Field-based assessments of the seasonality of Culex pipiens sensu lato in England: an important enzootic vector of Usutu and West Nile viruses

BACKGROUND

Usutu virus (USUV), which is closely related to West Nile virus (WNV), sharing a similar ecology and transmission cycle, was first reported in the UK in the southeast of England in 2020. Both USUV and WNV are emerging zoonotic viruses hosted by wild birds. The 2020 finding of USUV in England raised awareness of this virus and highlighted the importance of understanding the seasonality of Culex pipiens sensu lato (Cx. pipiens s.l.), the main enzootic vector of these viruses. Zoos are prime locations for trapping mosquitoes because of their infrastructure, security, and range of vertebrate hosts and aquatic habitats.

METHODS

Three independent zoo-based case studies at four locations that cover the seasonality of Cx. pipiens s.l. in England were undertaken: (i) London Zoo (Zoological Society London [ZSL]) and surrounding areas, London; (ii) Chester Zoo (Cheshire); (ii) Twycross Zoo (Leicestershire); and (iv) Flamingo Land (zoo; North Yorkshire). Various adult mosquito traps were used to catch adult Cx. pipiens s.l. across seasons.

RESULTS

High yields of Cx. pipiens s.l./Culex torrentium were observed in Biogents-Mosquitaire and Center for Disease Control and Prevention Gravid traps in all studies where these traps were used. Mosquito counts varied between sites and between years. Observations of adult Cx. pipiens s.l./Cx. torrentium abundance and modelling studies demonstrated peak adult abundance between late July and early August, with active adult female Cx. pipiens s.l./Cx. torrentium populations between May and September.

CONCLUSIONS

The information collated in this study illustrates the value of multiple mosquito monitoring approaches in zoos to describe the seasonality of this UK vector across multiple sites in England and provides a framework that can be used for ongoing and future surveillance programmes and disease risk management strategies.

Ťahyňa virus-A widespread, but neglected mosquito-borne virus in Europe

Ťahyňa virus (TAHV) is an orthobunyavirus and was the first arbovirus isolated from mosquitoes in Europe and is associated with floodplain areas as a characteristic biotope, hares as reservoir hosts and the mammal-feeding mosquitoes Aedes vexans as the main vector. The disease caused by TAHV ("Valtice fever") was detected in people with acute flu-like illness in the 1960s, and later the medical significance of TAHV became the subject of many studies. Although TAHV infections are widespread, the prevalence and number of actual cases, clinical manifestations in humans and animals and the ecology of transmission by mosquitoes and their vertebrate hosts are rarely reported. Despite its association with meningitis in humans, TAHV is a neglected human pathogen with unknown public health importance in Central Europe, and a potential emerging disease threat elsewhere in Europe due to extreme summer flooding events.

Impact of green space connectivity on urban tick presence, density and Borrelia infected ticks in different habitats and seasons in three cities in southern England

Understanding the effects of local habitat and wider landscape connectivity factors on tick presence, nymph density and Borrelia species (spp.) prevalence in the tick population is important for identifying the public health risk from Lyme borreliosis. This multi-city study collected data in three southern England cities (Bath, Bristol, and Southampton) during spring, summer, and autumn in 2017. Focusing specifically on urban green space used for recreation which were clearly in urbanised areas, 72 locations were sampled. Additionally, geospatial datasets on urban green space coverage within 250 m and 1 km of sampling points, as well as distance to woodland were incorporated into statistical models. Distance to woodland was negatively associated with tick presence and nymph density, particularly during spring and summer. Furthermore, we observed an interaction effect between habitat and season for tick presence and nymph density, with woodland habitat having greater tick presence and nymph density during spring. Borrelia spp. infected Ixodes ricinus were found in woodland, woodland edge and under canopy habitats in Bath and Southampton. Overall Borrelia spp. prevalence in nymphs was 2.8%, similar to wider UK studies assessing prevalence in Ixodes ricinus in rural areas. Bird-related Borrelia genospecies dominated across sites, suggesting bird reservoir hosts may be important in urban green space settings for feeding and infecting ticks. Whilst overall density of infected nymphs across the three cities was low (0.03 per 100 m²), risk should be further investigated by incorporating data on tick bites acquired in urban settings, and subsequent Lyme borreliosis transmission.

Evidence for overwintering and autochthonous transmission of Usutu virus to wild birds following its redetection in the United Kingdom

Usutu virus (USUV) is an emerging zoonotic arbovirus in Europe, where it primarily impacts Eurasian blackbirds (Turdus merula). For mosquito-borne viruses to persist in temperate areas, transovarial transmission in vectors or overwintering in either hosts or diapausing vectors must occur to facilitate autochthonous transmission. We undertook surveillance of hosts and vectors in 2021 to elucidate whether USUV had overwintered in the United Kingdom (UK) following its initial detection there in 2020. From 175 dead bird submissions, we detected 1 case of USUV infection, in a blackbird, from which a full USUV genome was derived. Using a molecular clock analysis, we demonstrate that the 2021 detection shared a most recent common ancestor with the 2020 Greater London, UK, USUV sequence. In addition, we identified USUV-specific neutralizing antibodies in 10 out of 86 serum samples taken from captive birds at the index site, demonstrating in situ cryptic infection and potential sustained transmission. However, from 4966 mosquitoes, we detected no USUV RNA suggesting that prevalence in the vector community was absent or low during sampling. Combined, these results suggest that USUV overwintered in the UK, thus providing empirical evidence for the continued northward expansion of this vector-borne viral disease. Currently, our detection indicates geographically restricted virus persistence. Further detections over time will be required to demonstrate long-term establishment. It remains unclear whether the UK, and by extension other high-latitude regions, can support endemic USUV infection.

Spatial and temporal heterogeneity of the density of Borrelia burgdorferi-infected Ixodes ricinus ticks across a landscape: A 5-year study in southern England

The density of Borrelia burgdorferi-infected Ixodes ricinus nymphs (DIN) was investigated during 2013-2017 across a Lyme disease-endemic landscape in southern England. The density of nymphs (DON), nymph infection prevalence (NIP), and DIN varied across five different natural habitats, with the highest DIN in woodland edge and high biodiversity woodlands. DIN was significantly lower in scrub grassland compared to the woodland edge, with low DON and no evidence of infection in ticks in non-scrub grassland. Over the 5 years, DON, NIP and DIN were comparable within habitats, except in 2014, with NIP varying three-fold and DIN significantly lower compared to 2015-2017. Borrelia garinii was most common, with bird-associated Borrelia (B. garinii/valaisiana) accounting for ~70% of all typed sequences. Borrelia burgdorferi sensu stricto was more common than B. afzelii. Borrelia afzelii was more common in scrub grassland than woodland and absent in some years. The possible impact of scrub on grazed grassland, management of ecotonal woodland margins with public access, and the possible role of birds/gamebirds impacting NIP are discussed. Mean NIP was 7.6%, highlighting the potential risk posed by B. burgdorferi in this endemic area. There is a need for continued research to understand its complex ecology and identify strategies for minimizing risk to public health, through habitat/game management and public awareness.

Mosquito Magnet® traps as a potential means of monitoring blackflies of medical and veterinary importance

Mosquito Magnet® traps, deployed in widespread parts of England as part of nationwide mosquito surveillance projects, also caught blackflies. As many as 1242 blackflies were caught in a trapping session lasting 4 days. Principal among the species caught were Simulium equinum, Simulium lineatum and Simulium ornatum s.l. As S. ornatum s.l. is a vector that transmits Onchocerca linealis to cattle and S. equinum is responsible for dermatitis ('sweet itch') in cattle and horses, it is suggested that Mosquito Magnet® traps could be used to monitor and partially control these pests, as well as nuisance anthropophilic blackflies such as Simulium posticatum that can cause simuliidosis in southern England.

A nationwide study on Borrelia burgdorferi s.l. infection rates in questing Ixodes ricinus: a six-year snapshot study in protected recreational areas in England and Wales

Understanding the variation in Borrelia burgdorferi s.l. infection rates in Ixodes ricinus ticks is important for assessing the potential for Lyme borreliosis transmission. This study aimed to investigate infection rates of B. burgdorferi s.l. bacteria in I. ricinus across 24 field sites in England and Wales, focussing on protected recreational areas in National Parks (NPs) and Areas of Outstanding Natural Beauty (AONBs), to provide comparable data across multiple years to assess spatio-temporal changes in B. burgdorferi s.l. infection. Working with park rangers, questing ticks were collected each spring from 2014 to 2019. A subset of ticks, 4104 nymphs, were analysed using a pan-Borrelia qPCR assay, as well as a Borrelia miyamotoi-specific qPCR, and sequenced to determine Borrelia burgdorferi s.l. genospecies. Site-specific B. burgdorferi s.l. infection rates in I. ricinus nymphs varied from 0% to 24%, with overall infection rates ranging from 2.5% to 5.1% across the years. Genospecies composition of sequenced samples was 62.5% B. garinii, 20.3% B. valaisiana and 17.2% B. afzelii. Borrelia miyamotoi was detected in 0.2% of ticks. This study increases our knowledge on B. burgdorferi s.l.. infection in areas used by the public for outdoor activity across England and Wales, highlighting the spatial and temporal variability which can impact the changing risk to humans from infected tick bites.

Ixodes ricinus and Borrelia burgdorferi sensu lato in the Royal Parks of London, UK

Assessing the risk of tick-borne disease in areas with high visitor numbers is important from a public health perspective. Evidence suggests that tick presence, density, infection prevalence and the density of infected ticks can vary between habitats within urban green space, suggesting that the risk of Lyme borreliosis transmission can also vary. This study assessed nymph density, Borrelia prevalence and the density of infected nymphs across a range of habitat types in nine parks in London which receive millions of visitors each year. Ixodes ricinus were found in only two of the nine locations sampled, and here they were found in all types of habitat surveyed. Established I. ricinus populations were identified in the two largest parks, both of which had resident free-roaming deer populations. Highest densities of nymphs (15.68 per 100 m²) and infected nymphs (1.22 per 100 m²) were associated with woodland and under canopy habitats in Richmond Park, but ticks infected with Borrelia were found across all habitat types surveyed. Nymphs infected with Borrelia (7.9%) were only reported from Richmond Park, where Borrelia burgdorferi sensu stricto and Borrelia afzelii were identified as the dominant genospecies. Areas with short grass appeared to be less suitable for ticks and maintaining short grass in high footfall areas could be a good strategy for reducing the risk of Lyme borreliosis transmission to humans in such settings. In areas where this would create conflict with existing practices which aim to improve and/or meet historic landscape, biodiversity and public access goals, promoting public health awareness of tick-borne disease risks could also be utilised.

Update on the presence of Ixodes ricinus at the western limit of its range and the prevalence of Borrelia burgdorferi sensu lato

It is often suggested that due to climate and environmental policy changes, the risk from tick-borne disease is increasing, particularly at the geographical limits of the vector distribution. Our project aimed to determine whether this was true for the risk of Lyme borreliosis in Ireland which is the western-most limit of Ixodes ricinus, the European vector of Borrelia burgdorferi sensu lato. The availability of a historical data set of tick infection rates compiled in the 1990s represented a unique opportunity as it provided a baseline against which current data could be compared. Following construction of a spatial predictive model for the presence and absence of I. ricinus based on data from 491 GPS locations visited between 2016 and 2019, 1404 questing nymphs from 27 sites were screened for the presence of Borrelia spp. using a TaqMan PCR aimed at the 23S rRNA gene sequence. All positive ticks were further analysed by nested PCR amplification and sequence analysis of the 5 S-23 S intergenic spacer. The model indicated that areas with the highest probability of tick presence were mostly located along the western seaboard and the Shannon and Erne river catchments, coinciding with historical high incidence areas of bovine babesiosis, while the infection rate of questing nymphs with B. burgdorferi s.l. and the prevalence of the various genospecies have remained surprisingly stable over the last 3 decades. Clear communication of the potential disease risk arising from a tick bite is essential in order to allay undue concerns over tick-borne diseases among the general public.

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.

Ticks in the ecotone: the impact of agri-environment field margins on the presence and intensity of Ixodes ricinus ticks (Acari: Ixodidae) in farmland in southern England

The present study aimed to assess whether agri-environment field margins provide a habitat for the sheep/deer tick Ixodes ricinus. Field studies were conducted in arable farmland in southern England in both extant and newly constructed field margins. The presence and intensity (i.e. the mean number of nymphs per transect, excluding zeros) of questing nymphs and adult I. ricinus were compared between field margins with three adjacent habitats: woodland, hedgerow and arable land. The presence and intensity of ticks within a field margin was also compared between three ecozones: the ecotone, the margin and the crop. It was found that field margins do support I. ricinus, although the intensity of ticks was associated with field margins with adjacent woodland, with a higher tick intensity along the ecotonal ecozone, compared with the rest of the margin or the crop edge. The presence of a hedge also increased the likelihood of finding questing nymphs in a field margin compared with a margin adjacent to arable land. This effect, however, was less pronounced than in field margins with adjacent woodland. The provision of footpaths within the margin (at least 1-2 m from the ecotone), or on the edge of the crop where paths run next to woodland known to be an important tick habitat, could be promoted to minimize tick exposure. In addition, based on the results of the present study, raising awareness that walking alongside woodlands also constitutes a tick risk could be promoted.

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.

Invasive non-native species likely to threaten biodiversity and ecosystems in the Antarctic Peninsula region

The Antarctic is considered to be a pristine environment relative to other regions of the Earth, but it is increasingly vulnerable to invasions by marine, freshwater and terrestrial non-native species. The Antarctic Peninsula region (APR), which encompasses the Antarctic Peninsula, South Shetland Islands and South Orkney Islands, is by far the most invaded part of the Antarctica continent. The risk of introduction of invasive non-native species to the APR is likely to increase with predicted increases in the intensity, diversity and distribution of human activities. Parties that are signatories to the Antarctic Treaty have called for regional assessments of non-native species risk. In response, taxonomic and Antarctic experts undertook a horizon scanning exercise using expert opinion and consensus approaches to identify the species that are likely to present the highest risk to biodiversity and ecosystems within the APR over the next 10 years. One hundred and three species, currently absent in the APR, were identified as relevant for review, with 13 species identified as presenting a high risk of invading the APR. Marine invertebrates dominated the list of highest risk species, with flowering plants and terrestrial invertebrates also represented; however, vertebrate species were thought unlikely to establish in the APR within the 10 year timeframe. We recommend (a) the further development and application of biosecurity measures by all stakeholders active in the APR, including surveillance for species such as those identified during this horizon scanning exercise, and (b) use of this methodology across the other regions of Antarctica. Without the application of appropriate biosecurity measures, rates of introductions and invasions within the APR are likely to increase, resulting in negative consequences for the biodiversity of the whole continent, as introduced species establish and spread further due to climate change and increasing human activity.

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

Mosquito-borne diseases resulting from the expansion of two key vectors, Aedes aegypti and Aedes albopictus (Diptera: Culicidae), continue to challenge whole regions and continents around the globe. In recent years there have been human cases of disease associated with Chikungunya, dengue and Zika viruses. In Europe, the expansion of Ae. albopictus has resulted in local transmission of Chikungunya and dengue viruses. This paper considers the risk that Ae. aegypti and Ae. albopictus represent for the U.K. and details the results of mosquito surveillance activities. Surveillance was conducted at 34 points of entry, 12 sites serving vehicular traffic and two sites of used tyre importers. The most common native mosquito recorded was Culex pipiens s.l. (Diptera: Culicidae). The invasive mosquito Ae. albopictus was detected on three occasions in southern England (September 2016, July 2017 and July 2018) and subsequent control strategies were conducted. These latest surveillance results demonstrate ongoing incursions of Ae. albopictus into the U.K. via ground vehicular traffic, which can be expected to continue and increase as populations in nearby countries expand, particularly in France, which is the main source of ex-continental traffic.

Has the red sheep tick, Haemaphysalis punctata, recently expanded its range in England?

The red sheep tick, Haemaphysalis punctata (Ixodida: Ixodidae), has been reported as present in the U.K. for more than a century; however, very little has been written about its distribution. In recent years, numbers of detections of this tick species reported to the Public Health England (PHE) Tick Surveillance Scheme have increased. This rise in the number of records may be attributable to increased tick surveillance activities or to the increased distribution of this species of tick in parts of England. This paper reviews published reports of H. punctata and all data held by the Biological Records Centre and PHE, and summarizes a number of field studies conducted by PHE and the Animal and Plant Health Agency over the past 8 years. It would appear from the evidence presented here that H. punctata may be expanding its range across the eastern part of the South Downs National Park, where there have also been reports of this tick species biting humans. It is possible that the movement of sheep between grassland sites is facilitating this spread. Further studies that better elucidate the ecology of this tick and its possible role as a vector of human and veterinary diseases are now warranted.

Assessment of the Public Health Threats Posed by Vector-Borne Disease in the United Kingdom (UK)

In recent years, the known distribution of vector-borne diseases in Europe has changed, with much new information also available now on the status of vectors in the United Kingdom (UK). For example, in 2016, the UK reported their first detection of the non-native mosquito Aedes albopictus, which is a known vector for dengue and chikungunya virus. In 2010, Culex modestus, a principal mosquito vector for West Nile virus was detected in large numbers in the Thames estuary. For tick-borne diseases, data on the changing distribution of the Lyme borreliosis tick vector, Ixodes ricinus, has recently been published, at a time when there has been an increase in the numbers of reported human cases of Lyme disease. This paper brings together the latest surveillance data and pertinent research on vector-borne disease in the UK, and its relevance to public health. It highlights the need for continued vector surveillance systems to monitor our native mosquito and tick fauna, as well as the need to expand surveillance for invasive species. It illustrates the importance of maintaining surveillance capacity that is sufficient to ensure accurate and timely disease risk assessment to help mitigate the UK's changing emerging infectious disease risks, especially in a time of climatic and environmental change and increasing global connectivity.

Distribution of the tick Dermacentor reticulatus in the United Kingdom

The recent implication of Dermacentor reticulatus (Ixodida: Ixodidae) in the transmission of canine babesiosis in the U.K. has highlighted the lack of accurate published data on its distribution in this country. This paper aims to collate and appraise historical data for D. reticulatus, to supplement such data with more recent surveillance data and to report on field sampling conducted during 2009-2016. These updated data facilitate better understanding of the current distribution of this tick in the U.K., which will better inform disease risk assessments. There appear to be four known regions of the U.K. in which D. reticulatus currently occurs, including western Wales, North and South Devon, and Essex. The majority of foci are located in coastal sand dunes and maritime grasslands, including grazing marsh. However, more recently the tick has been detected in urban greenspace in Essex. The emergence of this tick as a vector of babesiosis in the U.K. and its recent apparent spread in Essex into urban greenspace highlight the need for continued surveillance and for further research into its status as a vector of human and veterinary pathogens.

Discovery of a single male Aedes aegypti (L.) in Merseyside, England

Background

The mosquito Aedes aegypti (L.) is found in tropical and sub-tropical regions where it is the major vector of dengue fever, yellow fever, chikungunya and more recently Zika virus. Given its importance as a vector of arboviruses and its propensity to be transported to new regions, the European Centre for Disease Prevention and Control (ECDC) has placed Ae. aegypti on a list of potentially invasive mosquito species. It was previously reported in the United Kingdom (UK) in 1865 and 1919 but did not establish on either occasion. It is now beginning to reappear in European countries and has been recorded in the Netherlands (not established) and Madeira (Portugal), as well as southern Russia, Georgia and Turkey.

Results

During summer 2014, a single male Ae. aegypti was captured during mosquito collections in north-western England using a sweep net. Morphological identification complimented by sequencing of the ITS2 rDNA, and cox1 mtDNA regions, confirmed the species. Following confirmation, a programme of targeted surveillance was implemented around the collection site by first identifying potential larval habitats in greenhouses, a cemetery, a farm and industrial units. Despite intensive surveillance around the location, no other Ae. aegypti specimens were collected using a combination of sweep netting, larval dipping, mosquito magnets, BG sentinel traps and ovitraps. All species collected were native to the UK.

Conclusion

The finding of the single male Ae. aegypti, while significant, presents no apparent disease risk to public health, and the follow-up survey suggests that there was no established population. However, this report does highlight the need for vigilance and robust surveillance, and the requirement for procedures to be in place to investigate such findings.

Tick infestation of small mammals in an English woodland

Tick infestations on small mammals were studied from April to November, 2010, in deciduous woodland in southern England in order to determine whether co-infestations with tick stages occurred on small mammals, a key requirement for endemic transmission of tick-borne encephalitis virus (TBEV). A total of 217 small mammals was trapped over 1,760 trap nights. Yellow-necked mice (Apodemus flavicollis) made up the majority (52.5%) of animals, followed by wood mice (A. sylvaticus) 35.5% and bank voles (Myodes glareolus) 12%. A total of 970 ticks was collected from 169 infested animals; 96% of ticks were Ixodes ricinus and 3% I. trianguliceps. Over 98% of ticks were larval stages. Mean infestation intensities of I. ricinus were significantly higher on A. flavicollis (6.53 ± 0.67) than on A. sylvaticus (4.96 ± 0.92) and M. glareolus (3.25 ± 0.53). Infestations with I. ricinus were significantly higher in August than in any other month. Co-infestations with I. ricinus nymphs and larvae were observed on six (3.6%) infested individuals, and fifteen small mammals (8.9%) supported I. ricinus - I. trianguliceps co-infestations. This work contributes further to our understanding of European small mammal hosts that maintain tick populations and their associated pathogens, and indicates that co-infestation of larvae and nymph ticks does occur in lowland UK. The possible implications for transmission of tick-borne encephalitis virus between UK ticks and small mammals are discussed.

Aedes nigrinus (Eckstein, 1918) (Diptera, Culicidae), a new country record for England, contrasted with Aedes sticticus (Meigen, 1838)

We report the discovery of Aedesnigrinus (Eckstein, 1918) in the New Forest of southern England, bringing to 36 the number of mosquito species recorded in Britain. Because it seems that this species has been misidentified previously in Britain as the morphologically similar Aedessticticus (Meigen, 1838), the two species are contrasted and distinguished based on distinctive differences exhibited in the adult and larval stages. The pupa of Ae.nigrinus is unknown, but the pupa of Ae.sticticus is distinguished from the pupae of other species of Aedes by modification of the most recent key to British mosquitoes. The history of the mosquito fauna recorded in the UK is summarized and bionomical information is provided for the two species.

First report of Rickettsia raoultii in field collected Dermacentor reticulatus ticks from Austria

In a set of pooled field collected Dermacentor reticulatus ticks, Rickettsia raoultii, the causative agent of Tick-borne lymphadenopathy/Dermacentor-borne necrosis erythema and lymphadenopathy, was found for the first time in Austria. The coordinates of the positive locations for tick and pathogen abundance are given and shown in a map.

Current status of invasive mosquito surveillance in the UK

BACKGROUND

Non-native invasive mosquitoes have for many years made incursions into Europe, and are now established in many European countries. The continued European importation of potential vectors and their expansion within Europe increases their potential for importation and establishment in the UK. Coupled with increasing numbers of returning dengue and chikungunya infected travellers, the potential exists for transmission of vector borne disease in new regions.

METHODS

To ensure a cost-effective risk assessment and preparedness strategy the UK employs a multi-faceted approach to surveillance for non-native Aedes mosquitoes, including passive and active surveillance strategies at a local, regional, and national level. Passive surveillance, including a national mosquito recording scheme and local authority nuisance biting reporting, are combined with targeted active surveillance at seaports, airports, used tyre importers, and motorway service stations.

RESULTS

There is no evidence to date that any invasive Aedes species (e.g., Aedes albopictus, Aedes japonicus, Aedes aegypti) occur in the UK despite sharing many of the same routes that have been found to have facilitated their entry into other countries.

CONCLUSIONS

This paper sets in context the UK approaches with other European countries and those recommended by the ECDC. It also highlights future UK strategies to enhance surveillance for non-native mosquitoes to help ensure that incursions can be managed, and these mosquitoes do not establish and public health is protected. Focus will be given to increasing the number of submissions of mosquitoes to passive surveillance schemes and maintaining active surveillance efforts at key routes of potential importation.

Seasonal dynamics and habitat specificity of mosquitoes in an English wetland: implications for UK wetland management and restoration

We engaged in field studies of native mosquitoes in a Cambridgeshire Fen, investigating a) the habitat specificity and seasonal dynamics of our native fauna in an intensively managed wetland, b) the impact of water-level and ditch management, and c) their colonization of an arable reversion to flooded grassland wetland expansion project. Studies from April to October, 2010 collected 14,000 adult mosquitoes (15 species) over 292 trap-nights and ∼4,000 pre-imaginal mosquitoes (11 species). Open floodwater species (Aedes caspius and Aedes cinereus, 43.3%) and wet woodland species (Aedes cantans/annulipes and Aedes rusticus, 32.4%) dominated, highlighting the major impact of seasonal water-level management on mosquito populations in an intensively managed wetland. In permanent habitats, managing marginal ditch vegetation and ditch drying significantly affect densities of pre-imaginal anophelines and culicines, respectively. This study presents the first UK field evidence of the implications of wetland expansion through arable reversion on mosquito colonization. Understanding the heterogeneity of mosquito diversity, phenology, and abundance in intensively managed UK wetlands will be crucial to mitigating nuisance and vector species through habitat management and biocidal control.

Approaches to passive mosquito surveillance in the EU

The recent emergence in Europe of invasive mosquitoes and mosquito-borne disease associated with both invasive and native mosquito species has prompted intensified mosquito vector research in most European countries. Central to the efforts are mosquito monitoring and surveillance activities in order to assess the current species occurrence, distribution and, when possible, abundance, in order to permit the early detection of invasive species and the spread of competent vectors. As active mosquito collection, e.g. by trapping adults, dipping preimaginal developmental stages or ovitrapping, is usually cost-, time- and labour-intensive and can cover only small parts of a country, passive data collection approaches are gradually being integrated into monitoring programmes. Thus, scientists in several EU member states have recently initiated programmes for mosquito data collection and analysis that make use of sources other than targeted mosquito collection. While some of them extract mosquito distribution data from zoological databases established in other contexts, community-based approaches built upon the recognition, reporting, collection and submission of mosquito specimens by citizens are becoming more and more popular and increasingly support scientific research. Based on such reports and submissions, new populations, extended or new distribution areas and temporal activity patterns of invasive and native mosquito species were found. In all cases, extensive media work and communication with the participating individuals or groups was fundamental for success. The presented projects demonstrate that passive approaches are powerful tools to survey the mosquito fauna in order to supplement active mosquito surveillance strategies and render them more focused. Their ability to continuously produce biological data permits the early recognition of changes in the mosquito fauna that may have an impact on biting nuisance and the risk of pathogen transmission associated with mosquitoes. International coordination to explore synergies and increase efficiency of passive surveillance programmes across borders needs to be established.

Colonization of a newly constructed urban wetland by mosquitoes in England: implications for nuisance and vector species

Urban wetlands are being created in the UK as part of sustainable urban drainage strategies, to create wetland habitats lost during development, to provide a habitat for protected species, and to increase the public's access to 'blue-space' for the improvement of health and well-being. Sewage treatment reedbeds are also being incorporated into newly constructed wetlands to offer an alternative approach to dealing with sewage. This field study aims to provide the first UK evidence of how such newly constructed aquatic habitats are colonized by mosquitoes. A number of new aquatic habitats were surveyed for immature mosquitoes every fortnight over the first two years following wetland construction. The majority of mosquitoes collected were Culex sp. and were significantly associated with the sewage treatment reedbed system, particularly following storm events and sewage inflow. Other more natural aquatic habitats that were subject to cycles of drying and re-wetting contributed the majority of the remaining mosquitoes colonizing. Colonization of permanent habitats was slow, particularly where fluctuations in water levels inhibited emergent vegetation growth. It is recommended that during the planning process for newly constructed wetlands consideration is given on a case-by-case basis to the impact of mosquitoes, either as a cause of nuisance or as potential vectors. Although ornithophagic Culex dominated in this wetland, their potential role as enzootic West Nile virus vectors should not be overlooked.

Colonization of UK coastal realignment sites by mosquitoes: implications for design, management, and public health

Coastal realignment is now widely instituted in the UK as part of local flood risk management plans to compensate for the loss of European protected habitat and to mitigate the effects of sea-level rise and coastal squeeze. Coastal aquatic habitats have long been known to provide suitable habitats for brackish-water mosquitoes and historically, coastal marshes were considered to support anopheline mosquito populations that were responsible for local malaria transmission. This study surveyed the eight largest managed realignment (MRA) sites in England (Essex and the Humber) for mosquito habitats. The apparent absence of anopheline mosquitoes exploiting aquatic habitats at all of these sites suggests that the risk of malaria associated with MRA sites is currently negligible. However, three of the eight sites supported populations of two nuisance and potential arboviral vector species, Aedes detritus and Aedes caspius. The aquatic habitats that supported mosquitoes resulted from a) specific design aspects of the new sea wall (ballast to mitigate wave action and constructed saline borrow ditches) that could be designed out or managed or b) isolated pools created through silt accretion or expansion of flooded zones to neighbouring pasture. The public health risks and recommendations for management are discussed in this report. This report highlights the need for pro-active public health impact assessments prior to MRA development in consultation with the Health Protection Agency, as well as the need for a case-by-case approach to design and management to mitigate mosquito or mosquito-borne disease issues now and in the future.

Detection of mosquito-only flaviviruses in Europe

The genus Flavivirus, family Flaviviridae, includes a number of important arthropod-transmitted human pathogens such as dengue viruses, West Nile virus, Japanese encephalitis virus and yellow fever virus. In addition, the genus includes flaviviruses without a known vertebrate reservoir, which have been detected only in insects, particularly in mosquitoes, such as cell fusing agent virus, Kamiti River virus, Culex flavivirus, Aedes flavivirus, Quang Binh virus, Nakiwogo virus and Calbertado virus. Reports of the detection of these viruses with no recognized pathogenic role in humans are increasing in mosquitoes collected around the world, particularly in those sampled in entomological surveys targeting pathogenic flaviviruses. The presence of six potential flaviviruses, detected from independent European arbovirus surveys undertaken in the Czech Republic, Italy,Portugal, Spain and the UK between 2007 and 2010, is reported in this work. Whilst the Aedes flaviviruses, detected in Italy from Aedes albopictus mosquitoes, had already been isolated in Japan, the remaining five viruses have not been reported previously: one was detected in Italy, Portugal and Spain from Aedes mosquitoes (particularly from Aedes caspius), one in Portugal and Spain from Culex theileri mosquitoes, one in the Czech Republic and Italy from Aedes vexans, one in the Czech Republic from Aedes vexans and the last in the UK from Aedes cinereus. Phylogenetic analysis confirmed the close relationship of these putative viruses to other insect-only flaviviruses.

West Nile virus vector Culex modestus established in southern England

Background

The risk posed to the United Kingdom by West Nile virus (WNV) has previously been considered low, due to the absence or scarcity of the main Culex sp. bridge vectors. The mosquito Culex modestus is widespread in southern Europe, where it acts as the principle bridge vector of WNV. This species was not previously thought to be present in the United Kingdom.

Findings

Mosquito larval surveys carried out in 2010 identified substantial populations of Cx. modestus at two sites in marshland in southeast England. Host-seeking-adult traps placed at a third site indicate that the relative seasonal abundance of Cx. modestus peaks in early August. DNA barcoding of these specimens from the United Kingdom and material from southern France confirmed the morphological identification.

Conclusions

Cx. modestus appears to be established in the North Kent Marshes, possibly as the result of a recent introduction. The addition of this species to the United Kingdom's mosquito fauna may increase the risk posed to the United Kingdom by WNV.

Importation of Hyalomma marginatum, vector of Crimean-Congo haemorrhagic fever virus, into the United Kingdom by migratory birds

Hyalomma marginatum ticks are an important vector of Crimean-Congo haemorrhagic fever virus which can result in a severe and potentially fatal disease in humans. Given the continued emergence of clinical cases in Eurasia and focalised upsurges of H. marginatum populations in Europe, it seemed prudent to assess the potential of this vector species to be introduced into the United Kingdom. Immature forms of H. marginatum are frequent ectoparasites of passerine birds many of which migrate from Africa to the UK each spring. Incoming birds were inspected for ticks during the spring migration in 2010 and 2011. A total of 68 ticks was collected from 971 birds (29 bird species), 21% (14) of the ticks were identified as H. marginatum. Oenanthe oenanthe (Northern wheatear) and Sylvia communis (Whitethroat) were found to be infested by this tick in both years and with multiple ticks. Single specimens were also removed from Acrocephalus schoenobaenus (Sedge warbler) and Phoenicurus phoenicurus (Common redstart) in 2010. This study provides the first contemporary evidence for substantial importation of this tick species into the UK.