Entomological Investigation Following a Zika Outbreak in Brownsville, Texas

ABSTRACT In November and December 2016, an outbreak of locally transmitted Zika occurred in Brownsville, TX. The Texas Department of State Health Services requested for a Centers for Disease Control and Prevention (CDC) Epi Aid, and as part of that Epi Aid a team of CDC entomologists was deployed in January 2017. The mission was to improve mosquito-based arbovirus surveillance and evaluate the possibility of continuing local Zika virus (ZIKV) transmission in the city. The mosquito-based arbovirus surveillance program was expanded from 4 to 40 BG-Sentinel traps evenly distributed throughout the city. Over a 2-wk period, 15 mosquito species were detected; the most abundant species were Culex quinquefasciatus, Aedes aegypti, and Ae. albopictus, which accounted for 66.7%, 16.2%, and 5.7% of the total mosquito collection, respectively. The relative abundance of Ae. aegypti (1.0 mosquitoes/trap/day) and Ae. albopictus (0.4 mosquitoes/trap/day) was very low and unlikely to initiate and/or sustain ZIKV transmission. Zika virus was not detected in the mosquitoes collected, suggesting no or extremely low ZIKV transmission at that time.

The invasive Korean bush mosquito Aedes koreicus (Diptera: Culicidae) in Germany as of 2020

Background The Korean bush mosquito Aedes koreicus was recently reported to have established a population in western Germany (Wiesbaden) in 2016. The species is difficult to distinguish morphologically from its close relative, the invasive Japanese bush mosquito Ae. japonicus, which is already widely distributed in many parts of Germany, including the area colonised by Ae. koreicus. Genetic confirmation of morphologically identified “Ae. japonicus” collection material, however, had only been done exceptionally before the German Ae. koreicus population became known. Methods Dried archived “Ae. japonicus” specimens both from the municipality of Wiesbaden and from deliberately and randomly selected distribution sites all over Germany were re-examined morphologically and genetically for admixture by Ae. koreicus. Moreover, cemeteries in the greater Wiesbaden area were sampled in 2019 and 2020 to check for Ae. koreicus spread. Korean and Japanese bush mosquitoes submitted to the German citizen science mosquito monitoring scheme “Mueckenatlas” in 2019 and 2020 were also subjected to particularly thorough species identification. The ND4 DNA sequences generated in this study in the context of species identification were phylogenetically compared to respective GenBank entries of Ae. koreicus. As a by-product, several genetic markers were evaluated for their suitability to identify Ae. koreicus. Results Aedes koreicus specimens could be identified in mosquito collection material and submissions from Wiesbaden from 2015 onwards, suggesting establishment to have happened in the same year as Ae. japonicus establishment. Detections of Ae. koreicus from 2019 and 2020 in Wiesbaden indicate a negligible enlargement of the populated area as described for 2018. Two Ae. koreicus specimens were also submitted from the city of Munich, southern Germany, in 2019 but further specimens could not be identified during immediate local inspections. Comparison of ND4 sequences generated in this and other studies demonstrate a high degree of homology, suggesting that this DNA region is not informative enough for clarification of origins and relationships of Ae. koreicus populations. For genetic identification of Ae. koreicus, PCR primers used for classical CO1 barcoding were found to lead to mismatches and produce no or incorrect amplicons. Alternative CO1 primers or a validated ND4 marker should be used instead. Conclusions Aedes koreicus is probably introduced into Germany every now and then but rarely succeeds in becoming established. As with most European populations, the German population is characterised by a limited expansion tendency. Since Ae. koreicus is a potential vector, however, Asian bush mosquitoes found at new places should be examined quite carefully and known distribution areas of Ae. japonicus regularly checked for the presence of Ae. koreicus. Graphical Abstract

TYPES AND ABUNDANCE OF MOSQUITOES IN KAHYAPU VILLAGE, ENGGANO ISLAND, NORTHEST BENGKULU

Research has been carried out on the types and abundance of mosquitoes in Kahyapu Village, Enggano Island, Northest Bengkulu in December 2018 – May 2019 with the goals to knowing the types and abundance of mosquitoes found in Kahyapu Village, Enggano Island, Northest Bengkulu. The research location points were determined by purposive sampling and the mosquito collection at each other location point was determined using the Human Landing Collection method. The mosquitoes obtained were grouped by genus and species, the data obtained were analyzed descriptively. From the results of the study obtained 4 species of mosquitoes, namely Aedes albopictus, Armigeres subalbatus, Culex fuscocephala and Culex quinquefasciatus. mosquito with high abundance are Aedes albopictus.

Accounting for heterogeneity in wild adult samples to measure insecticide resistance in Anopheles malaria vectors

Background Systematic, long-term, and spatially representative monitoring of insecticide resistance in mosquito populations is urgently needed to quantify its impact on malaria transmission, and to combat failing interventions when resistance emerges. Resistance assays on wild-caught adult mosquitoes (known as adult-capture) offer an alternative to the current protocols, and can be done cheaply, in a shorter time frame, and in the absence of an insectary. However, quantitative assessments of the performance of these assays relative to the gold standard, which involves rearing larvae in an insectary, are lacking. Methodology/Principal findings We developed a discrete-time deterministic mosquito lifecycle model to simulate insecticide resistance assays from adult-captured mosquito collection in a heterogeneous environment compared to the gold standard larval capture methods, and to quantify possible biases in the results. We incorporated non-lethal effects of insecticide exposure that have been demonstrated in laboratory experiments, spatial structure, and the impact of multiple exposure to insecticides and natural ageing on mosquito death rates during the assay. Using output from this model, we compared the results of these assays to true resistance as measured by the presence of the resistance allele. In simulated samples of 100 test mosquitoes, reflecting WHO-recommended sample sizes, we found that compared to adult-captured assays (MSE = 0.0059), larval-captured assays were a better measure of true resistance (MSE = 0.0018). Using a correction model, we were able to improve the accuracy of the adult-captured assay results (MSE = 0.0038). Bias in the adult-capture assays was dependent on the level of insecticide resistance rather than coverage of bed nets or spatial structure. Conclusions/Significance Using adult-captured mosquitoes for resistance assays has logistical advantages over the standard larval-capture collection, and may be a more accurate sample of the mosquito population. These results show that adult-captured assays can be improved using a simple mathematical approach and used to inform resistance monitoring programs.

A global assessment of surveillance methods for dominant malaria vectors

The epidemiology of human malaria differs considerably between and within geographic regions due, in part, to variability in mosquito species behaviours. Recently, the WHO emphasised stratifying interventions using local surveillance data to reduce malaria. The usefulness of vector surveillance is entirely dependent on the biases inherent in the sampling methods deployed to monitor mosquito populations. To understand and interpret mosquito surveillance data, the frequency of use of malaria vector collection methods was analysed from a georeferenced vector dataset (> 10,000 data records), extracted from 875 manuscripts across Africa, the Americas and the Asia-Pacific region. Commonly deployed mosquito collection methods tend to target anticipated vector behaviours in a region to maximise sample size (and by default, ignoring other behaviours). Mosquito collection methods targeting both host-seeking and resting behaviours were seldomly deployed concurrently at the same site. A balanced sampling design using multiple methods would improve the understanding of the range of vector behaviours, leading to improved surveillance and more effective vector control.

AKTIVITAS NOKTURNAL Aedes spp.VEKTOR DEMAM BERDARAH DENGUE DI KOTA SEMARANG

Sendangmulyo Village is one of the DHF (Dengue Hemorrhagic Fever) endemic areas in Semarang City. Previous studies reported that Aedes spp. active biting at night (nocturnal biting activity) in some areas in Indonesia. This indicates that changes in the blood-sucking behavior of Aedes spp mosquitoes can have an impact on dengue transmission. This research is a descriptive study with a cross-sectional study design. The study was conducted in 64 houses. The mosquito field collection was carried out using the resting mosquito collection method at 18.00-06.00 WIB. Observations of environmental parameters were also carried out to determine the temperature and humidity of the environment around the breeding grounds of Aedes spp. The results showed that there was a change in Aedes spp's blood-sucking activity from 16.00-17.00 WIB to 18.00-20.00 WIB. The distribution of Aedes albopictus in Sendangmulyo Village was 18% of the total Aedes spp. mosquitoes collected with a Resting Rate (RR) value of 0.98%. The average temperature and humidity in the area were 28.6 °C and 77.2%, respectively. This change in blood-sucking activity in Aedes spp has the potential to increase the risk of spreading DHF in Sendangmulyo Village. Dengue Hemorrhagic Fever vector control efforts need to be improved. Abstrak Kelurahan Sendangmulyo merupakan salah satu daerah endemis DBD (Demam Berdarah Dengue) di Kota Semarang. Studi-studi sebelumnya melaporkan bahwa Aedes spp. aktif menggigit pada malam hari (aktivitas menggigit nokturnal) di beberapa daerah di Indonesia. Hal ini mengindikasikan adanya perubahan perilaku menghisap darah nyamuk Aedes spp. dapat berdampak pada penularan dengue. Penelitian ini merupakan penelitian deskriptif dengan desain studi cross sectional. Penelitian dilakukan pada 64 rumah. Koleksi lapangan nyamuk dilakukan dengan metode koleksi nyamuk istirahat pada pukul 18.00-06.00 WIB. Pengamatan parameter lingkungan juga dilakukan untuk mengetahui suhu dan kelembaban lingkungan disekitar tempat perkembangbiakan Aedes spp. Hasil penelitian menunjukkan adanya perubahan aktivitas menghisap darah Aedes spp dari pukul 16.00-17.00 WIB menjadi pukul 18.00-20.00 WIB. Sebaran Aedes albopictus di Kelurahan Sendangmulyo adalah 18% dari total nyamuk Aedes spp yang terkoleksi dengan nilai Resting Rate (RR) sebesar 0,98%. Rata-rata suhu dan kelembaban di daerah tersebut masing-masing adalah 28,6 °C dan 77,2%. Perubahan aktivitas menghisap darah pada Aedes spp ini berpotensi meningkatkan risiko penyebaran DBD di Kelurahan Sendangmulyo. Upaya pengendalian vektor DBD perlu ditingkatkan.

Assessment of Mosquito Collection Methods for Dengue Surveillance

Several methods exist to collect and assess the abundance of dengue vector mosquitoes, i.e., morning adult collection, pupal collection, ovitraps, human landing, and larval collection. Several of these methods are officially implemented to monitor mosquito density and make decisions on treatments for dengue control. This monitoring is also constrained by the need to conduct this assessment on a “one point/one day” process, meaning that once the threshold of 100 households is reached, the assessment is made, and the collectors teams move to another place, thus preventing the use of long-term sampling methods. This diversity of methods might be a source of variability and lack of statistical significance. There is also a lack of published data regarding the efficacy of these methods. Furthermore, the Stegomyia indices are shown to be not reliable for assessing the risk of dengue outbreaks. A mosquito survey was, thus, conducted in 39 locations corresponding to 15 dengue endemic provinces in Indonesia by using the different adult and larval collection methods recommended nationwide. A total of 44,675 mosquitoes were collected. The single larva method was the most efficient. Out of a total of 89 dengue-positive pools, the most frequently encountered virus was DENV2, which made up half of the positive samples, followed by DENV3 and DENV1, respectively. Factor analysis of mixed data showed that no correlation could be found between any methods and the presence of dengue virus in mosquitoes. Moreover, no correlation could be found between any methods and the incidence of dengue. There was no consistency in the efficacy of a given method from one site to another. There was no correlation between any of the parameters considered, i.e., method, incidence of dengue, location, and the presence of dengue virus in mosquitoes.

Eave and swarm collections prove effective for biased captures of male Anopheles gambiae mosquitoes in Uganda

Background Traditional malaria vector sampling techniques bias collections towards female mosquitoes. Comprehensive understanding of vector dynamics requires balanced vector sampling of both males and females. Male mosquito sampling is also necessary for population size estimations by male-based mark-release-recapture (MRR) studies and for developing innovations in mosquito control, such as the male-targeted sterile insect technique and other genetic modification approaches. This study evaluated a range of collection methods which show promise in providing a more equal, or even male-biased, sex representation in the sample. Results Swarms were found at all study sites and were more abundant and larger at the peak of the wet season. Swarm sampling caught the most males, but when man/hour effort was factored in, sampling of eaves by aspiration was the more efficient method and also provided a representative sample of females. Grass-roofed houses were the most productive for eave collections. Overall few mosquitoes were caught with artificial resting traps (clay pots and buckets), although these sampling methods performed better at the start of the wet season than at its peak, possibly because of changes in mosquito ecology and an increased availability of natural resting sites later in the season. Aspiration of bushes was more productive at the peak of the wet season than at the start. Conclusions The results of this study demonstrate that eave aspiration was an efficient and useful male mosquito collection method at the study sites and a potentially powerful aid for swarm location and MRR studies. The methods evaluated may together deliver more sex-balanced mosquito captures and can be used in various combinations depending on the aims and ecological parameters of a given study.

Indoor and outdoor malaria transmission in two ecological settings in rural Mali: Implications for vector control

Background: Implementation and upscale of effective malaria vector control strategies necessitates understanding the multi-factorial aspects of transmission patterns. The primary aims of this study are to determine the vector composition, biting rates, trophic preference, and the overall importance of distinguishing outdoor versus indoor malaria transmission through a study at two communities in rural Mali. Methods: Mosquito collection was carried out between July 2012 and June 2016 at two rural Mali communities (Dangassa and Koïla Bamanan) using pyrethrum spray-catch and human landing catch approaches at both indoor and outdoor locations. Species of Anopheles (An.) gambiae complex were identified by polymerase chain reaction (PCR). Enzyme-Linked -Immuno-Sorbent Assay (ELISA) were used to determine the origin of mosquito blood meals and presence of Plasmodium (P.) falciparum sporozoite infections.Results: A total of 11,237 An. gambiae (s.l.) were collected during the study period (5,239 and 5,998 from the Dangassa and Koïla Bamanan sites, respectively). Of the 679 identified by PCR in Dangassa, An. coluzzii was the predominant species with 91.4% of the catch followed by An. gambiae (8.0%) and An. arabiensis (0.6%). At the same time in Koïla Bamanan, of 623 An. gambiae s.l., An. coluzzii accounted for 99% of the catch, An. arabiensis 0.8% and An. gambiae 0.2%. Human Blood Index (HBI) measures were significantly higher in Dangassa (79.4%; 95% Bayesian credible interval (BCI) [77.4, 81.4]) than in Koïla Bamanan (15.9%; 95% BCI [14.7, 17.1]). The human biting rates were higher during the second half of the night at both sites. In Dangassa, the sporozoite rate was comparable between outdoor and indoor mosquito collections. For outdoor collections, the sporozoite positive rate was 3.6% (95% BCI [2.1-4.3]) and indoor collections were 3.1% (95% BCI [2.4-5.0]). In Koïla Bamanan, the sporozoite rate was higher indoors at 4.3% (95% BCI [2.7-6.3]) compared with outdoors at 2.4% (95% BCI [1.1- 4.2]). In Dangassa, corrected entomological inoculation rates (cEIRs) using HBI were 13.74 [95% BCI: 9.21—19.14] infective bites/person/month (ib/p/m) at indoor, and 18.66 [95% BCI 12.55—25.81] ib/p/m at outdoor. For Koïla Bamanan, cEIRs were 1.57 [95% BCI 2.34 —2.72] ib/p/m and 0.94 [95% BCI 0.43—1.64] ib/p/m for indoor and outdoor, respectively. EIRs were significantly higher at the Dangassa site than the Koïla Bamanan site.Conclusion: The findings in this work may indicate the occurrence of active, outdoor residual malaria transmission is comparable to indoor transmission in some geographic settings. The high outdoor transmission patterns observed here highlight the need for additional strategies to combat outdoor malaria transmission to complement traditional indoor preventive approaches such as long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS) which typically focus on resting mosquitoes.

Impacts of Ivermectin Mass Drug Administration for Onchocerciasis on Mosquito Populations of Ogun State, Nigeria.

Background: This study investigated the impacts of single-dose mass drug administration (MDA) with ivermectin for onchocerciasis and lymphatic filariasis on mosquito populations in Ogun State, Nigeria. Methods: Mosquito samples were collected indoor and outdoor in two communities before and after MDA. The communities were pair-matched with two other control communities where concurrent mosquito collection was also carried out. The mosquitoes were identified by morphological features and parity status was determined by microscopy. The density and age structure of the mosquitoes were determined and compared between intervention and control communities. Environmental and climatic data of study locations were obtained from online databases. MDA treatment coverage survey was conducted in the treated communities. Results: Before MDA, the density of indoor Anopheles mosquitoes was 7.20 in the control communities. This was significantly lower (p = 0.049) in the intervention communities where the density was 1.43. The density of the indoor Anopheles population reduced significantly 2-3 days after MDA to 1.02 (p = 0.039) in the intervention communities. Parity rate also reduced significantly from 95.35 to 44.26 (p < 0.001). The density of indoor Anopheles rebounded to 1.45 two weeks after MDA while parity rate remained significantly lower (p = 0.001) than before MDA. The density of indoor Culex increased 2-3 days after MDA from 0.07 to 0.10 (p = 0.527) and to 0.25 (p = 0.012) 13-14 days after MDA in the intervention communities. In Amini where MDA coverage was 65.9%, the indoor density of Anopheles reduced significantly from 0.90 to 0.33 (p = 0.005) 2-3 days after MDA while in Kugba-Ajagbe where MDA coverage was 41.0%, the reduction from 1.97 to 1.70 was not statistically significant (p = 0.446). Exposure to MDA across sampling intervals in the intervention communities showed a significant effect on the density (p < 0.001) and parity rate (p = 0.003) of indoor Anopheles in the generalized linear model examining multiple factors. Conclusion: Ivermectin MDA showed a promising potential to impact on malaria transmission and Anopheles abundance at high MDA coverage.