Large-Scale Deployment of Pyriproxyfen-Treated Lehmann Funnel Entry Traps to Control Malaria Mosquito Populations

Background: The Lehmann Funnel Entry Trap has proven to be effective in catching and killing up to 70% of mosquitoes even in a high mosquito density setting. A medium-sized prototype was selected and deployed at large scale in Vallée du Kou 3 (VK3) in the Southwest of Burkina Faso to assess its entomological and sociological impact.Method: Overall, 1,313 traps impregnated with Pyriproxyfen (PPF), were deployed. Of them, 12 traps were randomly selected across the intervention village compared to houses without traps in the control village, Vallée du Kou 5 (VK5). Traps were placed at the windows while doors were blocked with curtains. Mosquitoes were collected in traps and matching houses in VK3 and in houses only in VK5, for nine days per month from July to October 2015. Collected mosquitoes were morphologically identified, counted, and preserved in 80% ethanol vials for subsequent analyses, including resistance genes and female mosquito age structure. The impact of the trap on mosquito density at community level was assessed by performing a pyrethrum spray catch (PSC) with bioassays to assess the effect of PPF. Results: Overall mosquito density was reduced by ~90% in all houses equipped with traps in VK3. At the community level, while mosquito density before intervention was 33% higher in VK3 than in VK5, it was 47% higher in VK5 after the intervention. Old female mosquito numbers increased in VK5 by 12% in October but not in VK3, indicating that the traps were cumulatively killing old females. The additional effect of PPF was to limit egg-laying, with a smaller number of eggs counted, and with a low hatching rate. Mosquitoes were highly resistant to pyrethroids with ~0.9 frequency of the kdr mutation. The trap was well accepted by the communities as 85.4% and 93.8% of interviewees in VK3 found the traps reducing mosquito bites with peaceful sleep respectively. Conclusion: The Lehmann Funnel Entry Trap has real potential to control malaria mosquito populations and can be widely used to sustain the global effort of malaria elimination.

Estimating the Mosquito Density in Guangzhou city, China

Mosquito is a vector of many diseases. Predicting the trend of mosquito density is important for early warning and control of mosquito diseases. In this paper, we fit a discrete time mosquito model developed by Gong et al. in 2011, which considers the immature and adult stages, and weather dependent model parameters, to the Breteau Index and Bite Index data for Aedes aegypti in Guangzhou city, China in 2014, as well as the weather data for average temperature, precipitation, evaporation and daylight for the same period. We estimated the model parameters using the Markov Chain Monte-Carlo (MCMC) method. We find that many parameters are not identifiable. We revise and simplify the model so that the parameters of our new model are identifiable. Our results indicate that the model predicted mosquito prevalence agrees well with data. We then use the fitted parameter values against the Breteau Index and Bite Index data for Guangzhou city in 2017 and 2018, and show that the estimated parameter values are applicable for other seasons.

Spatial Mapping of Aedes Sp. Densities and Endemicity Level of Dengue in Three Villages in South Sulawesi, Indonesia

The study aim to analyze the spatial map of the density of Aedes sp., several measurement methods, and the relationship between environmental factors with mosquito density in Makassar City, Maros and Gowa Cities. The research method used an ecological study design. In this study, surveys of larvae, ovitrap and Lighttrap were be used to measure the density of Aedes sp. Data processing using SPSS version 22 and Arview GIS 10.5. The results that spatial analysis showed a random pattern or spread of density of larvae, ovitrap and adult mosquitoes. the Larva and Ovitrap survey methods were specific measured the density of Dengue vectors (larvae, eggs and adult mosquitoes Aedes aegypti) while the Light Trap method was not specific. There was a significant relationship between temperature, humidity and egg density and Aedes aegypti mosquitoes in three DHF endemic sub-districts; except humidity and mosquito density was not significant in Bontoa Village of Maros Regency (p> 0.05). There was no significant relationship between the wire netted ventilation factor and the density of Aedes aegypti mosquitoes in the three DHF endemic sub-districts except for the mosquito density there was a significant relationship in Bontoa Village, Maros Regency.

Determinants of Aedes mosquito density as an indicator of arbovirus transmission risk in three sites affected by co-circulation of globally spreading arboviruses in Colombia, Ecuador and Argentina

Background The global impact of Zika virus in Latin America has drawn renewed attention to circulating mosquito-borne viruses in this region, such as dengue and chikungunya. Our objective was to assess socio-ecological factors associated with Aedes mosquito vector density as a measure of arbovirus transmission risk in three cities of potentially recent Zika virus introduction: Ibagué, Colombia; Manta, Ecuador; and Posadas, Argentina, in order to inform disease mitigation strategies. Methods We sampled Aedes mosquito populations in a total of 1086 households, using indoor and peridomestic mosquito collection methods, including light traps, resting traps, traps equipped with chemical attractant and aspirators. For each sampled household, we collected socio-economic data using structured questionnaires and data on microenvironmental conditions using iButton data loggers. Results A total of 3230 female Aedes mosquitoes were collected, of which 99.8% were Aedes aegypti and 0.2% were Aedes albopictus. Mean female Aedes mosquito density per household was 1.71 (standard deviation: 2.84). We used mixed-effects generalized linear Poisson regression analyses to identify predictors of Aedes density, using month, neighborhood and country as random-effects variables. Across study sites, the number of household occupants [incidence rate ratio (IRR): 1.08, 95% confidence interval (CI): 1.01–1.14], presence of entry points for mosquitoes into the household (IRR: 1.51, 95% CI: 1.30–1.76) and presence of decorative vegetation (IRR: 1.52, 95% CI: 1.22–1.88) were associated with higher Aedes density; while being in the highest wealth tertile of household wealth (IRR: 0.78, 95% CI: 0.66–0.92), knowledge of how arboviruses are transmitted (IRR: 0.94, 95% CI: 0.89–1.00) and regular emptying of water containers by occupants (IRR: 0.79, 95% CI: 0.67–0.92) were associated with lower Aedes density. Conclusions Our study addresses the complexities of arbovirus vectors of global significance at the interface between human and mosquito populations. Our results point to several predictors of Aedes mosquito vector density in countries with co-circulation of multiple Aedes-borne viruses, and point to modifiable risk factors that may be useful for disease prevention and control. Graphical Abstract

Entomological characterization of Aedes mosquitoes and arbovirus detection in Ibagué, a Colombian city with co-circulation of Zika, dengue and chikungunya viruses

Background Dengue, Zika and chikungunya are arboviruses of significant public health importance that are transmitted by Aedes aegypti and Aedes albopictus mosquitoes. In Colombia, where dengue is hyperendemic, and where chikungunya and Zika were introduced in the last decade, more than half of the population lives in areas at risk. The objective of this study was to characterize Aedes spp. vectors and study their natural infection with dengue, Zika and chikungunya in Ibagué, a Colombian city and capital of the department of Tolima, with case reports of simultaneous circulation of these three arboviruses. Methods Mosquito collections were carried out monthly between June 2018 and May 2019 in neighborhoods with different levels of socioeconomic status. We used the non-parametric Friedman, Mann–Whitney and Kruskal–Wallis tests to compare mosquito density distributions. We applied logistic regression analyses to identify associations between mosquito density and absence/presence of breeding sites, and the Spearman correlation coefficient to analyze the possible relationship between climatic variables and mosquito density. Results We collected Ae. aegypti in all sampled neighborhoods and found for the first time Ae. albopictus in the city of Ibagué. A greater abundance of mosquitoes was collected in neighborhoods displaying low compared to high socioeconomic status as well as in the intradomicile compared to the peridomestic space. Female mosquitoes predominated over males, and most of the test females had fed on human blood. In total, four Ae. aegypti pools (3%) were positive for dengue virus (serotype 1) and one pool for chikungunya virus (0.8%). Interestingly, infected females were only collected in neighborhoods of low socioeconomic status, and mostly in the intradomicile space. Conclusions We confirmed the co-circulation of dengue (serotype 1) and chikungunya viruses in the Ae. aegypti population in Ibagué. However, Zika virus was not detected in any mosquito sample, 3 years after its introduction into the country. The positivity for dengue and chikungunya viruses, predominance of mosquitoes in the intradomicile space and the high proportion of females fed on humans highlight the high risk for arbovirus transmission in Ibagué, but may also provide an opportunity for establishing effective control strategies. Graphical abstract

Efficacy Bacillus thuringiensis var. israelensis serotype H-14 (Bti H-14) for control Aedes spp. density in Denpasar, Bali

Background: A liquid bioinsecticide formulation containing Bacillus thuringiensis var. israelensis Serotype H-14 (Bti H-14) was tested in the field in household containers. The aim was to determine the effectiveness of Bti H-14 biolarvicide in controlling the density of Aedes spp. Larvae.Methods: This study was conducted in two phases of testing. First, to test the effective dose with 5 doses, namely (50 ul, 40 ul, 30 ul, 20 ul, and 10 ul) in 2.5 liters of water. Furthermore, the number of deaths was calculated after 24 hours of treatment and control by doing four repetitions. In the second phase, by conducting tests on containers in the household as many as 3171 containers were continuously observed every month, given Bti H-14 for 6 months. Observations were made before and after the application of Bti H-14 on larva density, mosquito density, and dengue cases. Data analysis was performed using paired t-test. Bti H-14 formulation to kill 50% of mosquito larvae (LC50) within 6 hours requires a concentration of 4 µl per liter.Results: Bti H-14 liquid formulation with delta-endotoxin and spores content of 600 ITU per ml or 1.2x109 CFU is effective in reducing larva density in household containers if done regularly.Conclusions: Bti H-14 liquid formulation is proven to be effective and easy to use for the control of Aedes larvae.

PEMETAAN KASUS DEMAM BERDARAH DENGUE DAN KEPADATAN NYAMUK BERDASARKAN SISTEM INFORMASI GEOGRAFIS (SIG) DI WILAYAH KERJA PUSKESMAS LHOKNGA KABUPATEN ACEH BESAR

Demam berdarah dengue (DBD) merupakan penyakit menular yang disebabkan oleh virus dengue dari genus flavivirus yang ditularkan melalui gigitan nyamuk Aedes aegypti. Penelitian ini bertujuan untuk melakukan pemetaan kasus penyakit DBD, pemetaan kepadatan nyamuk berdasarkan HI (House Index), CI (Container Index), BI (Breteau Index) dan mengetahui buffer zone sebaran kejadian penyakit DBD di wilayah kerja Puskesmas Lhoknga. Penelitian menggunakan metode deskriptif dengan pendekatan observasi yang disajikan dengan Sistem Informasi Geografis (SIG) untuk mendapatkan distribusi spasial kasus DBD. Jumlah populasi adalah seluruh penderita DBD di Kecamatan Lhoknga tahun 2017-2018. Jumlah sampel sebanyak 41 orang pada bulan Maret 2019. Hasil penelitian menunjukkan bahwa terjadinya penurunan kasus DBD dari tahun 2017 sampai 2018 dikarenakan meningkatnya kesadaran masyarakat mengenai kebersihan lingkungan. Untuk hasil kepadatan nyamuk berdasarkan HI, CI dan BI didapatkan rata-rata Density Figure (DF) sebesar 4,7 artinya kepadatan jentik nyamuk adalah sedang. Kesimpulan: ada penurunan kasus DBD dari tahun 2017 hingga 2018, kepadatan nyamuk adalah sedang serta zona buffer yang sudah terdata. Dengue hemorrhagic fever (DHF) is an infectious disease caused by the dengue virus from the flavivirus genus which is transmitted through the bite of the Aedes aegypti mosquito. This study aimed to map cases of dengue disease, to map mosquito density based on the HI (House Index), CI (Container Index), BI (Breteau Index) and to determine the buffer zone for the spread of dengue disease in the Lhoknga Health Center work area. This research used a descriptive method with an observational approach presented with a Geographic Information System (GIS) to obtain a spatial distribution of DHF cases. The total population is all DHF sufferers in Lhoknga District in 2017-2018. The number of samples was 41 people in March, 2019. The results showed that there was a decrease in DHF cases from 2017 to 2018, due to increased public awareness about environmental cleanliness. The results of mosquito density based on HI, CI and BI were obtained Density Figure (DF) is as much as 4.7, which means that the larva density is moderate. The conclusion is that there was a decrease in DHF cases from 2017 to 2018, the mosquito density is moderate and the buffer zone has been recorded.

Optimization of the feeding rate of Anopheles farauti s.s. colony mosquitoes in direct membrane feeding assays

Background Direct membrane feeding assays (DMFA) are an important tool to study parasite transmission to mosquitoes. Mosquito feeding rates in these artificial systems require optimization, as there are a number of factors that potentially influence the feeding rates and there are no standardized methods that apply to all anopheline species. Methods A range of parameters prior to and during direct membrane feeding (DMF) were evaluated for their impact on Anopheles farauti sensu stricto feeding rates, including the starving conditions and duration of starving prior to feeding, membrane type, DMF exposure time, mosquito age, feeding in the light versus the dark, blood volume, mosquito density and temperature of water bath. Results The average successful DMFA feeding rate for An. farauti s.s. colony mosquitoes increased from 50 to 85% when assay parameters were varied. Overnight starvation and Baudruche membrane yielded the highest feeding rates but rates were also affected by blood volume in the feeder and the mosquito density in the feeding cups. Availability of water during the pre-feed starvation period did not significantly impact feeding rates, nor did the exposure duration to blood in membrane feeders, the age of mosquitoes (3, 5 and 7 days post-emergence), feeding in the light versus the dark, or the temperature (34 °C, 38 °C, 42 °C and 46 °C) of the water bath. Conclusion Optimal feeding conditions in An. farauti s.s. DMFA were to offer 50 female mosquitoes in a cup (with a total surface area of ~ 340 cm2 with 1 mosquito/6.8 cm2) that were starved overnight 350–500 µL of blood (collected in heparin-coated Vacutainer tubes) per feeder in feeders with a surface area ~ 5 cm2 (with a maximum capacity of 1.5 mL of blood) via a Baudruche membrane, for at least 10–20 min. Graphical Abstract

Ownership and utilization of bed nets and reasons for use or non-use of bed nets among community members at risk of malaria along the Thai-Myanmar border

Background With the goal for malaria elimination in Thailand set for 2024, increased coverage and utilization of bed net, especially insecticide-treated net (ITN) or long-lasting insecticidal net (LLIN) is a key strategy. This study aims to provide the necessary information about bed net ownership and utilization among the population at risk of malaria living along the Thai-Myanmar border in Tak province. Methods A cross-sectional study was conducted using a mixed-method approach in 331 households from 5 hamlets in the villages of the Thai-Myanmar border. The research tools included a questionnaire, bed net inspection, and semi-structured interviews. Logistic regression was used to explore the sociodemographic factors associated with bed net utilization. The qualitative analysis employed a thematic analysis approach. Results This survey found that 98.5% of households had at least one bed net per household, and 74.3% had at least one ITN/LLIN. However, only 30.8% of households reached the standard policy set by the Minister of Public Health of one ITN/LLINs per two persons. Most residents used bed net (92.1% used in the previous night and 80.9% used every day). For those using bed nets, however, 61.9% used ITNs or LLINs the night before and 53.1% used them every day. Nonetheless, the usage rates of bed nets (any type) in the previous night among children and pregnant women were high, reaching 95.3% and 90.0%, respectively. Seven explanatory variables showed statistically significant associations with bed net use every day, including: “not staying overnight in the forest or the field”, “sleeping pattern based on gender”, “sufficient numbers of bed nets to cover all sleeping spaces”, “preference for free bed nets”, “age”, “gender”, and “SES score” showed statistically significant association with bed net use every day. The major reasons for the regular use of bed nets in both household and the forest were to prevent mosquito biting. The reasons for not using bednets in the household were discomfort feelings from heat, perception of unnecessity due to low mosquito density, whereas the reason for not using bed nets in the forest was inconvenience. Conclusion Despite that overall coverage and usage of bed nets was high, only one third reached the standard level specified by the policy. Overnight in the forest, the dissatisfaction with the quality of free bed nets, insufficient number of bed nets, sleeping alone, male gender, age more than 10 years, low socioeconomic status, discomfort from heat, perception of no benefits of bed nets due to low mosquito density, and inconvenience were factors influencing bed net use. Maintaining high coverage and utility rate of bed nets should be a priority for the malaria high-risk population.

Serological biomarker for assessing human exposure to Aedes mosquito bites during a randomized vector control intervention trial in northeastern Thailand

Background Aedes mosquitoes are vectors for several major arboviruses of public health concern including dengue viruses. The relationships between Aedes infestation and disease transmission are complex wherein the epidemiological dynamics can be difficult to discern because of a lack of robust and sensitive indicators for predicting transmission risk. This study investigates the use of anti-Aedes saliva antibodies as a serological biomarker for Aedes mosquito bites to assess small scale variations in adult Aedes density and dengue virus (DENV) transmission risk in northeastern Thailand. Individual characteristics, behaviors/occupation and socio-demographics, climatic and epidemiological risk factors associated with human-mosquito exposure are also addressed. Methods The study was conducted within a randomized clustered control trial in Roi Et and Khon Kaen provinces over a consecutive 19 months period. Thirty-six (36) clusters were selected, each of ten houses. Serological and entomological surveys were conducted in all houses every four months and monthly in three sentinel households per cluster between September 2017 and April 2019 for blood spot collections and recording concurrent immature and adult Aedes indices. Additionally, the human exposure to Aedes mosquito bites (i.e., Mosquito Exposure Index or MEI) was estimated by ELISA measuring levels of human antibody response to the specific Nterm-34 kDa salivary antigen. The relationships between the MEI, vector infestation indices (adult and immature stages) and vector DENV infection were evaluated using a two-level (house and individual levels) mixed model analysis with one-month lag autoregressive correlation. Results There was a strong positive relationship between the MEI and adult Aedes (indoor and outdoor) density. Individuals from households with a medium mosquito density (mean difference: 0.091, p<0.001) and households with a high mosquito density (mean difference: 0.131, p<0.001) had higher MEI’s compared to individuals from households without Aedes. On a similar trend, individuals from households with a low, medium or high indoor Aedes densities (mean difference: 0.021, p<0.007, 0.053, p<0.0001 and 0.037, p<0.0001 for low, medium and high levels of infestation, respectively) had higher MEI than individuals from houses without indoor Aedes., The MEI was driven by individual characteristics, such as gender, age and occupation/behaviors, and varied according to climatic, seasonal factors and vector control intervention (p<0.05). Nevertheless, the study did not demonstrate a clear correlation between MEI and the presence of DENV-infected Aedes. Conclusion This study represents an important step toward the validation of the specific IgG response to the Aedes salivary peptide Nterm-34kDa as a proxy measure for Aedes infestation levels and human-mosquito exposure risk in a dengue endemic setting. The use of the IgG response to the Nterm-34 kDa peptide as a viable diagnostic tool for estimating dengue transmission requires further investigations and validation in other geographical and transmission settings.