The transmission ecology of Tahyna orthobunyavirus in Austria as revealed by longitudinal mosquito sampling and blood meal analysis in floodplain habitats

Background Tahyna orthobunyavirus (TAHV) is a mosquito-borne virus that may cause mild flu-like symptoms or neurological symptoms in humans. It is historically associated with floodplain habitats in Central Europe, and the mammalophilic floodwater mosquito, Aedes vexans, is thought to be the principal vector. There are few contemporary reports of TAHV transmission ecology within mosquitoes or their vertebrate hosts, and virus infections are rarely reported (and probably seldom diagnosed). The objectives of this study were to survey the mosquito population for TAHV in three floodwater habitats and describe host usage by the predominant floodwater mosquito species to potentially define TAHV transmission at these foci. Methods We performed longitudinal mosquito sampling along three major rivers in eastern Austria to characterize the mosquito community in floodplain habitats, and tested for the presence of TAHV in pools of mosquitoes. We characterized TAHV rescued from mosquito pool homogenate by sequencing. We surveyed mosquito host selection by analyzing mosquito blood meals. Results We identified TAHV in two pools of Ae. vexans captured along the Leitha River. This mosquito, and other floodwater mosquitoes, used large mammals (red deer, roe deer, wild boar) as their hosts. The sequence of the rescued virus was remarkably similar to other TAHV isolates from the region, dating back to the first isolate of TAHV in 1958. Conclusions In general, we confirmed that TAHV is most likely being transmitted by Ae. vexans, although the precise contribution of vertebrate-amplifying hosts to the ecological maintenance of the virus is unclear. The pattern of host selection matches the estimated exposure of the same large mammal species in the region to TAHV based on a recent serosurvey, but hares were also hosts at the site where TAHV was detected. We also confirm humans as hosts of two floodwater mosquito species, providing a potential mechanism for spillover of TAHV or other mosquito-borne viruses. Graphical Abstract

Use of anti-gSG6-P1 IgG as a serological biomarker to assess temporal exposure to Anopheles’ mosquito bites in Lower Moshi

Background Malaria prevalence in the highlands of Northern Tanzania is currently below 1% making this an elimination prone setting. As climate changes may facilitate increasing distribution of Anopheles mosquitoes in such settings, there is a need to monitor changes in risks of exposure to ensure that established control tools meet the required needs. This study explored the use of human antibodies against gambiae salivary gland protein 6 peptide 1 (gSG6-P1) as a biomarker of Anopheles exposure and assessed temporal exposure to mosquito bites in populations living in Lower Moshi, Northern Tanzania. Methods Three cross-sectional surveys were conducted in 2019: during the dry season in March, at the end of the rainy season in June and during the dry season in September. Blood samples were collected from enrolled participants and analysed for the presence of anti-gSG6-P1 IgG. Mosquitoes were sampled from 10% of the participants’ households, quantified and identified to species level. Possible associations between gSG6-P1 seroprevalence and participants’ characteristics were determined. Results The total number of Anopheles mosquitoes collected was highest during the rainy season (n = 1364) when compared to the two dry seasons (n = 360 and n = 1075, respectively). The gSG6-P1 seroprevalence increased from 18.8% during the dry season to 25.0% during the rainy season (χ2 = 2.66; p = 0.103) followed by a significant decline to 11.0% during the next dry season (χ2 = 12.56; p = 0.001). The largest number of mosquitoes were collected in one village (Oria), but the seroprevalence was significantly lower among the residents as compared to the rest of the villages (p = 0.039), explained by Oria having the highest number of participants owning and using bed nets. Both individual and household gSG6-P1 IgG levels had no correlation with numbers of Anopheles mosquitoes collected. Conclusion Anti-gSG6-P1 IgG is a potential tool in detecting and distinguishing temporal and spatial variations in exposure to Anopheles mosquito bites in settings of extremely low malaria transmission where entomological tools may be obsolete. However studies with larger sample size and extensive mosquito sampling are warranted to further explore the association between this serological marker and abundance of Anopheles mosquito.

The Comparative Effectiveness of Adult Mosquito Sampling Methods Dealing With Odor-baited Resting Box Traps in a Malaria-endemic Area in Southern Iran

BackgroundIran is under threat of a potential outbreak of mosquito-borne diseases, such as malaria, Dengue fever, Chikungunya, and Zika. The study aimed to determine the efficiency and sustainability of some adult mosquito sampling methods for designing effective entomological surveillance systems in a malaria endemic area.MethodsDifferent rates of tap water, sugar, and yeast (Saccharomyces cerevisiae) were mixed to provide CO2. Anopheles stephensi and Culex pipiens Bandar Abbas strains were reared in the insectary and used for tests. On a lab scale, CO2 orientation experiments were performed using a Y-tube olfactometer on the insectary mosquito strains. In the field trial, human landing catches (HLC), artificial pit shelter (APS), CO2-baited trap (CO2-BT), human and cow odor baited resting boxes (HOBT, COBT), cow urine baited trap (CUBT), and colored un-baited box (UB) were studied in Bandar Abbas, Hormozgan Province, south of Iran. Mean densities of An. stephensi and Cx. pipiens insectary strains, which oriented to CO2 as flowrate of 170, and 300 mL/minute was significantly higher compared to the control group (P < 0.05). The black un-baited inbox resting traps significantly more collected wild mosquito species compared to others colored UB (P ˂ 0.05). ResultsA total of 2722 collected mosquitoes comprises Culex pipiens (48.56%), Anopheles fluviatilis s.l.(14.21%), An. stephensi (11.68%), Cx. theileri (9.95%), Aedes caspius (7.01%), An. dthali (6.79%) An. culicifacies s.l. , An. pulcherrimus, An. sergentii,An. superpictus s.l., Cx. sitiens and, Ae.caspius less than 1%. Anopheles stephensi and, An.sergenti were most collected in CUBT. Anopheles fluviatilis s.l. and Ae. caspius were most found in HLC. Anopheles dthali, Cx. pipiens and, Cx. theileri were most abundant in APS. ConclusionsBlack CUBT and APS methods can be suggested as a perfect sampling strategy for malaria vectors surveillance. APS, and HLC methods were found useful to entomological surveillance systems for arboviral and filarial vector-borne diseases. Further modified sampling methods should be devoted to identify more effective sampling methods.

The Comparative Effectiveness of Adult Mosquito Sampling Methods Dealing With Odor-Baited Resting Box Traps in A Malaria-Endemic Area in Southern Iran

Background Iran is under threat of a potential outbreak of mosquito-borne diseases, such as malaria, Dengue fever, Chikungunya, and Zika. The study aimed to determine the efficiency and sustainability of some adult mosquito sampling methods for designing effective entomological surveillance systems in a malaria endemic area. Methods Different rates of tap water, sugar, and yeast (Saccharomyces cerevisiae) were mixed to provide CO2. Anopheles stephensi and Culex pipiens Bandar Abbas strains were reared in the insectary and used for tests. On a lab scale, CO2 orientation experiments were performed using a Y-tube olfactometer on the insectary mosquito strains. In the field trial, human landing catches (HLC), artificial pit shelter (APS), CO2-baited trap (CO2-BT), human and cow odor baited resting boxes (HOBT, COBT), cow urine baited trap (CUBT), and colored un-baited box (UB) were studied in Bandar Abbas, Hormozgan Province, south of Iran. Mean densities of An. stephensi and Cx. pipiens insectary strains, which oriented to CO2 as flowrate of 170, and 300 mL/minute was significantly higher compared to the control group (P < 0.05). The black un-baited inbox resting traps significantly more collected wild mosquito species compared to others colored UB (P ˂ 0.05). Results A total of 2722 collected mosquitoes comprises Culex pipiens (48.56%), Anopheles fluviatilis s.l.(14.21%), An. stephensi (11.68%), Cx. theileri (9.95%), Aedes caspius (7.01%), An. dthali (6.79%) An. culicifacies s.l., An. pulcherrimus, An. sergentii,An. superpictus s.l., Cx. sitiens and, Ae.caspius less than 1%. Anopheles stephensi and, An.sergenti were most collected in CUBT. Anopheles fluviatilis s.l. and Ae. caspius were most found in HLC. Anopheles dthali, Cx. pipiens and, Cx. theileri were most abundant in APS. Conclusions Black CUBT and APS methods can be suggested as a perfect sampling strategy for malaria vectors surveillance. APS, and HLC methods were found useful to entomological surveillance systems for arboviral and filarial vector-borne diseases. Further modified sampling methods should be devoted to identify more effective sampling methods.

Mosquito blood-feeding patterns and nesting behavior of American crows, an amplifying host of West Nile virus

Background Although American crows are a key indicator species for West Nile virus (WNV) and mount among the highest viremias reported for any host, the importance of crows in the WNV transmission cycle has been called into question because of their consistent underrepresentation in studies of Culex blood meal sources. Here, we test the hypothesis that this apparent underrepresentation could be due, in part, to underrepresentation of crow nesting habitat from mosquito sampling designs. Specifically, we examine how the likelihood of a crow blood meal changes with distance to and timing of active crow nests in a Davis, California, population. Methods Sixty artificial mosquito resting sites were deployed from May to September 2014 in varying proximity to known crow nesting sites, and Culex blood meal hosts were identified by DNA barcoding. Genotypes from crow blood meals and local crows (72 nestlings from 30 broods and 389 local breeders and helpers) were used to match mosquito blood meals to specific local crows. Results Among the 297 identified Culex blood meals, 20 (6.7%) were attributable to crows. The mean percentage of blood meals of crow origin was 19% in the nesting period (1 May–18 June 2014), but 0% in the weeks after fledging (19 June–1 September 2014), and the likelihood of a crow blood meal increased with proximity to an active nest: the odds that crows hosted a Culex blood meal were 38.07 times greater within 10 m of an active nest than > 10 m from an active nest. Nine of ten crow blood meals that could be matched to a genotype of a specific crow belonged to either nestlings in these nests or their mothers. Six of the seven genotypes that could not be attributed to sampled birds belonged to females, a sex bias likely due to mosquitoes targeting incubating or brooding females. Conclusion Data herein indicate that breeding crows serve as hosts for Culex in the initial stages of the WNV spring enzootic cycle. Given their high viremia, infected crows could thereby contribute to the re-initiation and early amplification of the virus, increasing its availability as mosquitoes shift to other moderately competent later-breeding avian hosts.

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.

Efficient Monitoring of Adult and Immature Mosquitoes Through Metabarcoding of Bulk Samples: A Case Study for Non-Model Culicids With Unique Ecologies

The rapid and economical monitoring of mosquitos is imperative to understanding the dynamics of both disease vectors and nuisance species. In light of technological advances in mosquito sampling and DNA sequencing, health agencies can now utilize the full potential of metabarcoding pipelines for rapid and standardizable surveillance. Here, we describe mosquito spatial and temporal variation, with particular focus on Mansonia Blanchard species, in the Madeira (Rondônia State) and the Ribeira (São Paulo) watersheds, Brazil using metabarcoding of the D2 rDNA marker. Sampling and molecular pipelines were used to evaluate the taxonomic contribution of mosquitos in pools of culicids collected en masse from macrophyte-roots (immatures) and from Mosquito Magnet traps and protected human landings (adults). Results for adult captures are comparable to morphological diagnoses and clarify previously unknown temporal and spatial species turnover. Metabarcoding of immature stages also confirmed the extent of the geographical distribution of some species and each taxon’s association with macrophyte species. Given the benefits of metabarcoding, such as taxonomic acuity, high throughput processing, and objectivity, we suggest such techniques should be more fully incorporated into culicid monitoring schemes. The metabarcoding protocol described herein paired with standardized field sampling schemes, when used by mosquito monitoring professionals, offers substantial improvements in terms of practicality, speed and cost.

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

The authors have withdrawn this preprint due to author disagreement.

Improved spatial ecological sampling using open data and standardization: an example from malaria mosquito surveillance

Vector-borne disease control relies on efficient vector surveillance, mostly carried out using traps whose number and locations are often determined by expert opinion rather than a rigorous quantitative sampling design. In this work we propose a framework for ecological sampling design which in its preliminary stages can take into account environmental conditions obtained from open data (i.e. remote sensing and meteorological stations) not necessarily designed for ecological analysis. These environmental data are used to delimit the area into ecologically homogeneous strata. By employing Bayesian statistics within a model-based sampling design, the traps are deployed among the strata using a mixture of random and grid locations which allows balancing predictions and model-fitting accuracies. Sample sizes and the effect of ecological strata on sample sizes are estimated from previous mosquito sampling campaigns open data. Notably, we found that a configuration of 30 locations with four households each (120 samples) will have a similar accuracy in the predictions of mosquito abundance as 200 random samples. In addition, we show that random sampling independently from ecological strata, produces biased estimates of the mosquito abundance. Finally, we propose standardizing reporting of sampling designs to allow transparency and repetition/re-use in subsequent sampling campaigns.

Assessing the Presence of Wuchereria bancrofti Infections in Vectors Using Xenomonitoring in Lymphatic Filariasis Endemic Districts in Ghana

Mass drug administration (MDA) is the current mainstay to interrupt the transmission of lymphatic filariasis. To monitor whether MDA is effective and transmission of lymphatic filariasis indeed has been interrupted, rigorous surveillance is required. Assessment of transmission by programme managers is usually done via serology. New research suggests that xenomonitoring holds promise for determining the success of lymphatic filariasis interventions. The objective of this study was to assess Wuchereria bancrofti infection in mosquitoes as a post-MDA surveillance tool using xenomonitoring. The study was carried out in four districts of Ghana; Ahanta West, Mpohor, Kassena Nankana West and Bongo. A suite of mosquito sampling methods was employed, including human landing collections, pyrethrum spray catches and window exit traps. Infection of W. bancrofti in mosquitoes was determined using dissection, conventional and real-time polymerase chain reaction and loop mediated isothermal amplification assays. Aedes, Anopheles coustani, An. gambiae, An. pharoensis, Culex and Mansonia mosquitoes were sampled in each of the four study districts. The dissected mosquitoes were positive for filarial infection using molecular assays. Dissected An. melas mosquitoes from Ahanta West district were the only species found positive for filarial parasites. We conclude that whilst samples extracted with Trizol reagent did not show any positives, molecular methods should still be considered for monitoring and surveillance of lymphatic filariasis transmission.