Comparison of four outdoor mosquito trapping methods as potential replacements for human landing catches in western Kenya

Introduction Longitudinal monitoring of outdoor-biting malaria vector populations is becoming increasingly important in understanding the dynamics of residual malaria transmission. However, the human landing catch (HLC), the gold standard for measuring human biting rates indoors and outdoors, is costly and raises ethical concerns related to increased risk of infectious bites among collectors. Consequently, routine data on outdoor-feeding mosquito populations are usually limited because of the lack of a scalable tool with similar sensitivity to outdoor HLC. Methodology The Anopheles trapping sensitivity of four baited proxy outdoor trapping methods—Furvela tent trap (FTT), host decoy trap (HDT), mosquito electrocuting traps (MET) and outdoor CDC light traps (OLT)—was assessed relative to HLC in a 5 × 5 replicated Latin square conducted over 25 nights in two villages of western Kenya. Indoor CDC light trap (ILT) was run in one house in each of the compounds with outdoor traps, while additional non-Latin square indoor and outdoor HLC collections were performed in one of the study villages. Results The MET, FTT, HDT and OLT sampled approximately 4.67, 7.58, 5.69 and 1.98 times more An. arabiensis compared to HLC, respectively, in Kakola Ombaka. Only FTT was more sensitive relative to HLC in sampling An. funestus in Kakola Ombaka (RR = 5.59, 95% CI 2.49–12.55, P < 0.001) and Masogo (RR = 4.38, 95% CI 1.62–11.80, P = 0.004) and in sampling An. arabiensis in Masogo (RR = 5.37, 95% CI 2.17–13.24, P < 0.001). OLT sampled significantly higher numbers of An. coustani in Kakola Ombaka (RR = 3.03, 95% CI 1.65–5.56, P < 0.001) and Masogo (RR = 2.88, 95% CI 1.15–7.22, P = 0.02) compared to HLC. OLT, HLC and MET sampled mostly An. coustani, FTT had similar proportions of An. funestus and An. arabiensis, while HDT sampled predominantly An. arabiensis in both villages. FTT showed close correlation with ILT in vector abundance for all three species at both collection sites. Conclusion FTT and OLT are simple, easily scalable traps and are potential replacements for HLC in outdoor sampling of Anopheles mosquitoes. However, the FTT closely mirrored indoor CDC light trap in mosquito indices and therefore may be more of an indoor mimic than a true outdoor collection tool. HDT and MET show potential for sampling outdoor host-seeking mosquitoes. However, the traps as currently designed may not be feasible for large-scale, longitudinal entomological monitoring. Therefore, the baited outdoor CDC light trap may be the most appropriate tool currently available for assessment of outdoor-biting and malaria transmission risk. Graphic abstract

Mosquito Identification From Bulk Samples Using DNA Metabarcoding: a Protocol to Support Mosquito-Borne Disease Surveillance in Canada

Approximately 80 species of mosquitoes (Diptera: Culicidae) have been documented in Canada. Exotic species such as Aedes albopictus (Skuse) (Diptera: Culicidae) are becoming established. Recently occurring endemic mosquito-borne diseases (MBD) in Canada including West-Nile virus (WNV) and Eastern Equine Encephalitis (EEE) are having significant public health impacts. Here we explore the use of DNA metabarcoding to identify mosquitoes from CDC light-trap collections from two locations in eastern Canada. Two primer pairs (BF2-BR2 and F230) were used to amplify regions of the cytochrome c oxidase subunit I (CO1) gene. High throughput sequencing was conducted using an Illumina MiSeq platform and GenBank-based species identification was applied using a QIIME 1.9 bioinformatics pipeline. From a site in southeastern Ontario, Canada, 26 CDC light trap collections of 72 to &gt;300 individual mosquitoes were used to explore the capacity of DNA metabarcoding to identify and quantify captured mosquitoes. The DNA metabarcoding method identified 33 species overall while 24 species were identified by key. Using replicates from each trap, the dried biomass needed to identify the majority of species was determined to be 76 mg (equivalent to approximately 72 mosquitoes), and at least two replicates from the dried biomass would be needed to reliably detect the majority of species in collections of 144–215 mosquitoes and three replicates would be advised for collections with &gt;215 mosquitoes. This study supports the use of DNA metabarcoding as a mosquito surveillance tool in Canada which can help identify the emergence of new mosquito-borne disease potential threats.

Evaluation of Mosquito Magnet and other collection tools for Anopheles mosquito vectors of simian malaria

Background Vector surveillance is essential in determining the geographical distribution of mosquito vectors and understanding the dynamics of malaria transmission. With the elimination of human malaria cases, knowlesi malaria cases in humans are increasing in Malaysia. This necessitates intensive vector studies using safer trapping methods which are both field efficient and able to attract the local vector populations. Thus, this study evaluated the potential of Mosquito Magnet as a collection tool for Anopheles mosquito vectors of simian malaria along with other known collection methods. Methods A randomized 4 × 4 Latin square designed experiment was conducted to compare the efficiency of the Mosquito Magnet against three other common trapping methods: human landing catch (HLC), CDC light trap and human baited trap (HBT). The experiment was conducted over six replicates where sampling within each replicate was carried out for 4 consecutive nights. An additional 4 nights of sampling was used to further evaluate the Mosquito Magnet against the “gold standard” HLC. The abundance of Anopheles sampled by different methods was compared and evaluated with focus on the Anopheles from the Leucosphyrus group, the vectors of knowlesi malaria. Results The Latin square designed experiment showed HLC caught the greatest number of Anopheles mosquitoes (n = 321) compared to the HBT (n = 87), Mosquito Magnet (n = 58) and CDC light trap (n = 13). The GLMM analysis showed that the HLC method caught significantly more Anopheles mosquitoes compared to Mosquito Magnet (P = 0.049). However, there was no significant difference in mean nightly catch of Anopheles mosquitoes between Mosquito Magnet and the other two trapping methods, HBT (P = 0.646) and CDC light traps (P = 0.197). The mean nightly catch for both An. introlatus (9.33 ± 4.341) and An. cracens (4.00 ± 2.273) caught using HLC was higher than that of Mosquito Magnet, though the differences were not statistically significant (P > 0.05). This is in contrast to the mean nightly catch of An. sinensis (15.75 ± 5.640) and An. maculatus (15.78 ± 3.479) where HLC showed significantly more mosquito catches compared to Mosquito Magnet (P < 0.05). Conclusions Mosquito Magnet has a promising ability to catch An. introlatus and An. cracens, the important vectors of knowlesi and other simian malarias in Peninsular Malaysia. The ability of Mosquito Magnet to catch some of the Anopheles mosquito species is comparable to HLC and makes it an ethical and safer alternative. Graphic Abstract

Towards Safer and More Sustainable Systems for Monitoring Exophagic Vectors of Malaria in Western Kenya

Introduction. Longitudinal monitoring of outdoor-biting malaria vector populations is becoming increasingly important in understanding the dynamics of residual malaria transmission. However, the human landing catch (HLC), the gold standard for measuring human biting rates indoors and outdoors, is costly and raises ethical concerns related to increased risk of infective bites among collectors. Consequently, routine data on outdoor-feeding mosquito populations are usually limited due to the lack of a scalable tool with similar sensitivity to outdoor HLC. Methodology. The Anopheles trapping sensitivity of four baited proxy outdoor trapping methods—Furvela tent trap (FTT), host decoy trap (HDT), mosquito electrocuting traps (MET) and outdoor CDC light traps (OLT)—was assessed relative to HLC in a 5x5 replicated Latin square conducted over 25 nights in two villages of western Kenya. Indoor CDC light trap (ILT) was run in one house in each of the compounds with outdoor traps, while additional non-Latin square indoor and outdoor HLC collections were performed in one of the study villages. Results. The MET, FTT, HDT and OLT sampled approximately 4.67, 7.58, 5.69 and 1.98 times more An. arabiensis compared to HLC, respectively, in Kakola Ombaka. Only FTT was more sensitive relative to HLC in sampling of An. funestus in Kakola Ombaka (RR=5.59, 95%CI: 2.49-12.55, P < 0.001) and Masogo (RR=4.38, 95%CI: 1.62-11.80, P = 0.004) and in sampling An. arabiensis in Masogo (RR=5.37, 95%CI: 2.17-13.24, P < 0.001). OLT sampled significantly higher numbers of An. coustani in Kakola Ombaka (RR=3.03, 95%CI: 1.65-5.56, P < 0.001) and Masogo (RR=2.88, 95%CI: 1.15-7.22, P=0.02) compared to HLC. OLT, HLC and MET sampled mostly An. coustani, FTT had similar proportions of An. funestus and An. arabiensis, while HDT sampled predominantly An. arabiensis in both villages. FTT showed close correlation with ILT in vector abundance for all three species at both collection sites. Conclusion. FTT and OLT are simple, easily scalable traps and are potential replacements for HLC in outdoor sampling of Anopheles mosquitoes. However, the FTT closely mirrored indoor CDC light trap in mosquito indices and therefore may be more of an indoor mimic than a true outdoor collection tool. HDT and MET show potential for sampling outdoor host seeking mosquitoes. However, the traps as currently designed may not be feasible for large scale, longitudinal entomological monitoring. Therefore, the baited outdoor CDC light trap may be the most appropriate tool currently available for assessment of outdoor-biting and malaria transmission risk.

COMPARISON OF THE CDC LIGHT TRAP AND THE DYNATRAP® DT2000 FOR COLLECTION OF MOSQUITOES IN SEMI-FIELD AND FIELD SETTINGS

The CDC light trap has been the standard used by mosquito control programs to conduct mosquito and arbovirus surveillance. For the last two decades, this trap has been used with little to no modifications to its original design. Recently, new traps that utilize different light sources, modified designs, and attractants have been developed and evaluated against the CDC light trap. A semi-field and field comparison of the Dynatrap® (Model DT2000) against the CDC light trap was conducted at Anastasia Mosquito Control District. The DT2000 varies from the CDC light trap with a UV light, trapdoor/fan mechanism, and Atrakta lure which is a combination of lactic acid, ammonia, and hexanoic acid. Overall, the DT2000 collected 56% (327/600) of the Ae. aegypti released in the semifield cage, compared to 18.5% (111/600) collected by the CDC light traps. These findings suggest that the DT2000 outperformed the CDC light trap in collecting Ae. aegypti. In the field, the DT2000 collected nine target mosquito species while the CDC light trap collected four target species. The DT2000 averaged 109 ± 97.46 mosquitoes and the CDC light trap averaged 8 ± 4.64 mosquitoes. The DT2000 presented functional limitations in the field as an electrical outlet was required. Study findings suggest that where an electrical outlet is available, the DT2000 may be an alternative to the CDC light trap for mosquito surveillance.

EVALUATION OF CDC LIGHT TRAP, BG SENTINEL TRAP, AND MMX TRAP FOR THE COLLECTION OF SALT MARSH MOSQUITOES IN ANASTASIA STATE PARK, SAINT AUGUSTINE, FLORIDA

Salt marsh mosquitoes are major nuisance pests during the periods of high mosquito activity, especially after major storm events. In 2016-2017, Saint John’s County, Florida, USA was struck by two major hurricanes that resulted in multiple outbreaks of salt marsh mosquito populations. To optimize the surveillance of two salt marsh mosquitoes, (Aedes taeniorhynchus and Ae. sollicitans, three types of traps (the Centers for Disease Control (CDC) Light trap, Biogents Sentinel (BG) trap and Counter Flow Geometry Model (MMX) trap were tested for their capacity to capture the highest numbers of high quality live specimens for laboratory bioassays. Each trap type was tested in Anastasia State Park, located along a major salt marsh area in Saint John’s County. Although the MMX trap captured most of the salt marsh mosquitoes collected, the numbers of mosquitoes captured was not statistically significant compared to the other trap types. However, there was a significant difference in the numbers between Ae. taeniorhynchus and Ae. sollicitans in the MMX traps. The MMX trap is preferred for capturing salt marsh mosquitoes that are in high quality for the CDC bottle bioassays.

Assessment of the Effectiveness of Various Adult Mosquito Sampling Methods in a Thickly Populated Urban Slum Settlement - A study from Besant Nagar, Chennai, India

BackgroundIn an urban scenario, it is an arduous task to collect adult Anopheles stephensi, unlike the immature forms due to various reasons such as the complex spatial heterogeneity, intricacies in feeding, and resting preferences. Thus it is necessary to have more specific and accurate assessments of adult vector density by performing various collection methods and timeframes to achieve appropriate and sustainable vector control strategies.Methods The study was undertaken in two phases, (i) resting dawn collections in cattle sheds from Jan 2015 to Dec 2016 to assess the possibility of maximum collection of An. stephensi compared to dusk collections done previously and to find out the best appropriate collection strategy for vector control and (ii) light trap collections from Jan 2016 to Apr 2017 to determine the efficiency and reliability of CDC light trap in sampling the anophelines including the urban malaria vector, Anopheles stephensi in human dwellings besides, other mosquito species. The man-hour density of An. stephensi in cattle sheds were calculated and its infection rate was analyzed by circum-sporozoite ELISA (CS-ELISA). Binary logistic regression analysis was done to ascertain the variables associated with the collection of Anopheles stephensi using a light trap.Results The resting collections in cattle sheds indicated that dawn collections yielded more Anopheles stephensi than at dusk. The resting stage female (fully fed, semi-gravid, and gravid) mosquitoes were more in dawn collections than in dusk collections. The CDC-light trap collections revealed that An. stephensi collected indoors were more than outdoor in human dwellings. Further, vector incrimination results observed that 0.56% of the female An. stephensi from cattle sheds were infected in 2014 (dusk), 0.15%, and 0.09% in 2015 and 2016 respectively in dawn collections. Nevertheless, 2.3% of An. stephensi collected by CDC light trap in human dwellings were positive for Plasmodium vivax (Pv210) infection. Binary logistic regression analysis proved that the presence of An. stephensi in human dwellings was significantly influenced by seasons, the number of rooms in the house, number of household members, and also the use of repellents.ConclusionsThe different collection (resting and light trap) approaches were assessed to find out the appropriate collection method and time which could yield the maximum number of An. stephensi with the existing resources. The study revealed that dawn collections during the early hours as the most suitable time to collect wild An. stephensi in an urban setting. The present study thus would help in chalking out an operationally feasible vector control strategy with the most appropriate methodology, timeframe useful for effective control of vectors.

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

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.

Diversitas Nyamuk di Sekitar Kandang Ternak di Kecamatan Mantikulore Kota Palu

Mosquito transmitted diseases are still a health problem in Indonesia, including in Palu City. Among the types of mosquitoes as a vector of the disease, there are to be zoophilic of animal blood. The study against the diversity of mosquitoes has been conducted in the area with the largest cattle population in Palu City, that Mantikulore District. The purpose of this study was to gain an overview diversity of mosquitoes around the cattle sheds. The study was carried out with free collection of mosquitoes around cattle sheds from 18:00 to 06:00 and one light trapping (CDC-Light Trap) at each location throughout the night from 18:00 to 06:00. Distribution diversity of mosquito around cattle sheds in five locations obtained 3 genus and 14 species of mosquitoes from a total of 1,464 captured mosquitoes. Culex vishnui is the most abundant mosquito in four research sites, namely in Kawatuna (44.44%), Poboya (82.18%), Tondo (66.95%), and Tanamodindi (38.58%). While in Talise the most abundant mosquito is Cx. quinquefasciatus amount 52.39%. The abundance of Cx. quinquefasciatus and Cx. vishnui was directly proportional to the frequency and dominance index. Shannon-Wiener diversity index shows the level of diversity in Kawatuna village, Talise village, and Tanamodindi village belongs to the medium, and in Poboya village and Tondo village belongs to low.