Adult Anopheles Mosquito Distribution at a Low and High Malaria Transmission Site in Tanzania

Malaria parasites are only transmitted by female mosquitoes of the genus Anopheles; hence, the disease’s distribution is linked to that of the vector mosquitoes. As such, the goal of this study was to find out the spatial and temporal distribution of Anopheles mosquito adults in the research sites. This was a repeated cross-sectional ecological study that took place in Morogoro and Dodoma, Tanzania. Vacuum aspiration was used to collect mosquitoes both outside and inside human dwellings. All mosquito-related data was collected and entered into appropriate data collection forms. Female mosquitoes were recognized morphologically using Gillies and Coetzee morphological criteria, followed by PCR. In total, about 2742 Anopheles mosquitoes with an average collection of 18.21 ± 1.12 per day were collected outside human houses of which 1717 ( 10.51 ± 1.17 ) and 1025 ( 8.42 ± 1.41 ) were collected from Morogoro and Dodoma, respectively. Of the captured mosquitoes, 89.0%, 10.0%, and 1.0% were recognized as Anopheles arabiensis, Anopheles gambiae s.s., and Anopheles quadrianulatus, respectively. The distribution varied significantly with seasons, whereby 302 ( 4.72 ± 1.04 ) and 2440 ( 12.96 ± 1.52 ) mosquitoes were captured in the cold-dry and warm-wet season, respectively ( p < 0.0001 ). Of the captured mosquitoes, 42.33%, 16.33%, 14.96%, and 4.27 were found on the ceiling, stored junks, verandas, and barks/tree, respectively. In malaria-endemic countries, vector control forms an important component of the malaria control efforts. This study found significant variation of Anopheles mosquito abundance in time and space with Anopheles arabiensis being the most predominant malaria vector. This signifies the need to introduce mosquito control methods that will target the less anthropophilic Anopheles arabiensis or the immature aquatic stages. The study further found that underbeds, store room/piled bags, and undisturbed curtains were the most preferred resting places by mosquitoes signifying to be the most effective strategic sites for spraying insecticides during the implementation of indoor residual spraying (IRS).

The Centres for Disease Control Light Trap (CDC LT) and The Human Decoy Trap (HDT) Compared to The Human Landing Catch (HLC) for Measuring Anopheles Biting in Rural Tanzania

BackgroundThe intensity of vector mosquito biting is an important measure for malaria epidemiology and control. The human landing catch (HLC) is an effective entomological surveillance tool, but is labour-intensive, expensive and raises safety issues. The Centres for Disease Control light trap (CDC LT) and the human decoy trap (HDT) are less costly and exposure-free alternatives. This study compared the CDC LT and HDT against the HLC for measuring Anopheles (An.) biting in rural Tanzania and assessed their suitability as HLC proxies.MethodsIndoor mosquito surveys using HLC and CDC LT and outdoor surveys using HLC and HDT were conducted in 2017 and in 2019 in Ulanga, Tanzania in 19 villages, with one trap per house per night. Species composition, sporozoite rates and the numbers of mosquitoes caught by different trap types were compared. Aggregating the data by village and month, the Bland-Altman approach was used to assess agreement. ResultsOverall, 66,807 Anopheles funestus and 14,606 An. arabiensis adult females were caught from 6,013 CDC LT, 339 indoor HLC, 136 HDT and 195 outdoor HLC collections. Overall, the CDC LT caught fewer malaria vectors than indoor HLC: An. arabiensis (Adjusted rate ratio (Adj.RR) =0.35 (95% confidence interval (CI):0.27-0.46)) and An. funestus (Adj.RR=0.63(95%CI:0.51-0.79)). HDT caught fewer malaria vectors than outdoor HLC: An. arabiensis (Adj.RR=0.04(95%CI:0.01-0.14)) and An. funestus (Adj.RR=0.10(95%CI:0.07-0.15)). The bias and variability of the ratios of geometric mean mosquitoes caught by CDC LT and HDT relative to HLC collections for the same village-month were dependent on mosquito densities. The relative efficacies of both CDC LT and HDT declined with mosquito abundance. The variability in the ratios was substantial for low HLC counts and decreased as mosquito abundance increased. CDCLT caught a higher proportion of infected An. arabiensis and An. funestus than HLC, and HDT caught no infected mosquitoes.ConclusionsIf caution is taken in appreciation of its limitations, the CDC LT is suitable for use in routine entomological surveys and may be preferable for measuring sporozoite rates for Afrotropical mosquitoes. Use of HLC is useful to estimate human exposure to mosquitoes for estimating Entomological Inoculation Rate (EIR). The present design of the HDT is not amenable for use to conduct large-scale entomological surveys.

Effects of land use and weather on the presence and abundance of mosquito-borne disease vectors in a urban and agricultural landscape in Eastern Ontario, Canada

Weather and land use can significantly impact mosquito abundance and presence, and by consequence, mosquito-borne disease (MBD) dynamics. Knowledge of vector ecology and mosquito species response to these drivers will help us better predict risk from MBD. In this study, we evaluated and compared the independent and combined effects of weather and land use on mosquito species occurrence and abundance in Eastern Ontario, Canada. Data on occurrence and abundance (245,591 individuals) of 30 mosquito species were obtained from mosquito capture at 85 field sites in 2017 and 2018. Environmental variables were extracted from weather and land use datasets in a 1-km buffer around trapping sites. The relative importance of weather and land use on mosquito abundance (for common species) or occurrence (for all species) was evaluated using multivariate hierarchical statistical models. Models incorporating both weather and land use performed better than models that include weather only for approximately half of species (59% for occurrence model and 50% for abundance model). Mosquito occurrence was mainly associated with temperature whereas abundance was associated with precipitation and temperature combined. Land use was more often associated with abundance than occurrence. For most species, occurrence and abundance were positively associated with forest cover but for some there was a negative association. Occurrence and abundance of some species (47% for occurrence model and 88% for abundance model) were positively associated with wetlands, but negatively associated with urban ( Culiseta melanura and Anopheles walkeri ) and agriculture ( An. quadrimaculatus, Cs. minnesotae and An. walkeri ) environments. This study provides predictive relationships between weather, land use and mosquito occurrence and abundance for a wide range of species including those that are currently uncommon, yet known as arboviruses vectors. Elucidation of these relationships has the potential to contribute to better prediction of MBD risk, and thus more efficiently targeted prevention and control measures.

Ecological Characterization of Mosquitoes (Diptera: Culicidae) at the Southern Coast of Mar Chiquita Lake, Argentina

In the southern coast of Mar Chiquita Lake, central Argentina, mosquitoes affect public health and community livelihood, since they transmit pathogens to human beings causing diseases such as malaria, filariasis, encephalitis, yellow fever, and dengue, among others, and have a negative effect on cattle farming as well. To characterize the structure of the mosquito assemblage of the region, we determined the species composition and diversity, the temporal distribution of different species, and the patterns of species richness, abundance, and diversity across seasons. We collected adult mosquitoes over a two-year period (October 2004–September 2006) by means of CDC light traps baited with CO2 from 18:00 to 08:00 h during the warm season (October–April) and from 12:00 h to 18:00 h in the cold season (May–September). A total of 71,501 individuals from 30 species were collected, with Culex Linnaeus and Aedes Meigen genera representing more than 98% of collected specimens (61.5% and 37.3%, respectively). The higher values of richness and abundance of Culicidae were registered in warm seasons compared to cold seasons. Chao1 estimates suggested that more than 90% of the species were detected in all seasons. Mosquito abundance distribution fit the logarithmic series and log-normal models. Aedes albifasciatus (Macquart), Ae. scapularis (Rondani), Culex interfor Dyar, Cx. saltanensis Dyar, and Cx. dolosus (Lynch Arribálzaga), vectors incriminated in arbovirus transmission, were abundant year-round, with Cx. saltanensis and Cx. dolosus most prevalent in cold seasons. Further studies are needed to assess the role of these species in arbovirus transmission in this region of central Argentina.

Bionomics of Aedes aegypti during the 2016-2017 dengue outbreaks in Ouagadougou, Burkina Faso.

Dengues emergence in West Africa was typified by the Burkina Faso outbreaks in 2016 and 2017, the nation's largest to date. In both years, we undertook three-month surveys of Aedes populations in or near the capital city Ouagadougou, where the outbreak was centered. In urban, peri-urban and rural localities we collected indoor and outdoor resting mosquito adults, characterized larval habitats and containers producing pupae and reared immature stages to adulthood in the laboratory for identification. All mosquito adults were identified morphologically. Host species from which bloodmeals were taken were identified by PCR Generalized mixed models were used to investigate relationships between adult or larval densities and multiple explanatory variables. From samples in 1,791 houses, Ae. aegypti was the most abundant mosquito in the two urban localities where it occurred in 46% of containers sampled and comprised over 85% of collections. Results indicated a highly exophilic and anthropophilic (>90% bloodmeals of human origin) vector population, but with a relatively high proportion of bloodfed females caught inside houses. Habitats producing most pupae were waste tires (37% of total pupae), animal troughs (44%) and large water barrels (30%). While Stegomyia indices were not reliable indicators of adult mosquito abundance, shared influences on adult and immature stage densities included rainfall and container water level, collection month and container type/ purpose. Spatial analysis showed autocorrelation of densities, with partial overlap in adult and immature stage hotspots. Results provide an evidence base for the selection of appropriate vector control methods to minimize the risk, frequency and magnitude of future outbreaks in Ouagadougou. An integrated strategy combining community-driven practices, waste disposal and insecticide-based interventions is indicated. The prospects of developing a regional approach to arbovirus control in west Africa or across Africa was discussed.

Aedes-AI: Neural network models of mosquito abundance

We present artificial neural networks as a feasible replacement for a mechanistic model of mosquito abundance. We develop a feed-forward neural network, a long short-term memory recurrent neural network, and a gated recurrent unit network. We evaluate the networks in their ability to replicate the spatiotemporal features of mosquito populations predicted by the mechanistic model, and discuss how augmenting the training data with time series that emphasize specific dynamical behaviors affects model performance. We conclude with an outlook on how such equation-free models may facilitate vector control or the estimation of disease risk at arbitrary spatial scales.

Relationship of Climatic Variables with Abundance of Indoor Mosquito Genera in Six Communities in Ekiti State, Nigeria

Understanding the relationship between climate variables and mosquito abundance is an important factor to determine parasite activity levels and disease risk since various mosquito genera are vectors of parasitic diseases. This necessitated the investigation of relationship between climatic variables and mosquito abundance in Ekiti State, Nigeria with reference to six selected communities. Adult mosquitoes were collected indoor for twelve months in these communities using light traps. The abundance of collected mosquitoes was related with climatic variables (rainfall, relative humidity and temperature). One thousand two hundred and seventeen (1217) adult mosquitoes were collected indoor in all the communities. The population of the mosquito genera was significantly higher (P=0.01) in rainy season than dry season. Average rainfall showed a strong relationship (R2= 0.751) with Anopheles abundance but relationship was weak for both Culex (R2= 0.236) and Aedes (R2= 0.042). The relationship of relative humidity and average temperature with abundance of mosquito genera was generally weak. Since the abundance of mosquito genera was higher in all the communities during rainy season than dry season it will be more appropriate to control mosquitoes in the communities during the rainy season.

Mosquito abundance in relation to extremely high temperatures in urban and rural areas of Incheon Metropolitan City, South Korea from 2015 to 2020: an observational study

Background Despite concerns regarding increasingly frequent and intense heat waves due to global warming, there is still a lack of information on the effects of extremely high temperatures on the adult abundance of mosquito species that are known to transmit vector-borne diseases. This study aimed to evaluate the effects of extremely high temperatures on the abundance of mosquitoes by analyzing time series data for temperature and mosquito abundance in Incheon Metropolitan City (IMC), Republic of Korea, for the period from 2015 to 2020. Methods A generalized linear model with Poisson distribution and overdispersion was used to model the nonlinear association between temperature and mosquito count for the whole study area and for its constituent urban and rural regions. The association parameters were pooled using multivariate meta-regression. The temperature–mosquito abundance curve was estimated from the pooled estimates, and the ambient temperature at which mosquito populations reached maximum abundance (TMA) was estimated using a Monte Carlo simulation method. To quantify the effect of extremely high temperatures on mosquito abundance, we estimated the mosquito abundance ratio (AR) at the 99th temperature percentile (AR99th) against the TMA. Results Culex pipiens was the most common mosquito species (51.7%) in the urban region of the IMC, while mosquitoes of the genus Aedes (Ochlerotatus) were the most common in the rural region (47.8%). Mosquito abundance reached a maximum at 23.5 °C for Cx. pipiens and 26.4 °C for Aedes vexans. Exposure to extremely high temperatures reduced the abundance of Cx. pipiens mosquitoes {AR99th 0.34 [95% confidence interval (CI) 0.21–0.54]} to a greater extent than that of Anopheles spp. [AR99th 0.64 (95% CI 0.40–1.03)]. When stratified by region, Ae. vexans and Ochlerotatus koreicus mosquitoes showed higher TMA and a smaller reduction in abundance at extreme heat in urban Incheon than in Ganghwa, suggesting that urban mosquitoes can thrive at extremely high temperatures as they adapt to urban thermal environments. Conclusions We confirmed that the temperature-related abundance of the adult mosquitoes was species and location specific. Tailoring measures for mosquito prevention and control according to mosquito species and anticipated extreme temperature conditions would help to improve the effectiveness of mosquito-borne disease control programs. Graphical abstract

Seasonal Prevalence and Host Preference of Some Medically Important Aedes Species of Doon Valley, India

In the recent past, several outbreaks of mosquito-borne diseases in Dehradun city make it necessary for a comprehensive understanding of man-vector contacts, disease transmission and determination of appropriate resting sites for adult mosquitoes. The study was conducted within the periphery of Dehradun city in Doon valley, Uttarakhand state, India consisting of eight (08) locations namely Sahaspur, Premnagar, Raipur, Karanpur, Sahastradhara, Dudhli, Doiwala and Rani Pokhri with the objective to analyze and assess the seasonal prevalence and host choice of the mosquitoes with special reference to Aedes species. Among the eight locations of the current study, Raipur registered the highest mosquito abundance (17%) trailed by Sahaspur (16%) and Karanpur (15%). A low abundance of mosquitoes was registered conjointly from Doiwala and Rani Pokhri areas (9% from each area). In these areas, the profile plots of the 2-way ANOVA displayed the highest variation for the data collected from human habitations followed by bovine sheds, whereas the lowest recorded variation was from the poultry. With regards to seasonal prevalence, the highest mosquito abundance was registered during the monsoon followed by the post-monsoon. In provender analysis, a total of 1912 blood meals were collected for antibody test among which 1851 were found positive, with the highest reaction with human antisera (57.75%), followed by bovine antisera (21.34%) and pigs antisera (4.97%). Ae. aegyptihad the highest Anthropophilic Index (A.I.) with 68.78%, followed by Ae. albopictus (64.89%) and Ae. vittatus (55.55%). However, Human Blood Predominance (H.B.P.) and Pure Human Blood Pervasiveness (P.H.B.P.) were found highest for Ae. albopictus with values 0.43 and 0.44 respectively. The results also show the seasonal prevalence and feeding habits of these vectors. This study would be helpful in formulating season-wise strategies for the control of Aedes vector mosquitoes in different eco-epidemiological situations.

Aedes Mosquito Distribution along a Transect from Rural to Urban Settings in Yaoundé, Cameroon

Introduction: The surveillance of mosquito vectors is important for the control of arboviruses diseases worldwide. Detailed information on the bionomics and distribution of their main vectors, Aedes aegypti and Aedes albopictus, is essential for assessing disease transmission risk and for better planning of control interventions. Methods: Entomological surveys were carried out from November 2019 to November 2020 in six localities of Yaoundé city following a transect from urban to rural settings: two urban (Obili, Mvan), two peri-urban (Simbock, Ahala) and two rural areas (Lendom, Elig-essomballa)—during rainy and dry seasons. All water containers were inspected. Aedes mosquito abundance, species distribution and seasonal distribution patterns were compared using generalized linear models. Stegomyia indexes were estimated to determine the risk of arbovirus transmission. Results: A total of 6332 mosquitoes larvae were collected (2342 in urban areas, 1694 in peri-urban areas and 2296 in rural sites). Aedes species recorded included Ae. albopictus, Ae. aegytpi, Ae. simpsoni and Aedes spp. High mosquito abundance was registered in the rainy season (4706) compared to the dry season (1626) (p < 0.0001). Ae. albopictus was the most abundant Aedes species in urban (96.89%) and peri-urban (95.09%) sites whereas Ae. aegypti was more prevalent in rural sites (68.56%) (p < 0.0001). Both species were found together in 71 larval habitats. Ae. albopictus was mostly found in discarded tires (42.51%), whereas Ae. aegypti was more prevalent in plastic containers used for storing water (65.87%). The majority of Aedes mosquitoes’ breeding places were situated close to human dwellings (0–10 m). Conclusion: Uncontrolled urbanization seems to greatly favour the presence of Aedes mosquito species around human dwellings in Yaoundé. Controlling Aedes mosquito distribution is becoming urgent to reduce the risk of arbovirus outbreaks in the city of Yaoundé.