Investigation of Malaria Vectors (Diptera: Culicidae) in Agricultural Settlements in the Amazon Region of Brazil

Abstract Background: Environmental changes resulting from the urbanization process represent a challenge for malaria control. The majority of malaria cases in South America occur in rural areas, areas of recent occupation, mining and indigenous areas of the Amazon region. Although these areas have a significant impact on malaria cases, few entomological studies have been carried out in areas of recent occupation. This study aimed to describe the density, natural infection rate and hematophagic behavior of anopheline species in two settlements in the state of Rondonia, Brazil in order to understand how malaria transmission occurs in areas that have been settled at different times.Methods: An area of recent occupation, denominated Acampamento Fortaleza (AF), and an old settlement, denominated Projeto de Assentamento Florestal Jequitibá (PAFJ), were studied. Peridomicile collections of anopheles were carried out using the Protected Human Attraction Technique (PHAT). The risk and potential for malaria transmission were assessed using the human biting rate (HBR), sporozoite rate (SR) and the entomological inoculation rate (EIR).Results: The results confirmed that Nyssorhynchus darlingi, the main vector responsible for the transmission of malaria in the state of Rondônia, is the predominant species in the two studied locations. Although settlement of the two study sites has occurred at different times, the species richness found was low, showing that the environmental changes caused by anthropological actions probably favor the adaptation of the Ny. darlingi species. Of the 615 anopheline mosquitoes assessed, 7 (1.1%) were positive for Plasmodium infections. The EIR revealed that Ny. darlingi contributes to the transmission of malaria in both locations, since it was responsible for 0.41 infectious bites in humans at night in PAFJ and 0.16 in AF. In the two study sites, the biting occurred more frequently at dusk.Conclusions: Ny. darlingi is the principal vector found in the studied locations. Its prevalence occurs in areas of recent colonization but, even when present in a low density, this species could maintain transmission of malaria in an older settlement. The entomological information obtained in this study is important and may aid the selection of vector control actions in these locations that are considered as having a high risk of malaria transmission.

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

10.21203/rs.3.rs-24165/v1 ◽

2020 ◽

Author(s):

Souleymane Doucoure ◽

Omar Thiaw ◽

Amélé N. Wotodjo ◽

Charles Bouganali ◽

Nafissatou Diagne ◽

...

Keyword(s):

Malaria Transmission ◽

Anopheles Funestus ◽

Molecular Techniques ◽

Malaria Vectors ◽

Bed Nets ◽

Low Level ◽

Biting Rate ◽

Outdoor Biting ◽

Night And Day ◽

Biting Behaviour

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 day (7am–11am) periods, the place of biting and the season. The ELISA CSP technique was used to evaluate the entomological inoculation rate (EIR).Results: An. arabiensis and An. funestus s.s. were found to be the main vectors biting human in Dielmo. Overall, the biting rate was low, at 3.84bites per night (bpn) and 1.27 bites per day (bpd), respectively. The EIR was 2.51 and 5.03 infected bites per year during the night and day, respectively. During the night, the An. arabiensis and An. funestus biting rate was 1.81 bpn and 1.71 bpn, respectively (p=0.80). During daylight hours, their aggressiveness decreased to 0.51 bpd and 0.73 bpd for An. arabiensis and An. funestus, respectively (p=0.30). During the night, depending on the seasons, only An. funestus displayed a significant outdoor biting behaviour both in the rainy and dry seasons, while during the day, no specific trend of indoor or outdoor biting was observed, regardless of the 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 programs should increase awareness of the use of bed-nets throughout the year, particularly shortly after dawn when people are still indoors.

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Heterogeneous Exposure and Hotspots for Malaria Vectors at Three Study Sites in Uganda

10.1101/299529 ◽

2018 ◽

Cited By ~ 1

Author(s):

Su Yun Kang ◽

Katherine E. Battle ◽

Harry S. Gibson ◽

Laura V. Cooper ◽

Kilama Maxwell ◽

...

Keyword(s):

Malaria Transmission ◽

Negative Binomial ◽

Critical Evaluation ◽

Housing Quality ◽

Malaria Vectors ◽

Entomological Surveillance ◽

Malaria Exposure ◽

Dry Seasons ◽

Cold Spots ◽

Study Sites

AbstractHeterogeneity in malaria transmission has household, temporal, and spatial components. These factors are relevant for improving the efficiency of malaria control by targeting heterogeneity. To quantify variation, we analyzed mosquito counts from entomological surveillance conducted at three study sites in Uganda that varied in malaria transmission intensity. Using a Bayesian zero-inflated negative binomial model, validated via a comprehensive simulation study, we quantified household differences in malaria exposure and examined its spatial distribution. We found that housing quality explained large variation among households in mosquito counts. In each site, there was evidence for hot and cold spots, spatial patterns associated with urbanicity, elevation, or other environmental covariates. We also found some differences in the hotspots in rainy vs. dry seasons or before vs. after control. This work identified methods for quantifying heterogeneity in malaria exposure and offered a critical evaluation of spatially targeting interventions at malaria hotspots.

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Vectorial Transmission of Malaria in Major Districts of Côte d’Ivoire

Journal of Medical Entomology ◽

10.1093/jme/tjz207 ◽

2019 ◽

Vol 57 (3) ◽

pp. 908-914

Author(s):

Konan F Assouho ◽

Akré M Adja ◽

Négnorogo Guindo-Coulibaly ◽

Emmanuel Tia ◽

Affoué M N Kouadio ◽

...

Keyword(s):

Malaria Transmission ◽

Mass Distribution ◽

Cote D'ivoire ◽

Rural Areas ◽

Urban Areas ◽

Côte D’Ivoire ◽

Anopheles Funestus ◽

Malaria Vectors ◽

Cote D’Ivoire ◽

Côte D'ivoire

Abstract To better understand the influence of periodic mass distribution of Long-Lasting Insecticidal Nets (LLINs) on malaria transmission, a 1-yr entomological survey was conducted in three major districts of Côte d’Ivoire. Mosquitoes were sampled by Human Landing Catches (HLC) in urban and rural areas of San Pedro and Abidjan (coastal), and in Yamoussoukro (central). Mosquitoes were identified morphologically and by molecular methods. The Plasmodium falciparum circumsporozoite (CSP) indices were measured by ELISA, and the Entomological Inoculation Rates (EIR) were calculated for each species and area. Anopheles gambiae s.l. Giles (Diptera: Culicidae) and Anopheles nili Theobald (Diptera: Culicidae) were identified in coastal districts, while An. gambiae s.l. and Anopheles funestus Giles (Diptera: Culicidae) were reported in the central district. In urban areas, malaria vectors showed a low aggressiveness (<10 bites per person per night), except in Yamoussoukro, where up to 18.9 b/p/n were recorded. The annual EIR was higher in the central urban area (138.7 infected bites per person per year) than in coastal ones (10–62 ib/p/n). In rural areas, malaria vectors were highly aggressive with an average 13 b/p/n for An. gambiae s.l, 21.2 b/p/n for An. nili and 12 b/p/n for An. funestus. The annual EIR ranged between 94.9 and 193.4 infected bites per person per year. This work indicates that, despite repeated mass distribution of LLINs, malaria transmission remains high and heterogeneous across Côte d’Ivoire. Malaria transmission was lower in coastal urban areas than in the central one, and remains high rural areas where two additional Anopheles vectors are involved in malaria transmission.

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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 profile and new registers of the genera Anopheles (Diptera, Culicidae) in a Brazilian rural community of the District of Coxipó do Ouro, Cuiabá, Mato Grosso

EntomoBrasilis ◽

10.12741/ebrasilis.v13.e0848 ◽

2020 ◽

Vol 13 ◽

pp. e0848

Author(s):

Adaiane Catarina Marcondes Jacobina ◽

Jozeilton Dantas Bandeira ◽

Fábio Alexandre Leal dos Santos ◽

Elisangela Santana de Oliveira Dantas ◽

Diniz Pereira Leite-Jr

Keyword(s):

Malaria Transmission ◽

Rural Area ◽

Rural Community ◽

The State ◽

Monophyletic Group ◽

Transmission Risk ◽

Vector Species ◽

Entomological Surveillance ◽

Mato Grosso ◽

Principal Vector

The order Diptera is constituted of insects that possess numerous varieties of habitats, these winged, commonly called mosquitoes, comprise a monophyletic group. Malaria transmitters in Brazil are represented by mosquitoes of the Anopheles genus, being it principal vector species Anopheles (Nyssorhynchus) darlingi Root. Collectings were accomplished in the rural area of Cuiabá in the region of Coxipó do Ouro/MT, and a total 4,773 adult mosquitoes of the genus Anopheles were obtained. The prevailing species in the collectings where An. (Nys.) darlingi with 3,905 (81.8%), considered the vector of major epidemiological expression in the region, followed by Anopheles (Nyssorhynchus) argyritarsis (Robineau-Desvoidy) 267 (5.6%) and Anopheles (Nyssorhynchus) triannulatus (Neiva & Pinto) 226 (4.7%). This report might be useful to entomological surveillance, demonstrating that the Coxipó do Ouro/MT locality might be elected as an area to be monitored, once the presence of such vector in this type of environment indicates a potential malaria transmission risk for the neighbouring regions in the state of Mato Grosso.

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

10.21203/rs.3.rs-24165/v2 ◽

2020 ◽

Author(s):

Souleymane Doucoure ◽

Omar Thiaw ◽

Amélé N. Wotodjo ◽

Charles Bouganali ◽

Nafissatou Diagne ◽

...

Keyword(s):

Malaria Transmission ◽

Anopheles Arabiensis ◽

Anopheles Funestus ◽

Sensu Stricto ◽

Molecular Techniques ◽

Malaria Vectors ◽

Bed Nets ◽

Low Level ◽

Biting Rate ◽

Outdoor Biting

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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High malaria transmission sustained by Anopheles gambiae s.l. occurring both indoors and outdoors in the city of Yaoundé, Cameroon

Wellcome Open Research ◽

10.12688/wellcomeopenres.14963.1 ◽

2018 ◽

Vol 3 ◽

pp. 164 ◽

Cited By ~ 8

Author(s):

Patricia Doumbe-Belisse ◽

Carmene Sandra Ngadjeu ◽

Nadege Sonhafouo-Chiana ◽

Abdou Talipouo ◽

Landre Djamouko-Djonkam ◽

...

Keyword(s):

Anopheles Gambiae ◽

Malaria Transmission ◽

Public Health Problem ◽

Transmission Risk ◽

Malaria Vectors ◽

Major Public Health Problem ◽

Infection Status ◽

Mosquito Abundance ◽

Biting Rate ◽

The City

Background: Malaria remains a major public health problem in Cameroon; however, despite reports on the adaptation of anopheline species to urban habitats, there is still not enough information on malaria transmission pattern in urban settings. In the frame of a larval control trial in the city of Yaoundé, we conducted baseline surveys to assess malaria transmission dynamics in this city. Methods: Adult mosquitoes were collected indoors and outdoors using CDC light traps and human landing catches from March 2017 to March 2018 in 30 districts of Yaoundé, Cameroon. Mosquitoes were sorted by genus and identified to the species level using PCR. The TaqMan method and ELISA were used to determine mosquito infection status to Plasmodium. Bioassays were conducted to assess female Anopheles gambiae susceptibility to insecticides. Results: A total of 218,991 mosquitoes were collected. The main malaria vectors were An. gambiae s.l. (n=6154) and An. funestus s.l. (n=229). Of the 1476 An. gambiae s.l. processed by PCR, 92.19% were An. coluzzii and 7.81% An. gambiae. An. funestus s.l. was composed of 93.01% (173/186) An. funestus and 4.84% (13/186) An. leesoni. The average biting rate of anopheline was significantly high outdoor than indoor (P=0.013). Seasonal variation in mosquito abundance and biting rate was recorded. The infection rate by Plasmodium falciparum was 2.13% (104/4893 mosquitoes processed). The annual entomological inoculation rate was found to vary from 0 to 92 infective bites/man/year (ib/m/y). Malaria transmission risk was high outdoor (66.65 ib/m/y) compared to indoor (31.14 ib/m/y). An. gambiae s.l. was found highly resistant to DDT, permethrin and deltamethrin. High prevalence of the West Africa kdr allele 1014F was recorded and this was not found to influence An. gambiae s.l. infection status. Conclusion: The study suggests high malaria transmission occurring in the city of Yaoundé and call for immediate actions to improve control strategies.

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Effect of bendiocarb based (Ficam® 80% WP) Indoor Residual Spraying on feeding patterns of malaria vectors in Burkina Faso, West Africa.

10.21203/rs.3.rs-19216/v1 ◽

2020 ◽

Author(s):

HIEN S. Aristide ◽

Dieudonné Diloma Soma ◽

Simon Pengwende Sawadogo ◽

Serge Bèwadéyir Poda ◽

Moussa Namountougou ◽

...

Keyword(s):

Burkina Faso ◽

Malaria Transmission ◽

Malaria Vector ◽

Light Trap ◽

Indoor Residual Spraying ◽

Malaria Vectors ◽

Feeding Patterns ◽

Transmission Season ◽

Cdc Light Trap ◽

Biting Rate

Abstract Background : Vector control is a key component in malaria prevention strategies in many malaria endemic countries in Africa. In Burkina Faso, malaria transmission is seasonal in most parts of country, so a single round of spraying should provide effective protection against malaria, provided the insecticide remains effective over the entire malaria transmission season. The primary effects of IRS towards curtailing malaria transmission are : i) to reduce the life span of vector mosquitoes and ii) to reduce the density of the vector mosquitoes. Methods : CDC light trap and pyrethrum spray catches were carried out monthly to determine the change in malaria vector indices in sprayed (Diebougou) and unsprayed sites (Dano). The females malaria vectors collected by CDC light trap and PSC were used to determine their blood feeding and sporozoites rate using enzyme-linked immunosorbent assay (ELISA) and their biting rate and entomological inoculation rateResults: Three species belonging to the Anopheles gambiae complex (Anopheles gambiae s.s., Anopheles coluzzii and Anopheles arabiensis) are present throughout the transmission season, but An. gambiae s.s.was the most frequent species of the complex (P =0.0005), comprising 88% of the total collected and the most infected species. Malaria vectors densities were significantly lower in sprayed villages (n=4,303) compared with unsprayed villages (n=12,569) during post-spraying period (P = 0.0012). In addition, mean human biting rate of An. gambiae sl and An. funestus ss were significantly lower in sprayed areas compared to unsprayed areas (P<0.05). Overall, malaria vector transmission risk was significant lower in villages which received IRS (P=0.0001) whatever the malaria vectors species (An. gambiae sl and An. funestus ss).Conclusion: The results showed that in the sprayed area (Diebougou), vector densities, human biting rates and malaria transmission risks were very lower than unsprayed areas (Dano). The findings also showed a change in vector behavior especially within An. funestus which became more zoophagic following IRS. The indoor residual spraying could be recommanded as control tool in areas where malaria transmission occured throughout the year.Keywords: Indoor residual spraying, bendiocarb, malaria vectors, mosquito feeding patterns, Burkina Faso.

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