Lara E. Harrup

Bluetongue in Europe and the Mediterranean Basin: history of occurrence prior to 2006.

Bluetongue virus (BTV) exists around the world in a broad band covering much of the Americas, Africa, southern Asia and northern Australia. Historically, it also occasionally occurred in the southern fringes of Europe. It is considered to be one of the most important diseases of domestic livestock. Recently BTV has extended its range northwards into areas of Europe never before affected and has persisted in many of these locations causing the greatest epizootic of bluetongue (BT), the disease caused by BTV, on record. Indeed, the most recent outbreaks of BT in Europe are further north than this virus has ever previously occurred anywhere in the world. The reasons for this dramatic change in BT epidemiology are complex but are linked to recent extensions in the distribution of its major vector, Culicoides imicola, to the involvement of novel Culicoides vector(s) and to on-going climate-change. This paper investigates these recent outbreaks in the European theatre, up to the beginning of 2006, highlights prospects for the future and sets the scene for the following papers in this special issue.

Bluetongue in Europe and the Mediterranean Basin

This chapter explores the areas of occurrence of bluetongue virus (BTV) in the European region. It highlights prospects for the future and discusses recent findings relating to the ability of BTV-8 to overwinter in northern Europe. Bluetongue exists around the world in a broad band covering much of the America, Africa, southern Asia, northern Australia and, occasionally, the southern fringe of Europe. It is considered to be one of the most important diseases of domestic livestock. Recently the virus causing this disease has extended its range northwards into areas of Europe never before affected and has persisted in many of these locations causing the greatest epizootic of the disease on record. Indeed, the most recent outbreaks of BT in Europe are further north than this virus has ever previously occurred anywhere in the world. The reasons for this dramatic change in BT epidemiology are complex but are linked to recent extensions in the distribution of its major vector, C. imicola, to the involvement of novel Culicoides vector(s) and to ongoing climate change.

Culicoides Latreille (Diptera: Ceratopogonidae) taxonomy: current challenges and future directions

Highlights • We review tools for Culicoides species identification using both morphological and genetic characterisation.• We review progress in integrative taxonomy in Culicoides.• We present the current global status of Culicoides taxonomic knowledge.• Present conclusions on the current status in Culicoides taxonomy and systematics and prospects for the future.

Investigation of Diel Activity of Culicoides Biting Midges (Diptera: Ceratopogonidae) in the United Kingdom by Using a Vehicle-Mounted Trap

ABSTRACT Truck trap collections of Culicoides biting midges (Diptera: Ceratopogonidae) were made during 2 yr of sampling from 2008 to 2009 at a farm site in southern England. Samples were collected from 810 sample runs carried out over 52 d and contained 7,095 Culicoides of which more than half (50.3%) were identified as Culicoides obsoletus Meigen by using a multiplex polymerase chain reaction assay. Other commonly encountered species included Culicoides scoticus Downes & Kettle (14.7% of total Culicoides caught), Culicoides dewulfi Goetghebuer (3.7%), and Culicoides chiopterus Meigen (4.2%). The activity rates of these species were examined with regard to both meteorological factors (light intensity, humidity, temperature, and wind speed and direction) and other potentially contributing variables (lunar phase and brightness, sunset time, and year) by using generalized linear models. All the species examined were collected in greater abundance at sunset, although the relationship between underlying light intensity and numbers was less pronounced in C. dewulfi and C. chiopterus. Collections of Culicoides were reduced at temperatures above 21°C and were inversely related to wind speed. Variation between species was recorded, however, in response to wind direction: C. dewulfi and C. chiopterus were associated with prevailing winds passing through fields containing livestock, whereas C. obsoletus and C. scoticus demonstrated no such relationship. A male:female ratio of 1:3.56 was observed in catches, and male populations were protandrous. These results are discussed with reference both to the ecology of these species and methods currently used to predict adult Culicoides movement and abundance in Europe.

Testing of UK Populations of Culex pipiens L. for Schmallenberg Virus Vector Competence and Their Colonization

Background Schmallenberg virus (SBV), an arboviral pathogen of ruminants, emerged in northern Europe during 2011 and has subsequently spread across a vast geographic area. While Culicoides biting midges (Diptera: Ceratopogonidae) have been identified as a biological transmission agent of SBV, the role of mosquitoes (Diptera: Culicidae) as potential vectors has not been defined beyond small-scale field collections in affected areas. Culex pipiens L. are one of the most widespread mosquitoes in northern Europe; they are present on farms across the region and have previously been implicated as vectors of several other arboviruses. We assessed the ability of three colony lines of Cx. pipiens, originating from geographically diverse field populations, to become fully infected by SBV using semi-quantitative real-time RT-PCR (sqPCR). Findings Two colony lines of Cx. pipiens were created in the UK (‘Brookwood’ and ‘Caldbeck’) from field collections of larvae and pupae and characterised using genetic markers. A third strain of Cx. pipiens from CVI Wageningen, The Netherlands, was also screened during experiments. Intrathoracic inoculation of the Brookwood line resulted in infections after 14 days that were characterised by high levels of RNA throughout individuals, but which demonstrated indirect evidence of salivary gland barriers. Feeding of 322 individuals across the three colony lines on a membrane based infection system resulted in no evidence of full dissemination of SBV, although infections did occur in a small proportion of Cx. pipiens from each line. Conclusions/Significance This study established two novel lines of Cx. pipiens mosquitoes of UK origin in the laboratory and subsequently tested their competence for SBV. Schmallenberg virus replication and dissemination was restricted, demonstrating that Cx. pipiens is unlikely to be an epidemiologically important vector of the virus in northern Europe.

Advances in control techniques for Culicoides and future prospects.

In most instances, vaccination is accepted to be the most effective method of preventing Culicoides-borne arbovirus transmission, as it has proven to be successful in large-scale campaigns. Under certain scenarios, however, vaccines require time to be developed and deployed or are not used due to financial, logistical or trade constraints. In the absence of vaccines, animal movement restrictions and techniques to reduce either the number of Culicoides biting livestock or their subsequent survival are the only responses available to prevent or reduce arbovirus transmission and spread. This review evaluates the progress made during the past 10 years in the development of Culicoides control techniques for this purpose and assesses their potential impact in reducing arbovirus transmission. In addition, the future prospects and challenges facing Culicoides control are examined and suggestions are made as to research directions and opportunities.

How often do mosquitoes bite humans in southern England?: a standardised summer trial at four sites reveals spatial, temporal and site-related variation in biting rates

BackgroundThis field-based study examined the abundance and species complement of mosquitoes (Diptera: Culicidae) attracted to humans at four sites in the United Kingdom (UK). The study used a systematic approach to directly measure feeding by mosquitoes on humans at multiple sites and using multiple volunteers. Quantifying how frequently humans are bitten in the field by mosquitoes is a fundamental parameter in assessing arthropod-borne virus transmission.MethodsHuman landing catches were conducted using a standardised protocol by multiple volunteers at four rural sites between July and August 2013. Collections commenced two hours prior to sunset and lasted for a total of four hours. To reduce bias occurring due to collection point or to the individual attractiveness of the volunteer to mosquitoes, each collection was divided into eight collection periods, with volunteers rotated by randomised Latin square design between four sampling points per site. While the aim was to collect mosquitoes prior to feeding, the source of blood meals from any engorged specimens was also identified by DNA barcoding.ResultsThree of the four sites yielded human-biting mosquito populations for a total of 915 mosquitoes of fifteen species/species groups. Mosquito species composition and biting rates differed significantly between sites, with individual volunteers collecting between 0 and 89 mosquitoes (over 200 per hour) of up to six species per collection period. Coquillettidia richiardii (Ficalbi, 1889) was responsible for the highest recorded biting rates at any one site, reaching 161 bites per hour, whilst maximum biting rates of 55 bites per hour were recorded for Culex modestus (Ficalbi, 1889). Human-biting by Culex pipiens (L., 1758) form pipiens was also observed at two sites, but at much lower rates when compared to other species.ConclusionsSeveral mosquito species are responsible for human nuisance biting pressure in southern England, although human exposure to biting may be largely limited to evening outdoor activities. This study indicates Cx. modestus can be a major human-biting species in the UK whilst Cx. pipiens f. pipiens may show greater opportunistic human-biting than indicated by earlier studies.

Blood-feeding, susceptibility to infection with Schmallenberg virus and phylogenetics of Culicoides (Diptera: Ceratopogonidae) from the United Kingdom

BackgroundCulicoides biting midges (Diptera: Ceratopogonidae) are responsible for the biological transmission of internationally important arboviruses of livestock. In 2011, a novel Orthobunyavirus was discovered in northern Europe causing congenital malformations and abortions in ruminants. From field studies, Culicoides were implicated in the transmission of this virus which was subsequently named Schmallenberg virus (SBV), but to date no assessment of susceptibility to infection of field populations under standardised laboratory conditions has been carried out. We assessed the influence of membrane type (chick skin, collagen, Parafilm M®) when offered in conjunction with an artificial blood-feeding system (Hemotek, UK) on field-collected Culicoides blood-feeding rates. Susceptibility to infection with SBV following blood-feeding on an SBV-blood suspension provided via either (i) the Hemotek system or via (ii) a saturated cotton wool pledglet was then compared. Schmallenberg virus susceptibility was defined by RT-qPCR of RNA extractions of head homogenates and related to Culicoides species and haplotype identifications based on the DNA barcode region of the mitochondrial cytochrome c oxidase 1 (cox1) gene.ResultsCulicoides blood-feeding rates were low across all membrane types tested (7.5% chick skin, 0.0% for collagen, 4.4% Parafilm M®, with 6029 female Culicoides being offered a blood meal in total). Susceptibility to infection with SBV through membrane blood-feeding (8 of 109 individuals tested) and pledglet blood-feeding (1 of 94 individuals tested) was demonstrated for the Obsoletus complex, with both C. obsoletus (Meigen) and C. scoticus Downes & Kettle susceptible to infection with SBV through oral feeding. Potential evidence of cryptic species within UK populations was found for the Obsoletus complex in phylogenetic analyses of cox1 DNA barcodes of 74 individuals assessed from a single field-site.ConclusionsMethods described in this study provide the means to blood-feed Palaearctic Culicoides for vector competence studies and colonisation attempts. Susceptibility to SBV infection was 7.3% for membrane-fed members of the subgenus Avaritia and 1.1% for pledglet-fed. Both C. obsoletus and C. scoticus were confirmed as being susceptible to infection with SBV, with potential evidence of cryptic species within UK Obsoletus complex specimens, however the implications of cryptic diversity in the Obsoletus complex on arbovirus transmission remains unknown.

Quantification of within- and between-farm dispersal of Culicoides biting midges using an immunomarking technique

Summary Culicoides biting midges (Diptera, Ceratopogonidae) are vectors of arboviruses that cause significant economic and welfare impact. Local‐scale spread of Culicoides‐borne arboviruses is largely determined by the between‐farm movement of infected Culicoides. Study of the dispersal behaviour of Culicoides by capture–mark–recapture (CMR) is problematic due to the likelihood of mortality and changes in behaviour upon capture caused by the small size and fragility of these insects, evidenced by low recapture rates. To counter the problem of using CMR with Culicoides, this study utilised an ovalbumin immunomarking technique to quantify the within‐ and between‐farm dispersal of Culicoides in southern England. Both within‐ and between‐farm dispersal of Culicoides was observed. Of the 9058 Culicoides collected over 22 nights of trapping, 600 ovalbumin‐positive Culicoides, of 12 species including those implicated as arbovirus vectors, were collected with a maximum dispersal distance of 3125 m. This study provides the first species‐level data on the between‐farm dispersal of potential bluetongue, Schmallenberg and African horse sickness virus vectors in northern Europe. High‐resolution meteorological data determined upwind and downwind flight by Culicoides had occurred. Cumulative collection and meteorological data suggest 15·6% of flights over 1 km were upwind of the treatment area and 84·4% downwind. Synthesis and applications. The use of immunomarking eliminates the potential adverse effects on survival and behaviour of insect collection prior to marking, substantially improving the resolution and accuracy of estimates of the dispersal potential of small and delicate vector species such as Culicoides. Using this technique, quantification of the range of Culicoides dispersal with regard to meteorological conditions including wind direction will enable improved, data‐driven modelling of the spread of Culicoides‐borne arboviruses and will inform policy response to incursions and outbreaks.

Spatial and temporal distribution of Culicoides species in mainland Portugal (2005-2010). Results of the Portuguese Entomological Surveillance Programme.

Bluetongue virus (BTV) is transmitted by Culicoides biting midges and causes an infectious, non-contagious disease of ruminants. It has been rapidly emerging in southern Europe since 1998. In mainland Portugal, strains of BTV belonging to three serotypes have been detected: BTV-10 (1956-1960), BTV-4 (2004-2006 and 2013) and BTV-1 (2007-2012). This paper describes the design, implementation and results of the Entomological Surveillance Programme covering mainland Portugal, between 2005 and 2010, including 5,650 caches. Culicoides imicola Kieffer was mostly found in central and southern regions of Portugal, although it was sporadically detected in northern latitudes. Its peak activity occurred in the autumn and it was active during the winter months in limited areas of the country. Obsoletus group was present at the highest densities in the north although they were found throughout the country in substantial numbers. Culicoides activity occurred all year round but peaked in the spring. A generalized linear mixed model was developed for the analysis of the environmental factors associated with activity of the species of Culicoides suspected vectors of BTV in the country. For C. imicola Kieffer, the most important variables were month, diurnal temperature range (DTR), the number of frost days (FRS) and median monthly temperature (TMP). For the Obsoletus group, the most important factors were month, diurnal temperature range (DTR), and linear and quadratic terms for median monthly temperature (TMP). The results reported can improve our understanding of climatic factors in Culicoides activity influencing their distribution and seasonal pattern.