The challenge of invasive mosquito vectors in the U.K. during 2016-2018: a summary of the surveillance and control of Aedes albopictus

A difference in larval mosquito size allows a biocontrol agent to target the invasive species

As the global temperature rises in the coming decades, Aedes albopictus is expected to invade and establish in South East England, where Culex pipiens is currently the most common native mosquito species. Biocontrol measures that use local cyclopoid copepods against Ae. albopictus may be compromised if the copepods prefer alternate Cx. pipiens prey. In this study, I assessed the predation efficiency of Megacyclops viridis copepods against Ae. albopictus larvae from France and larvae that hatched from egg rafts of Cx. pipiens collected in South East England. The experiments were conducted at 15 and 25°C, which are representative of present and future summer temperatures in South East England. Ae. albopictus larvae that survived the course of the experiment in the predator-absent controls were significantly smaller than Cx. pipiens larvae that survived in the absence of predation. The background mortality of Cx. pipiens larvae increased with the 10-degree increase in temperature, and the smaller size of surviving Cx. pipiens larvae at 25°C, relative to survivors at 15°C, suggests that larger Cx. pipiens larvae were more likely to die at the higher temperature setting. Across all experimental treatments, the ratio of copepod body length to mean prey length, based on larval lengths of survivors from the corresponding predator-absent controls, was a significant predictor of the copepod's predation efficiency. Adding temperature setting to the predation efficiency model as a predictor did not improve model fit. Within the mixed prey treatments, the predation efficiency of M. viridis was 34.5 percentage points higher against Ae. albopictus prey than against Cx. pipiens prey. The higher predation efficiency that M. viridis exhibited against invasive Ae. albopictus prey, likely due to the smaller size of these larvae, supports the future use of M. viridis as a biocontrol agent in the United Kingdom.

The long-distance relationship between Dirofilaria and the UK: case report and literature review

Over the last two decades, vector-borne pathogens (VBPs) have changed their distribution across the globe as a consequence of a variety of environmental, socioeconomic and geopolitical factors. Dirofilaria immitis and Dirofilaria repens are perfect exemplars of European VBPs of One Health concern that have undergone profound changes in their distribution, with new hotspots of infection appearing in previously non-endemic countries. Some areas, such as the United Kingdom, are still considered non-endemic. However, a combination of climate change and the potential spread of invasive mosquito species may change this scenario, exposing the country to the risk of outbreaks of filarial infections. Only a limited number of non-autochthonous cases have been recorded in the United Kingdom to date. These infections remain a diagnostic challenge for clinicians unfamiliar with these "exotic" parasites, which in turn complicates the approach to treatment and management. Therefore, this review aims to (i) describe the first case of D. repens infection in a dog currently resident in Scotland, (ii) summarise the available literature on Dirofilaria spp. infections in both humans and animals in the United Kingdom and (iii) assess the suitability of the United Kingdom for the establishment of these new VBPs.

Entomological Surveillance of the Invasive Aedes Species at Higher-Priority Entry Points in Northern Iran: Exploratory Report on a Field Study

Background

Arboviral diseases such as dengue, Zika, and chikungunya are transmitted by Aedes aegypti and Ae albopictus and are emerging global public health concerns.

Objective

This study aimed to provide up-to-date data on the occurrence of the invasive Aedes species in a given area as this is essential for planning and implementing timely control strategies.

Methods

Entomological surveillance was planned and carried out monthly from May 2018 to December 2019 at higher-priority entry points in Guilan Province, Northern Iran, using ovitraps, larval collection, and human-baited traps. Species richness (R), Simpson (D), evenness (E), and Shannon-Wiener indexes (H̕) were measured to better understand the diversity of the Aedes species. The Spearman correlation coefficient and regression models were used for data analysis.

Results

We collected a total of 3964 mosquito samples including 17.20% (682/3964) belonging to the Aedes species, from 3 genera and 13 species, and morphologically identified them from May 2018 to December 2019. Ae vexans and Ae geniculatus, which showed a peak in activity levels and population in October (226/564, 40.07% and 26/103, 25.2%), were the eudominant species (D=75.7%; D=21.2%) with constant (C=100) and frequent (C=66.7%) distributions, respectively. The population of Ae vexans had a significant positive correlation with precipitation (r=0.521; P=.009) and relative humidity (r=0.510; P=.01), whereas it was inversely associated with temperature (r=−0.432; P=.04). The Shannon-Wiener Index was up to 0.84 and 1.04 in the city of Rasht and in July, respectively. The rarefaction curve showed sufficiency in sampling efforts by reaching the asymptotic line at all spatial and temporal scales, except in Rasht and in October.

Conclusions

Although no specimens of the Ae aegypti and Ae albopictus species were collected, this surveillance provides a better understanding of the native Aedes species in the northern regions of Iran. These data will assist the health system in future arbovirus research, and in the implementation of effective vector control and prevention strategies, should Ae aegypti and Ae albopictus be found in the province.

From a long-distance threat to the invasion front: a review of the invasive Aedes mosquito species in Belgium between 2007 and 2020

Invasive mosquito species (IMS) and their associated mosquito-borne diseases are emerging in Europe. In Belgium, the first detection of Aedes albopictus (Skuse 1894) occurred in 2000 and of Aedes japonicus japonicus (Theobald 1901) in 2002. Early detection and control of these IMS at points of entry (PoEs) are of paramount importance to slow down any possible establishment. This article reviews the introductions and establishments recorded of three IMS in Belgium based on published (2007–2014) and unpublished (2015–2020) data collected during several surveillance projects. In total, 52 PoEs were monitored at least once for the presence of IMS between 2007 and 2020. These included used tyre and lucky bamboo import companies, airports, ports, parking lots along highways, shelters for imported cutting plants, wholesale markets, industrial areas, recycling areas, cemeteries and an allotment garden at the country border with colonised areas. In general, monitoring was performed between April and November. Mosquitoes were captured with adult and oviposition traps as well as by larval sampling. Aedes albopictus was detected at ten PoEs, Ae. japonicus at three PoEs and Aedes koreicus (Edwards 1917) at two PoEs. The latter two species have established overwintering populations. The percentage of PoEs positive for Ae. albopictus increased significantly over years. Aedes albopictus is currently entering Belgium through lucky bamboo and used tyre trade and passive ground transport, while Ae. japonicus through used tyre trade and probably passive ground transport. In Belgium, the import through passive ground transport was first recorded in 2018 and its importance seems to be growing. Belgium is currently at the invasion front of Ae. albopictus and Ae. japonicus. The surveillance and control management actions at well-known PoEs associated to long-distance introductions are more straightforward than at less-defined PoEs associated with short-distance introductions from colonised areas. These latter PoEs represent a new challenge for IMS management in Belgium in the coming years. Aedes albopictus is expected to become established in Belgium in the coming years, hence increasing the likelihood of local arbovirus transmission. The implementation of a sustainable, structured and long-term IMS management programme, integrating active and passive entomological surveillance, vector control and Public Health surveillance is therefore pivotal.

A human-blood-derived microRNA facilitates flavivirus infection in fed mosquitoes

Hematophagous arthropods, such as mosquitoes, naturally carry and transmit hundreds of arboviruses to humans. Blood meal is a predominant physical interface that shapes cross-species communications among humans, bloodsuckers, and arboviruses. Here, we identify a human-blood-derived microRNA, hsa-miR-150-5p, that interferes with a mosquito antiviral system to facilitate flavivirus infection and transmission. hsa-miR-150-5p is acquired with a blood meal into the mosquito hemocoel and persists for a prolonged time there. The agomir of hsa-miR-150-5p enhances, whereas the antagomir represses flaviviral infection in mosquitoes and transmission from mice to mosquitoes. Mechanistic studies indicate that hsa-miR-150-5p hijacks the mosquito Argonaute-1-mediated RNA interference system to suppress the expression of some chymotrypsins with potent virucidal activity. Mosquito chymotrypsins are essential for resisting systemic flavivirus infection in hemocoel tissues. Chymotrypsin homologs potentially targeted by miR-150-5p are also found in other hematophagous arthropods, demonstrating a conserved miR-150-5p-mediated cross-species RNAi mechanism that might determine flaviviral transmissibility in nature.

Wide and increasing suitability for Aedes albopictus in Europe is congruent across distribution models

The Asian tiger mosquito (Aedes albopictus), a vector of dengue, Zika and other diseases, was introduced in Europe in the 1970s, where it is still widening its range. Spurred by public health concerns, several studies have delivered predictions of the current and future distribution of the species for this region, often with differing results. We provide the first joint analysis of these predictions, to identify consensus hotspots of high and low suitability, as well as areas with high uncertainty. The analysis focused on current and future climate conditions and was carried out for the whole of Europe and for 65 major urban areas. High consensus on current suitability was found for the northwest of the Iberian Peninsula, southern France, Italy and the coastline between the western Balkans and Greece. Most models also agree on a substantial future expansion of suitable areas into northern and eastern Europe. About 83% of urban areas are expected to become suitable in the future, in contrast with ~ 49% nowadays. Our findings show that previous research is congruent in identifying wide suitable areas for Aedes albopictus across Europe and in the need to effectively account for climate change in managing and preventing its future spread.

Potential for online crowdsourced biological recording data to complement surveillance for arthropod vectors

Voluntary contributions by citizen scientists can gather large datasets covering wide geographical areas, and are increasingly utilized by researchers for multiple applications, including arthropod vector surveillance. Online platforms such as iNaturalist accumulate crowdsourced biological observations from around the world and these data could also be useful for monitoring vectors. The aim of this study was to explore the availability of observations of important vector taxa on the iNaturalist platform and examine the utility of these data to complement existing vector surveillance activities. Of ten vector taxa investigated, records were most numerous for mosquitoes (Culicidae; 23,018 records, 222 species) and ticks (Ixodida; 16,214 records, 87 species), with most data from 2019–2020. Case studies were performed to assess whether images associated with records were of sufficient quality to identify species and compare iNaturalist observations of vector species to the known situation at the state, national and regional level based on existing published data. Firstly, tick data collected at the national (United Kingdom) or state (Minnesota, USA) level were sufficient to determine seasonal occurrence and distribution patterns of important tick species, and were able to corroborate and complement known trends in tick distribution. Importantly, tick species with expanding distributions (Haemaphysalis punctata in the UK, and Amblyomma americanum in Minnesota) were also detected. Secondly, using iNaturalist data to monitor expanding tick species in Europe (Hyalomma spp.) and the USA (Haemaphysalis longicornis), and invasive Aedes mosquitoes in Europe, showed potential for tracking these species within their known range as well as identifying possible areas of expansion. Despite known limitations associated with crowdsourced data, this study shows that iNaturalist can be a valuable source of information on vector distribution and seasonality that could be used to supplement existing vector surveillance data, especially at a time when many surveillance programs may have been interrupted by COVID-19 restrictions.

Low temperature tolerance of three Aedes albopictus strains (Diptera: Culicidae) under constant and fluctuating temperature scenarios

Background

Aedes albopictus, a vector of numerous viruses and filarial worms, has already established in 20 countries in Europe, mainly colonising subtropical regions. Continuing adaptation to climatic conditions in temperate areas would probably result in a spread to more northern European countries, producing an increasing risk of mosquito-borne pathogen transmission over a much greater area. Based on previous studies showing that Ae. albopictus is able to overwinter in Germany, this study aims to determine more exactly its ecological limits of enduring low temperatures.

Methods

Non-diapausing and experimentally induced diapausing eggs of three different Ae. albopictus strains (tropical, subtropical and temperate origins) were exposed to four different regimes with constant temperatures and three different regimes with fluctuating temperatures in a course of a day for a minimum of 2 and a maximum of 30 days. The hatching rate of larvae after cold exposure of the eggs was taken as a measure of cold tolerance.

Results

The experiments showed that the tropical Ae. albopictus strain had a lower cold tolerance than the subtropical and the temperate strains. The eggs of all used strains were able to survive constant temperatures as low as −5 °C for an exposure period of 30 days, while constant temperatures as low as −10 °C were endured for 2 days by the tropical strain and for 10 and 20 days by the subtropical and temperate strains, respectively. At fluctuating temperatures, both the subtropical and the temperate strains exhibited hatching under all temperature regimes, even with a minimum temperature of −10 °C, whereas the tropical strain ceased hatching after an exposure period of 30 days under the temperature regime with a minimum temperature of −10 °C. The analyses showed that the temperature played the major role in interpreting the hatching rates of the eggs. The condition, whether the eggs were diapausing or not, had no significant influence, although results indicated a slightly higher cold tolerance of diapausing eggs at −10 °C.

Conclusions

It must be expected that subtropical and temperate strains of Ae. albopictus are able to withstand common central European winters and are able to establish in considerable parts of the continent.

Working towards a Co-Ordinated Approach to Invasive Mosquito Detection, Response and Control in the UK

The United Kingdom (UK) has reported a single detection of the eggs of the invasive mosquito vector Aedes albopictus in each of the three years from 2016 to 2018, all in southeast England. Here, we report the detection of mosquito eggs on three occasions at two sites in London and southeast England in September 2019. Mosquito traps were deployed at 56 sites, in England, Scotland, Wales, and Northern Ireland, as part of a coordinated surveillance programme with local authorities, Edge Hill University, and government departments. Response to each detection was coordinated by Public Health England’s (PHE) local health protection teams, with technical support from PHE’s Medical Entomology group, and control conducted by the respective local authority. Control, including source reduction and larviciding, was conducted within a 300 metre radius of the positive site. The response followed a National Contingency Plan for Invasive Mosquitoes: Detection of Incursions. Although the response to these incidents was rapid and well co-ordinated, recommendations are made to further develop mosquito surveillance and control capability for the UK.

Detection of Exotic Mosquito Species (Diptera: Culicidae) at International Airports in Europe

In Europe, the air-borne accidental introduction of exotic mosquito species (EMS) has been demonstrated using mosquito surveillance schemes at Schiphol International Airport (Amsterdam, The Netherlands). Based upon these findings and given the increasing volume of air transport movements per year, the establishment of EMS after introduction via aircraft is being considered a potential risk. Here we present the airport surveillance results performed by the Centre for Monitoring of Vectors of the Netherlands, by the Monitoring of Exotic Mosquitoes (MEMO) project in Belgium, and by the Public Health England project on invasive mosquito surveillance. The findings of our study demonstrate the aircraft mediated transport of EMS into Europe from a wide range of possible areas in the world. Results show accidental introductions of Aedes aegypti and Ae. albopictus, as well as exotic Anopheles and Mansonia specimens. The findings of Ae. albopictus at Schiphol airport are the first evidence of accidental introduction of the species using this pathway in Europe. Furthermore, our results stress the importance of the use of molecular tools to validate the morphology-based species identifications. We recommend monitoring of EMS at airports with special attention to locations with a high movement of cargo and passengers.

A bacterium against the tiger: preliminary evidence of fertility reduction after release of Aedes albopictus males with manipulated Wolbachia infection in an Italian urban area

BACKGROUND

Novel tools are needed to reduce the nuisance and risk of exotic arbovirus transmission associated with the colonization of temperate regions by Aedes albopictus. The incompatible insect technique (IIT) is a population suppression approach based on cytoplasmic incompatibility between males with manipulated endosymbionts and wild females. Here, we present the results of the first field experiment in Europe to assess the capacity of an Ae. albopictus line (ARwP) deprived of its natural endosymbiont Wolbachia and transinfected with a Wolbachia strain from the mosquito Culex pipiens, to sterilize wild females.

RESULTS

We released ∼ 4500 ARwP males weekly for 6 weeks in a green area within urban Rome (Italy) and carried out egg (N = 13 442), female (N = 128) and male (N = 352) collections. Egg (N = 13 783) and female (N = 48) collections were also carried out at two untreated control sites. The percentage of viable eggs during release was, on average, significantly lower in treated sites than in control sites, with the greatest difference (16%) seen after the fourth release. The ARwP to wild male ratio in the release spots between day 3 after the first ARwP male release and day 7 after the last release was, on average, 7:10. Released males survived up to 2 weeks. Approximately 30% of females collected in the release spots showed 100% sterility and 20% showed strongly reduced fertility compared with control sites.

CONCLUSIONS

Results support the potential of IIT as a tool contributing to Ae. albopictus control in the urban context, and stress the need for larger field trials to evaluate the cost-efficacy of the approach in suppressing wild populations. © 2019 Society of Chemical Industry.

Emerging Threats to Animals in the United Kingdom by Arthropod-Borne Diseases

Worldwide, arthropod-borne disease transmission represents one of the greatest threats to public and animal health. For the British Isles, an island group on the north-western coast of continental Europe consisting of the United Kingdom (UK) and the Republic of Ireland, physical separation offers a barrier to the introduction of many of the pathogens that affect animals on the rest of the continent. Added to this are strict biosecurity rules at ports of entry and the depauperate vector biodiversity found on the islands. Nevertheless, there are some indigenous arthropod-borne pathogens that cause sporadic outbreaks, such as the tick-borne louping ill virus, found almost exclusively in the British Isles, and a range of piroplasmid infections that are poorly characterized. These provide an ongoing source of infection whose emergence can be unpredictable. In addition, the risk remains for future introductions of both exotic vectors and the pathogens they harbor, and can transmit. Current factors that are driving the increases of both disease transmission and the risk of emergence include marked changes to the climate in the British Isles that have increased summer and winter temperatures, and extended the period over which arthropods are active. There have also been dramatic increases in the distribution of mosquito-borne diseases, such as West Nile and Usutu viruses in mainland Europe that are making the introduction of these pathogens through bird migration increasingly feasible. In addition, the establishment of midge-borne bluetongue virus in the near continent has increased the risk of wind-borne introduction of infected midges and the inadvertent importation of infected cattle. Arguably the greatest risk is associated with the continual increase in the movement of people, pets and trade into the UK. This, in particular, is driving the introduction of invasive arthropod species that either bring disease-causing pathogens, or are known competent vectors, that increase the risk of disease transmission if introduced. The following review documents the current pathogen threats to animals transmitted by mosquitoes, ticks and midges. This includes both indigenous and exotic pathogens to the UK. In the case of exotic pathogens, the pathway and risk of introduction are also discussed.