keyword(s):

Malaria Transmission ◽

Infection Rate ◽

Malaria Vectors ◽

Bed Nets ◽

Biting Rate ◽

Multiple Species ◽

Few Data ◽

Greater Mekong Subregion ◽

Very High ◽

Human Biting Rate

Background: The Thailand-Myanmar borderland is an area endemic for malaria where transmission is low, seasonal and unstable. The epidemiology has been described but there is relatively few data on the entomological determinants of malaria transmission. Methods: Entomological investigations were conducted during 24 months in four villages located in Kayin state, on the Myanmar side of the Thailand-Myanmar border. Anopheles mosquitoes were identified by morphology, and molecular assays were used in order to discriminate between closely related sibling species of malaria vectors. Plasmodium infection rate was determined using quantitative real-time PCR. Results: The diversity of Anopheles mosquitoes was very high and multiple species were identified as malaria vectors. The intensity of human-vector contact (mean human-biting rate= 369 bites/person/month) compensates for the low infection rate in naturally infected populations of malaria vectors (mean sporozoite index= 0.04 and 0.17 % for P. falciparum and P. vivax respectively), yielding intermediary level of transmission intensity (mean entomological inoculation rate= 0.13 and 0.64 infective bites/person/month for P. falciparum and P. vivax, respectively). Only 36% of the infected mosquitoes were collected indoors between 09:00 pm and 05:00 am, suggesting that mosquito bed-nets would fail to prevent most of the infective bites in the study area. Conclusion: This study provided a unique opportunity to describe the entomology of malaria in low transmission settings of Southeast Asia. Our data are important in the context of malaria elimination in the Greater Mekong Subregion.

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Entomological determinants of malaria transmission in Kayin state, Eastern Myanmar: A 24-month longitudinal study in four villages

Wellcome Open Research ◽

10.12688/wellcomeopenres.14761.1 ◽

2018 ◽

Vol 3 ◽

pp. 109 ◽

Cited By ~ 6

Author(s):

Victor Chaumeau ◽

Bénédicte Fustec ◽

Saw Nay Hsel ◽

Céline Montazeau ◽

Saw Naw Nyo ◽

...

Keyword(s):

Malaria Transmission ◽

Infection Rate ◽

Malaria Elimination ◽

Malaria Vectors ◽

Bed Nets ◽

Biting Rate ◽

Multiple Species ◽

Few Data ◽

Greater Mekong Subregion ◽

Human Biting Rate

Background: The Thailand-Myanmar borderland is an area endemic for malaria where transmission is low, seasonal and unstable. The epidemiology has been described but there is relatively few data on the entomological determinants of malaria transmission. Methods: As part of a pilot study on Targeted Malaria Elimination, entomological investigations were conducted during 24 months in four villages located in Kayin state, Myanmar. Anopheles mosquitoes were identified by morphology, and molecular assays were used in order to discriminate between closely related sibling species of malaria vectors. Plasmodium infection rate was determined using quantitative real-time PCR. Results: The biodiversity of Anopheles entomo-fauna was very high and multiple species were identified as malaria vectors. The intensity of human-vector contact (mean human-biting rate= 369 bites/person/month) compensates for the low infection rate in naturally infected populations of malaria vectors (mean sporozoite index= 0.4 and 1.7 /1,000 mosquitoes for P. falciparum and P. vivax respectively), yielding intermediary level of transmission intensity (mean entomological inoculation rate= 0.13 and 0.64 infective bites/person/month for P. falciparum and P. vivax, respectively). We estimated that 65% of the potential infective bites are not prevented by mosquito bed nets because of outdoor and early biters. Conclusion: This study provided a unique opportunity to describe the entomology of malaria in low transmission settings of Southeast Asia. Our data are important in the context of malaria elimination in the Greater Mekong Subregion.

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Entomological determinants of malaria transmission in Kayin state, Eastern Myanmar: A 24-month longitudinal study in four villages

Wellcome Open Research ◽

10.12688/wellcomeopenres.14761.2 ◽

2019 ◽

Vol 3 ◽

pp. 109

Author(s):

Victor Chaumeau ◽

Bénédicte Fustec ◽

Saw Nay Hsel ◽

Céline Montazeau ◽

Saw Naw Nyo ◽

...

Keyword(s):

Malaria Transmission ◽

Infection Rate ◽

Malaria Vectors ◽

Bed Nets ◽

Biting Rate ◽

Multiple Species ◽

Few Data ◽

Greater Mekong Subregion ◽

Very High ◽

Human Biting Rate

Background: The Thailand-Myanmar borderland is an area endemic for malaria where transmission is low, seasonal and unstable. The epidemiology has been described but there is relatively few data on the entomological determinants of malaria transmission. Methods: Entomological investigations were conducted during 24 months in four villages located in Kayin state, on the Myanmar side of the Thailand-Myanmar border. Anopheles mosquitoes were identified by morphology, and molecular assays were used in order to discriminate between closely related sibling species of malaria vectors. Plasmodium infection rate was determined using quantitative real-time PCR. Results: The diversity of Anopheles mosquitoes was very high and multiple species were identified as malaria vectors. The intensity of human-vector contact (mean human-biting rate= 369 bites/person/month) compensates for the low infection rate in naturally infected populations of malaria vectors (mean sporozoite index= 0.04 and 0.17 % for P. falciparum and P. vivax respectively), yielding intermediary level of transmission intensity (mean entomological inoculation rate= 0.13 and 0.64 infective bites/person/month for P. falciparum and P. vivax, respectively). Only 36% of the infected mosquitoes were collected indoors between 09:00 pm and 05:00 am, suggesting that mosquito bed-nets would fail to prevent most of the infective bites in the study area. Conclusion: This study provided a unique opportunity to describe the entomology of malaria in low transmission settings of Southeast Asia. Our data are important in the context of malaria elimination in the Greater Mekong Subregion.

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Entomological determinants of malaria transmission in Kayin state, Eastern Myanmar: A 24-month longitudinal study in four villages

Wellcome Open Research ◽

10.12688/wellcomeopenres.14761.4 ◽

2019 ◽

Vol 3 ◽

pp. 109 ◽

Cited By ~ 4

Author(s):

Victor Chaumeau ◽

Bénédicte Fustec ◽

Saw Nay Hsel ◽

Céline Montazeau ◽

Saw Naw Nyo ◽

...

Keyword(s):

Malaria Transmission ◽

Infection Rate ◽

Malaria Vectors ◽

Bed Nets ◽

Biting Rate ◽

Multiple Species ◽

Few Data ◽

Greater Mekong Subregion ◽

Very High ◽

Human Biting Rate

Background: The Thailand-Myanmar borderland is an area endemic for malaria where transmission is low, seasonal and unstable. The epidemiology has been described but there is relatively few data on the entomological determinants of malaria transmission. Methods: Entomological investigations were conducted during 24 months in four villages located in Kayin state, on the Myanmar side of the Thailand-Myanmar border. Anopheles mosquitoes were identified by morphology, and molecular assays were used in order to discriminate between closely related sibling species of malaria vectors. Plasmodium infection rate was determined using quantitative real-time PCR. Results: The diversity of Anopheles mosquitoes was very high and multiple species were identified as malaria vectors. The intensity of human-vector contact (mean human-biting rate= 369 bites/person/month) compensates for the low infection rate in naturally infected populations of malaria vectors (mean sporozoite index= 0.04 and 0.17 % for P. falciparum and P. vivax respectively), yielding intermediary level of transmission intensity (mean entomological inoculation rate= 0.13 and 0.64 infective bites/person/month for P. falciparum and P. vivax, respectively). Only 36% of the infected mosquitoes were collected indoors between 09:00 pm and 05:00 am, suggesting that mosquito bed-nets would fail to prevent most of the infective bites in the study area. Conclusion: This study provided a unique opportunity to describe the entomology of malaria in low transmission settings of Southeast Asia. Our data are important in the context of malaria elimination in the Greater Mekong Subregion.

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Variations in household microclimate affect outdoor-biting behaviour of malaria vectors

Wellcome Open Research ◽

10.12688/wellcomeopenres.12928.1 ◽

2017 ◽

Vol 2 ◽

pp. 102 ◽

Cited By ~ 22

Author(s):

Halfan S. Ngowo ◽

Emmanuel Wilson Kaindoa ◽

Jason Matthiopoulos ◽

Heather M. Ferguson ◽

Fredros O. Okumu

Keyword(s):

Mixed Models ◽

Anopheles Funestus ◽

Malaria Vectors ◽

Mosquito Vector ◽

Relative Temperature ◽

Mosquito Abundance ◽

Outdoor Biting ◽

Microclimatic Conditions ◽

The Impact ◽

Biting Behaviour

Background: Mosquito behaviours including the degree to which they bite inside houses or outside is a crucial determinant of human exposure to malaria. Whilst seasonality in mosquito vector abundance is well documented, much less is known about the impact of climate on mosquito behaviour. We investigated how variations in household microclimate affect outdoor-biting by malaria vectors, Anopheles arabiensis and Anopheles funestus. Methods: Mosquitoes were sampled indoors and outdoors weekly using human landing catches at eight households in four villages in south-eastern Tanzania, resulting in 616 trap-nights over 12 months. Daily temperature, relative humidity and rainfall were recorded. Generalized additive mixed models (GAMMs) were used to test associations between mosquito abundance and the microclimatic conditions. Generalized linear mixed models (GLMMs) were used to investigate the influence of microclimatic conditions on the tendency of vectors to bite outdoors (proportion of outdoor biting). Results: An. arabiensis abundance peaked during high rainfall months (February-May), whilst An. funestus density remained stable into the dry season (May-August). Across the range of observed household temperatures, a rise of 1ºC marginally increased nightly An. arabiensis abundance (~11%), but more prominently increased An. funestus abundance (~66%). The abundance of An. arabiensis and An. funestus showed strong positive associations with time-lagged rainfall (2-3 and 3-4 weeks before sampling). The degree of outdoor biting in An. arabiensis was significantly associated with the relative temperature difference between indoor and outdoor environments, with exophily increasing as temperature inside houses became relatively warmer. The exophily of An. funestus did not vary with temperature differences. Conclusions: This study demonstrates that malaria vector An. arabiensis shifts the location of its biting from indoors to outdoors in association with relative differences in microclimatic conditions. These environmental impacts could give rise to seasonal variation in mosquito biting behaviour and degree of protection provided by indoor-based vector control strategies.

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Insights into factors sustaining persistence of high malaria transmission in forested areas of sub-Saharan Africa: the case of Mvoua, South Cameroon

Parasites & Vectors ◽

10.1186/s13071-020-04525-0 ◽

2021 ◽

Vol 14 (1) ◽

Author(s):

Dominique Mieguim Ngninpogni ◽

Cyrille Ndo ◽

Patrick Ntonga Akono ◽

Anicet Nguemo ◽

Amine Nguepi ◽

...

Keyword(s):

Anopheles Gambiae ◽

Malaria Transmission ◽

Anopheles Funestus ◽

Mortality Rates ◽

Molecular Techniques ◽

Sub Saharan Africa ◽

World Health ◽

Enzyme Linked Immunosorbent Assay ◽

Pyrethroid Insecticides ◽

Kisumu Strain

Abstract Background In Mvoua, a village situated in a forested area of Cameroon, recent studies have reported high prevalence of Plasmodium falciparum infection among the population. In order to understand factors that can sustain such a high malaria transmission, we investigated the biology of Anopheles vectors and its susceptibility to insecticides, as well as long-lasting insecticidal net (LLIN) coverage, use and bio-efficacy. Methods A longitudinal entomological survey was conducted from July 2018 to April 2019. Adult mosquitoes were collected using the human landing catch (HLC) method and identified using morphological and molecular techniques. Anopheles gambiae (s.l.) larvae were sampled from several stagnant water pools throughout the village and reared to generate F1 adults. The presence of P. falciparum circumsporozoite antigen was detected in the heads and thoraces of mosquitoes collected as adults using an enzyme-linked immunosorbent assay. The insecticide susceptibility status of the local An. gambiae (s.l.) F1 population to the pyrethroid insecticides deltamethrin 0.5% and permethrin 0.75% was determined using World Health Organization-tube bioassays, while the frequency of the knockdown resistance (kdr) mutation was determined by PCR. Coverage, use and physical integrity of LLINs were assessed in households, then cone assays were used to test for their bio-efficacy on both the reference insecticide-susceptible Kisumu strain and on field F1 An. gambiae (s.l.) Results In total, 110 Anopheles mosquitoes were collected, of which 59.1% were identified as Anopheles funestus (s.l.), 38.18% as An. gambiae (s.l.) and 2.72% as An. ziemanii. Anopheles funestus was the most abundant species except in the long rainy season, when An. gambiae (s.l.) predominated (65.8%). In the dry seasons, vectors were principally endophagous (76% of those collected indoors) while they tended to be exophagous (66% of those collected outdoors) in rainy seasons. High Plasmodium infection was observed in An. gambiae (s.l.) and An. funestus, with a circumsporozoitic rate of 14.29 and 10.77%, respectively. Anopheles gambiae (s.l.) was highly resistant to pyrethroid insecticides (mortality rates: 32% for permethrin and 5% for deltamethrin) and harbored the kdr-L1014F mutation at a high frequency (89.74%). Of the 80 households surveyed, only 47.69% had achieved universal coverage with LLNs. Around 70% of the LLINs sampled were in poor physical condition, with a proportionate hole index > 300. Of the ten LLNs tested, eight were effective against the An. gambiae reference insecticide-susceptible Kisumu strain, showing mortality rate of > 80%, while none of these LLINs were efficient against local An. gamabie (s.l.) populations (mortality rates < 11.5%). Conclusion A combination of elevated P. falciparum infection in Anopheles vector populations, insufficient coverage and loss of effectiveness of LLINs due to physical degradation, as well as high resistance to pyrethroid insecticides is responsible for the persistence of high malaria transmission in forested rural area of Mvoua, Cameroon.

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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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Anopheles arabiensis and Anopheles funestus biting patterns in Dielmo, an area of low level exposure to malaria vectors

Malaria Journal ◽

10.1186/s12936-020-03302-9 ◽

2020 ◽

Vol 19 (1) ◽

Cited By ~ 1

Author(s):

Souleymane Doucoure ◽

Omar Thiaw ◽

Amélé N. Wotodjo ◽

Charles Bouganali ◽

Nafisatou Diagne ◽

...

Keyword(s):

Anopheles Arabiensis ◽

Anopheles Funestus ◽

Malaria Vectors ◽

Low Level

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An Experimental Hut Evaluation of PBO-Based and Pyrethroid-Only Nets against the Malaria Vector Anopheles funestus Reveals a Loss of Bed Nets Efficacy Associated with GSTe2 Metabolic Resistance

Genes ◽

10.3390/genes11020143 ◽

2020 ◽

Vol 11 (2) ◽

pp. 143 ◽

Cited By ~ 5

Author(s):

Benjamin D. Menze ◽

Mersimine F. Kouamo ◽

Murielle J. Wondji ◽

Williams Tchapga ◽

Micareme Tchoupo ◽

...

Keyword(s):

Anopheles Funestus ◽

Blood Feeding ◽

Malaria Vectors ◽

Bed Nets ◽

Glutathione S Transferase ◽

Metabolic Resistance ◽

Experimental Hut ◽

The Impact ◽

Long Lasting Insecticidal Nets ◽

Permanet 3.0

Growing insecticide resistance in malaria vectors is threatening the effectiveness of insecticide-based interventions, including Long Lasting Insecticidal Nets (LLINs). However, the impact of metabolic resistance on the effectiveness of these tools remains poorly characterized. Using experimental hut trials and genotyping of a glutathione S-transferase resistance marker (L119F-GSTe2), we established that GST-mediated resistance is reducing the efficacy of LLINs against Anopheles funestus. Hut trials performed in Cameroon revealed that Piperonyl butoxide (PBO)-based nets induced a significantly higher mortality against pyrethroid resistant An. funestus than pyrethroid-only nets. Blood feeding rate and deterrence were significantly higher in all LLINs than control. Genotyping the L119F-GSTe2 mutation revealed that, for permethrin-based nets, 119F-GSTe2 resistant mosquitoes have a greater ability to blood feed than susceptible while the opposite effect is observed for deltamethrin-based nets. For Olyset Plus, a significant association with exophily was observed in resistant mosquitoes (OR = 11.7; p < 0.01). Furthermore, GSTe2-resistant mosquitoes (cone assays) significantly survived with PermaNet 2.0 (OR = 2.1; p < 0.01) and PermaNet 3.0 (side) (OR = 30.1; p < 0.001) but not for Olyset Plus. This study shows that the efficacy of PBO-based nets (e.g., blood feeding inhibition) against pyrethroid resistant malaria vectors could be impacted by other mechanisms including GST-mediated metabolic resistance not affected by the synergistic action of PBO. Mosaic LLINs incorporating a GST inhibitor (diethyl maleate) could help improve their efficacy in areas of GST-mediated resistance.

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