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

Modelling African horse sickness emergence and transmission in the South African control area using a deterministic metapopulation approach

African horse sickness is an equine orbivirus transmitted by Culicoides Latreille biting midges. In the last 80 years, it has caused several devastating outbreaks in the equine population in Europe, the Far and Middle East, North Africa, South-East Asia, and sub-Saharan Africa. The disease is endemic in South Africa; however, a unique control area has been set up in the Western Cape where increased surveillance and control measures have been put in place. A deterministic metapopulation model was developed to explore if an outbreak might occur, and how it might develop, if a latently infected horse was to be imported into the control area, by varying the geographical location and months of import. To do this, a previously published ordinary differential equation model was developed with a metapopulation approach and included a vaccinated horse population. Outbreak length, time to peak infection, number of infected horses at the peak, number of horses overall affected (recovered or dead), re-emergence, and Rv (the basic reproduction number in the presence of vaccination) were recorded and displayed using GIS mapping. The model predictions were compared to previous outbreak data to ensure validity. The warmer months (November to March) had longer outbreaks than the colder months (May to September), took more time to reach the peak, and had a greater total outbreak size with more horses infected at the peak. Rv appeared to be a poor predictor of outbreak dynamics for this simulation. A sensitivity analysis indicated that control measures such as vaccination and vector control are potentially effective to manage the spread of an outbreak, and shortening the vaccination window to July to September may reduce the risk of vaccine-associated outbreaks.

Host Associations of Culicoides Biting Midges in Northeastern Kansas, USA

Culicoides biting midges (Diptera: Ceratopogonidae) are hematophagous flies that transmit several viruses of veterinary concern to livestock. Understanding blood feeding behaviors is integral towards identification of putative vector species and preventing the transmission of these pathogens. PCR-based blood meal analysis was conducted on 440 blood-engorged Culicoides midges collected in northeastern Kansas, with 316 (71.8%) returning non-human vertebrate identifications at the ≥95% identity match level. Broadly, Culicoides sonorensis, Culicoides stellifer, and Culicoides variipennis were found to feed heavily on mammalian hosts, while Culicoides crepuscularis and Culicoides haematopotus fed on avian hosts. The blood meals in all specimens were graded prior to DNA extraction to determine whether blood meal size or digestion status significantly impacted the likelihood of a quality host match. Size had a significant impact on the likelihood of a quality match at grades 3-5, whereas digestion only significantly impacted outcomes at the most extreme grade. These vector-host dynamics have not previously been studied in Culicoides collected in Kansas, which represents a unique tallgrass prairie biome within the United States that is heavily interspersed with livestock operations. Based on these data, the highly abundant species C. crepuscularis and C. haematopotus are unlikely to be major vectors of mammalian viruses.

Equine allergic skin diseases: Clinical consensus guidelines of the World Association for Veterinary Dermatology

BACKGROUND

Allergic skin diseases are common in horses worldwide. The most common causes are insect bites and environmental allergens.

OBJECTIVES

To review the current literature and provide consensus on pathogenesis, diagnosis, treatment and prevention.

MATERIALS AND METHODS

The authors reviewed the literature up to November 2022. Results were presented at North America Veterinary Dermatology Forum (2021) and European Veterinary Dermatology Congress (2021). The report was available to member organisations of the World Association for Veterinary Dermatology for feedback.

CONCLUSIONS AND CLINICAL RELEVANCE

Insect bite hypersensitivity (IBH) is the best characterised allergic skin disease. An immunoglobulin (Ig)E response against Culicoides salivary antigens is widely documented. Genetics and environmental factors play important roles. Tests with high sensitivity and specificity are lacking, and diagnosis of IBH is based on clinical signs, seasonality and response to insect control. Eosinophils, interleukin (IL)-5 and IL-31 are explored as therapeutic targets. Presently, the most effective treatment is insect avoidance. Existing evidence does not support allergen-specific immunotherapy (ASIT) using commercially available extracts of Culicoides. Hypersensitivity to environmental allergens (atopic dermatitis) is the next most common allergy. A role for IgE is supported by serological investigation, skin test studies and positive response to ASIT. Prospective, controlled, randomised studies are limited, and treatment relies largely on glucocorticoids, antihistamines and ASIT based on retrospective studies. Foods are known triggers for urticaria, yet their role in pruritic dermatitis is unknown. Recurrent urticaria is common in horses, yet our understanding is limited and focussed on IgE and T-helper 2 cell response. Prospective, controlled studies on treatments for urticaria are lacking. Glucocorticoids and antihistamines are primary reported treatments.

Using Zoos as Sentinels for Re-Emerging Arboviruses: Vector Surveillance during an Outbreak of Epizootic Hemorrhagic Disease at the Minnesota Zoo

Vector-borne disease prevalence is increasing at a time when surveillance capacity in the United States is decreasing. One way to address this surveillance deficiency is to utilize established infrastructure, such as zoological parks, to investigate animal disease outbreaks and improve our epidemiological understanding of vector-borne pathogens. During fall 2020, an outbreak of epizootic hemorrhagic disease (EHD) at the Minnesota Zoo resulted in morbidity and seroconversion of several collection animals. In response to this outbreak, insect surveillance was conducted, and the collected insects were tested for the presence of epizootic hemorrhagic disease virus (EHDV) by RT-qPCR to better understand the local transmitting vector populations responsible for the outbreak. Six pools of Culicoides biting midges were positive for EHDV, including three pools of Culicoides sonorensis, two pools of Culicoides variipennis, and a pool of degraded C. variipennis complex midges. All three endemic serotypes of EHDV (1, 2, and 6) were detected in both animals and midge pools from the premises. Despite this outbreak, no EHDV cases had been reported in wild animals near the zoo. This highlights the importance and utility of using animal holding facilities, such as zoos, as sentinels to better understand the spatio-temporal dynamics of pathogen transmission.

Seroprevalence and Epidemiological Risk Factors for Kasba Virus Among Sheep and Goats in South Korea: A Nationwide Retrospective Study

Introduction

Kasba virus belongs to the Palyam serogroup of the Orbivirus genus and Reoviridae family. Kasba virus is the causative agent of many reproductive disorders in infected animals, which result in considerable economic losses, mainly in the cattle industry. The epidemiology of Kasba virus infection is poorly defined and remains unclear in South Korea.

Material and Methods

This study investigated the prevalence of antibodies against Kasba virus in sheep and goats in South Korea. Individual, management, and regional risk factors associated with seropositivity were also evaluated. In addition, a retrospective serosurvey was conducted.

Results

Serum samples from 28 out of 441 sheep or goat flocks (6.3%, 95% confidence interval (CI): 4.4-9.0%) and 115 out of 1003 animals (11.5%, 95% CI 9.6-13.6%) were positive for antibodies against Kasba virus. According to our results, a history of reproductive problems increased the probability of Kasba virus positivity. Preventive measures such as routine insecticide application decreased this probability. We observed significant differences in the prevalence of seropositivity between southern provinces and northern provinces and between western provinces and eastern provinces at the individual level.

Conclusion

The virus was widely distributed among sheep and goats in South Korea, with seropositivity ranging from 6.8% in 2004 to 13.7% in 2008. The current study represents the first assessment of factors associated with Kasba virus seroprevalence in sheep and goats in South Korea.

Factors associated with seropositivity to Aino virus among sheep and goats in South Korea

Aino virus infection is responsible for epizootic and/or sporadic outbreaks of abortions, stillbirths and premature delivery among pregnant ruminants. The epizootiology of Aino virus infection is poorly defined in South Korea, therefore our aim was to assess its seroprevalence among sheep and goats. We also wanted to evaluate management and regional risk factors that might influence the frequency of infection. Between 2012 and 2013, 26 of 331 flocks (7.9%) and 139 of 915 heads (15.2%) were found serologically positive. In 2018, when samples were again collected in the same regions, 35 of 308 flocks (11.4%) and 89 of 735 heads (12.1%) showed serum-neutralising antibodies against Aino virus. Our results revealed that the age class and history of reproductive problems in the flocks are connected to an increased risk of being positive. The management risk factor attributes showed that preventive measures, such as the routine application of insecticide in farms, decreased the odds for seropositivity to Aino virus (OR = 0.453, P = 0.001). We observed a significant difference in the individual likelihood of being positive in the southern and western provinces with respect to that in the northern and eastern provinces, respectively (OR = 2.199, P < 0.001 and OR = 2.177, P < 0.001). The results of this study may serve as a basis for future epizootic studies on Aino virus infection in South Korea.

A Qualitative Risk Assessment for Bluetongue Disease and African Horse Sickness: The Risk of Entry and Exposure at a UK Zoo

Bluetongue virus (BTV) and African horse sickness virus (AHSV) cause economically important diseases that are currently exotic to the United Kingdom (UK), but have significant potential for introduction and onward transmission. Given the susceptibility of animals kept in zoo collections to vector-borne diseases, a qualitative risk assessment for the introduction of BTV and AHSV to ZSL London Zoo was performed. Risk pathways for each virus were identified and assessed using published literature, animal import data and outputs from epidemiological models. Direct imports of infected animals, as well as wind-borne infected Culicoides, were considered as routes of incursion. The proximity of ongoing disease events in mainland Europe and proven capability of transmission to the UK places ZSL London Zoo at higher risk of BTV release and exposure (estimated as low to medium) than AHSV (estimated as very low to low). The recent long-range expansion of AHSV into Thailand from southern Africa highlights the need for vector competence studies of Palearctic Culicoides for AHSV to assess the risk of transmission in this region.

Analysis of bluetongue disease epizootics in sheep of Andhra Pradesh, India using spatial and temporal autocorrelation

Bluetongue (BT) disease poses a constant risk to the livestock population around the world. A better understanding of the risk factors will enable a more accurate prediction of the place and time of high-risk events. Mapping the disease epizootics over a period in a particular geographic area will identify the spatial distribution of disease occurrence. A Geographical Information System (GIS) based methodology to analyze the relationship between bluetongue epizootics and spatial-temporal patterns was used for the years 2000 to 2015 in sheep of Andhra Pradesh, India. Autocorrelation (ACF), partial autocorrelation (PACF), and cross-correlation (CCF) analyses were carried out to find the self-dependency between BT epizootics and their dependencies on environmental factors and livestock population. The association with climatic or remote sensing variables at different months lag, including wind speed, temperature, rainfall, relative humidity, normalized difference vegetation index (NDVI), normalized difference water index (NDWI), land surface temperature (LST), was also examined. The ACF & PACF of BT epizootics with its lag showed a significant positive autocorrelation with a month's lag (r = 0.41). Cross-correlations between the environmental variables and BT epizootics indicated the significant positive correlations at 0, 1, and 2 month's lag of rainfall, relative humidity, normalized difference water index (NDWI), and normalized difference vegetation index (NDVI). Spatial autocorrelation analysis estimated the univariate global Moran's I value of 0.21. Meanwhile, the local Moran's I value for the year 2000 (r = 0.32) showed a high degree of spatial autocorrelation. The spatial autocorrelation analysis revealed that the BT epizootics in sheep are having considerable spatial association among the outbreaks in nearby districts, and have to be taken care of while making any forecasting or disease prediction with other risk factors.

Bluetongue Research at a Crossroads: Modern Genomics Tools Can Pave the Way to New Insights

Bluetongue virus (BTV) is an arthropod-borne, segmented double-stranded RNA virus that can cause severe disease in both wild and domestic ruminants. BTV evolves via several key mechanisms, including the accumulation of mutations over time and the reassortment of genome segments.Additionally, BTV must maintain fitness in two disparate hosts, the insect vector and the ruminant. The specific features of viral adaptation in each host that permit host-switching are poorly characterized. Limited field studies and experimental work have alluded to the presence of these phenomena at work, but our understanding of the factors that drive or constrain BTV's genetic diversification remains incomplete. Current research leveraging novel approaches and whole genome sequencing applications promises to improve our understanding of BTV's evolution, ultimately contributing to the development of better predictive models and management strategies to reduce future impacts of bluetongue epizootics.

Occurrence of Biting Midges (Diptera: Culicoides) on Dairy Farms in Eastern Slovakia in Relation to Abiotic Factors

Within the scope of our research, we have performed 59 trapping sessions and collected 15,756 biting midges from 20 species at four farms (Kluknava, Ostrov, Turňa nad Bodovou and Zemplínska Teplica), The most frequent types of captured insects were representatives of the Avaritia subgenus, C. obsoletus/C. scoticus, representing on average 85.1 % (13,295 individuals) of the fauna of the biting midges, with the exception of the farm in Ostrov where this group represented only 41.7 % of the fauna. At this particular farm, the most frequently trapped insects belonged to the Culicoides subgenus (54.1 %), in particular the C. bysta, C. lupicaris, C. newsteadi, C. Pulicaris and C. Punctatus species. During the trapping sessions, we monitored factors affecting the number of trapped biting midges, such as the temperature, relative air humidity and airflow rate: the air temperature during the trapping of the biting midges ranged from 9.8 to 26.2 °C; the relative air humidity ranged from 35.1 to 100 %; and the air flow rate ranged from no wind to a wind velocity of 8.2 m.s-1. However, in the final evaluation, we failed to observe a statistically significant correlation between the air flow and the number of trapped biting midges. The largest amounts of biting midges were trapped at temperatures ranging from 15.8 to 24.6 °C and at a relative air humidity ranging from 54.2 % to 68.6 %. While monitoring the seasonal dynamics of the physiological conditions of biting midge females at the selected farms, we confirmed that during the period from June to August, the most frequently trapped females were parous (50.1 %; 7,826 individuals). In addition, nulliparous females comprised 43.8 % (6,842 individuals) and were continuously trapped throughout the season (April— November).

High dispersal capacity of Culicoides obsoletus (Diptera: Ceratopogonidae), vector of bluetongue and Schmallenberg viruses, revealed by landscape genetic analyses

BACKGROUND

In the last two decades, recurrent epizootics of bluetongue virus and Schmallenberg virus have been reported in the western Palearctic region. These viruses affect domestic cattle, sheep, goats and wild ruminants and are transmitted by native hematophagous midges of the genus Culicoides (Diptera: Ceratopogonidae). Culicoides dispersal is known to be stratified, i.e. due to a combination of dispersal processes occurring actively at short distances and passively or semi-actively at long distances, allowing individuals to jump hundreds of kilometers.

METHODS

Here, we aim to identify the environmental factors that promote or limit gene flow of Culicoides obsoletus, an abundant and widespread vector species in Europe, using an innovative framework integrating spatial, population genetics and statistical approaches. A total of 348 individuals were sampled in 46 sites in France and were genotyped using 13 newly designed microsatellite markers.

RESULTS

We found low genetic differentiation and a weak population structure for C. obsoletus across the country. Using three complementary inter-individual genetic distances, we did not detect any significant isolation by distance, but did detect significant anisotropic isolation by distance on a north-south axis. We employed a multiple regression on distance matrices approach to investigate the correlation between genetic and environmental distances. Among all the environmental factors that were tested, only cattle density seems to have an impact on C. obsoletus gene flow.

CONCLUSIONS

The high dispersal capacity of C. obsoletus over land found in the present study calls for a re-evaluation of the impact of Culicoides on virus dispersal, and highlights the urgent need to better integrate molecular, spatial and statistical information to guide vector-borne disease control.

Next-generation tools to control biting midge populations and reduce pathogen transmission

Biting midges of the genus Culicoides transmit disease-causing agents resulting in a significant economic impact on livestock industries in many parts of the world. Localized control efforts, such as removal of larval habitat or pesticide application, can be logistically difficult, expensive and ineffective if not instituted and maintained properly. With these limitations, a population-level approach to the management of Culicoides midges should be investigated as a means to replace or supplement existing control strategies. Next-generation control methods such as Wolbachia- and genetic-based population suppression and replacement are being investigated in several vector species. Here we assess the feasibility and applicability of these approaches for use against biting midges. We also discuss the technical and logistical hurdles needing to be addressed for each method to be successful, as well as emphasize the importance of addressing community engagement and involving stakeholders in the investigation and development of these approaches.

Risk-based surveillance for bluetongue virus in cattle on the south coast of England in 2017 and 2018

BACKGROUND

Bluetongue (BT) is a viral disease of ruminants and camelids which can have a significant impact on animal health and welfare and cause severe economic loss. The UK has been officially free of bluetongue virus (BTV) since 2011. In 2015, BTV-8 re-emerged in France and since then BTV has been spreading throughout Europe. In response to this outbreak, risk-based active surveillance was carried out at the end of the vector seasons in 2017 and 2018 to assess the risk of incursion of BTV into Great Britain.

METHOD

Atmospheric dispersion modelling identified counties on the south coast of England at higher risk of an incursion. Blood samples were collected from cattle in five counties based on a sample size designed to detect at least one positive if the prevalence was 5 per cent or greater, with 95 per cent confidence.

RESULTS

No virus was detected in the 478 samples collected from 32 farms at the end of the 2017 vector season or in the 646 samples collected from 43 farms at the end of the 2018 vector season, when tested by RT-qPCR.

CONCLUSION

The negative results from this risk-based survey provided evidence to support the continuation of the UK's official BTV-free status.

Prediction Models in Veterinary and Human Epidemiology: Our Experience With Modeling Sars-CoV-2 Spread

The worldwide outbreak of Sars-CoV-2 resulted in modelers from diverse fields being called upon to help predict the spread of the disease, resulting in many new collaborations between different institutions. We here present our experience with bringing our skills as veterinary disease modelers to bear on the field of human epidemiology, building models as tools for decision makers, and bridging the gap between the medical and veterinary fields. We describe and compare the key steps taken in modeling the Sars-CoV-2 outbreak: criteria for model choices, model structure, contact structure between individuals, transmission parameters, data availability, model validation, and disease management. Finally, we address how to improve on the contingency infrastructure available for Sars-CoV-2.

Culicoides species composition and molecular identification of host blood meals at two zoos in the UK

BACKGROUND

Culicoides biting midges are biological vectors of arboviruses including bluetongue virus (BTV), Schmallenberg virus (SBV) and African horse sickness virus (AHSV). Zoos are home to a wide range of 'at risk' exotic and native species of animals. These animals have a high value both in monetary terms, conservation significance and breeding potential. To understand the risk these viruses pose to zoo animals, it is necessary to characterise the Culicoides fauna at zoos and determine which potential vector species are feeding on which hosts.

METHODS

Light-suction traps were used at two UK zoos: the Zoological Society of London (ZSL) London Zoo (LZ) and ZSL Whipsnade Zoo (WZ). Traps were run one night each week from June 2014 to June 2015. Culicoides were morphologically identified to the species level and any blood-fed Culicoides were processed for blood-meal analysis. DNA from blood meals was extracted and amplified using previously published primers. Sequencing was then carried out to determine the host species.

RESULTS

A total of 11,648 Culicoides were trapped and identified (n = 5880 from ZSL WZ; n = 5768 from ZSL LZ), constituting 25 different species. The six putative vectors of BTV, SBV and AHSV in northern Europe were found at both zoos and made up the majority of the total catch (n = 10,701). A total of 31 host sequences were obtained from blood-fed Culicoides. Culicoides obsoletus/C. scoticus, Culicoides dewulfi, Culicoides parroti and Culicoides punctatus were found to be biting a wide range of mammals including Bactrian camels, Indian rhinoceros, Asian elephants and humans, with Culicoides obsoletus/C. scoticus also biting Darwin's rhea. The bird-biting species, Culicoides achrayi, was found to be feeding on blackbirds, blue tits, magpies and carrion crows.

CONCLUSIONS

To our knowledge, this is the first study to directly confirm blood-feeding of Culicoides on exotic zoo animals in the UK and shows that they are able to utilise a wide range of exotic as well as native host species. Due to the susceptibility of some zoo animals to Culicoides-borne arboviruses, this study demonstrates that in the event of an outbreak of one of these viruses in the UK, preventative and mitigating measures would need to be taken.

Blood-meal analysis of Culicoides (Diptera: Ceratopogonidae) reveals a broad host range and new species records for Romania

BACKGROUND

Culicoides biting midges are potential vectors of different pathogens. However, especially for eastern Europe, there is a lack of knowledge on the host-feeding patterns of this vector group. Therefore, this study aimed to identify Culicoides spp. and their vertebrate hosts collected in a wetland ecosystem.

METHODS

Culicoides spp. were collected weekly from May to August 2017, using Biogents traps with UV light at four sites in the Danube Delta Biosphere Reserve, Romania. Vectors and hosts were identified with a DNA barcoding approach. The mitochondrial cytochrome c oxidase subunit 1 was used to identify Culicoides spp., while vertebrate hosts were determined targeting cytochrome b or 16S rRNA gene fragments. A maximum likelihood phylogenetic tree was constructed to verify the biting midge identity against other conspecific Palaearctic Culicoides species. A set of unfed midges was used for morphological confirmation of species identification using slide-mounted wings.

RESULTS

Barcoding allowed the species identification and detection of corresponding hosts for 1040 (82.3%) of the 1264 analysed specimens. Eight Culicoides spp. were identified with Culicoides griseidorsum, Culicoides puncticollis and Culicoides submaritimus as new species records for Romania. For 39 specimens no similar sequences were found in GenBank. This group of unknown Culicoides showed a divergence of 15.6-16.3% from the closest identified species and clustered in a monophyletic clade, i.e. a novel species or a species without reference sequences in molecular libraries. For all Culicoides spp., nine mammalian and 24 avian species were detected as hosts. With the exception of C. riethi (n = 12), at least one avian host was detected for all Culicoides spp., but this host group only dominated for Culicoides kibunensis and the unknown Culicoides sp.. The most common host group were mammals (n = 993, 87.6% of all identified blood sources) dominated by cattle (n = 817, 70.6%).

CONCLUSIONS

Most Culicoides spp. showed a broad host-feeding pattern making them potential bridge vectors. At the same time, new records of biting midge species for Romania, as well as a potentially unknown Culicoides species, highlight the lack of knowledge regarding the biting midge species and their genetic diversity in eastern Europe.

Laboratory evaluation of stable isotope labeling of Culicoides (Diptera: Ceratopogonidae) for adult dispersal studies

Background

Stable isotope labeling is a promising method for use in insect mark-capture and dispersal studies. Culicoides biting midges, which transmit several important animal pathogens, including bluetongue virus (BTV) and epizootic hemorrhagic disease virus (EHDV), are small flies that develop in various semi-aquatic habitats. Previous Culicoides dispersal studies have suffered from the limitations of other labeling techniques, and an inability to definitively connect collected adult midges to specific immature development sites.

Results

Adult C. sonorensis were successfully labeled with ¹³C and ¹⁵N stable isotopes as larvae developing in a semi-aquatic mud substrate in the laboratory. High and low-dose isotope treatments for both elements significantly enriched midges above the background isotope levels of unenriched controls. Enrichment had no effect on C. sonorensis survival, though a slight (~ 5 day) delay in emergence was observed, and there was no significant effect of pool size on ¹³C or ¹⁵N enrichment levels.

Conclusions

Stable isotope labeling is life-long, and does not interfere with natural insect behaviors. Stable isotope enrichment using ¹³C or ¹⁵N shows promise for Culicoides dispersal studies in the field. This method can be used to identify adult dispersal from larval source habitat where a midge developed. It may be possible to detect a single enriched midge in a pool of unenriched individuals, though further testing is needed to confirm the sensitivity of this method.

Serological evidence of bluetongue virus infection and serotype distribution in dairy cattle in South Korea

Background

Bluetongue is a vector-borne viral disease, and bluetongue virus (BTV) outbreaks can cause substantial economic losses. Even subclinical infection may carry significant associated costs, including a loss of condition, reduced milk yield, and infertility and abortion, and indirect costs, largely due to the export restrictions and surveillance requirements imposed to limit the spread of the virus. However, the BTV epidemiology in the Far East remains incompletely understood, especially in the cattle population in South Korea. In this study, the seroprevalence of BTV antibodies and distribution of BTV serotypes in dairy cattle in South Korea were evaluated to improve the understanding of the BTV epidemiological situation in the Asia-Pacific region.

Results

Between 2012 and 2013, a total of 37 out of 171 dairy cattle herds (21.6%) and 85 out of 466 dairy cattle heads (18.2%) showed antibodies against BTV. Neutralizing antibodies to BTV-1, − 2, − 3, − 4, − 7, − 15, and − 16 serotypes were identified, and the RNAs of the BTV-1, − 2, − 3, − 15, and − 16 serotypes were detected, indicating that BTV was circulating in the dairy cattle population in South Korea.

Conclusions

These findings indicate that BTV is widespread and has circulated in dairy cattle in South Korea. This is the first report presenting evidence of circulating antibodies against BTV and the serotype distribution in bovine populations in South Korea.

Description of the first Schmallenberg disease outbreak in Spain and subsequent virus spreading in domestic ruminants

Schmallenberg disease (SBD) is an emerging disease transmitted mainly among ruminant species by biting midges of the genus Culicoides. Since the Schmallenberg virus (SBV) was first identified in Germany in late 2011, it rapidly spread to other European countries. The aims of the present study were to describe the first SBD outbreak in Spain and to assess the spread and risk factors associated with SBV infection in domestic ruminants from nearby farms during the following year. In March 2012, one malformed stillborn lamb from a sheep farm located in Cordoba province (Southern Spain) was subjected to necropsy. Pathological compatible lesions and molecular analyses confirmed the first SBV infection in Spain. Afterwards, serum samples from 505 extensively reared domestic ruminants from 29 farms were analysed using both blocking ELISA and virus neutralization test against SBV. The overall seroprevalence was 54.4% (CI_95%: 50.0-58.7). Antibodies were detected in 70.6%, 46.0% and 34.8% of cattle, sheep and goats, respectively. A generalized estimating equation model indicated that the main risk factors associated with SBV infection were: species (cattle), age (adult), and absence of animal insecticide treatment. Pathological and molecular results confirmed the presence of SBV in Spain few months after it was firstly identified in Germany. The seroprevalence detected indicates a widespread circulation of SBV in nearby domestic ruminant farms one year after this first outbreak was reported in Spain. Further studies are warranted to determine the spatio-temporal trend of SBV in domestic ruminants in this country.

The effect of temperature, farm density and foot-and-mouth disease restrictions on the 2007 UK bluetongue outbreak

In 2006, bluetongue (BT), a disease of ruminants, was introduced into northern Europe for the first time and more than two thousand farms across five countries were affected. In 2007, BT affected more than 35,000 farms in France and Germany alone. By contrast, the UK outbreak beginning in 2007 was relatively small, with only 135 farms in southeast England affected. We use a model to investigate the effects of three factors on the scale of BT outbreaks in the UK: (1) place of introduction; (2) temperature; and (3) animal movement restrictions. Our results suggest that the UK outbreak could have been much larger had the infection been introduced into the west of England either directly or as a result of the movement of infected animals from southeast England before the first case was detected. The fact that air temperatures in the UK in 2007 were marginally lower than average probably contributed to the UK outbreak being relatively small. Finally, our results indicate that BT movement restrictions are effective at controlling the spread of infection. However, foot-and-mouth disease restrictions in place before the detection and control of BT in 2007 almost certainly helped to limit BT spread prior to its detection.

A cross-sectional serosurvey in a sheep population in central Italy following a bluetongue epidemic

Bluetongue (BT) is a viral disease that affects ruminants and is transmitted by midges of the genus Culicoides spp. The seroprevalence, the clinical form and the occurrence rates significantly differ in relation to several factors such as bluetongue virus (BTV) serotype, host species, breed susceptibility, specific previous exposure, vector ecology, husbandry and health status. Following the 2001-2006 BTV2 and BTV16 epidemics in central Italy, a new epidemic caused by BTV1 occurred in 2013-2015 causing 398 outbreaks in a susceptible population of about 1 million ruminants. The present study assessed the BTV1 seroprevalence in the sheep population of central Italy by conducting two cross-sectional surveys, in the proximity of and within BT outbreak farms. A total of 2,984 sheep from 437 farms were sampled. The animal-level prevalence was 19% (95% CI: 17-21%), the between-herd prevalence was 46% (95% CI: 41-51%) and the within-herd prevalence was 21% (95% CI: 16-26%). Risk factors were investigated by logistic regression models. Living on a farm where an outbreak occurred and the number of outbreaks in proximity of the farm were identified as risk factors, while herd size was identified as a protective factor. This study represents the first BT survey in southern Europe and reports valuable findings on BTV epidemiology. Despite intensive virus circulation, the estimated seroprevalences were low. The assessment of the population immunity level is crucial for defining an efficient vaccination strategy and for predicting the impact of future virus circulation. In view of the low seroprevalence detected albeit an extensive BTV1 circulation, the population immunity was likely to be inadequate in preventing new BTV1 epidemics. Moreover, considering the recurrent introduction of new serotypes from North Africa and the Balkans, the control of multi-serotype BTV infections will continue to present a challenge in the near future.

Retrospective analysis of Bluetongue farm risk profile definition, based on biology, farm management practices and climatic data

Bluetongue (BT) is a vector-borne disease transmitted by species of Culicoides midges (Diptera: Ceratopogonidae). Many studies have contributed to clarifying various aspects of its aetiology, epidemiology and vector dynamic; however, BT remains a disease of epidemiological and economic importance that affects ruminants worldwide. Since 2000, the Sardinia region has been the most affected area of the Mediterranean basin. The region is characterised by wide pastoral areas for sheep and represents the most likely candidate region for the study of Bluetongue virus (BTV) distribution and prevalence in Italy. Furthermore, specific information on the farm level and epidemiological studies needs to be provided to increase the knowledge on the disease's spread and to provide valid mitigation strategies in Sardinia. This study conducted a punctual investigation into the spatial patterns of BTV transmission to define a risk profile for all Sardinian farmsby using a logistic multilevel mixed model that take into account agro-meteorological aspects, as well as farm characteristics and management. Data about animal density (i.e. sheep, goats and cattle), vaccination, previous outbreaks, altitude, land use, rainfall, evapotranspiration, water surface, and farm management practices (i.e. use of repellents, treatment against insect vectors, storage of animals in shelter overnight, cleaning, presence of mud and manure) were collected for 12,277 farms for the years 2011-2015. The logistic multilevel mixed model showed the fundamental role of climatic factors in disease development and the protective role of good management, vaccination, outbreak in the previous year and altitude. Regional BTV risk maps were developed, based on the predictor values of logistic model results, and updated every 10 days. These maps were used to identify, 20 days in advance, the areas at highest risk. The risk farm profile, as defined by the model, would provide specific information about the role of each factor for all Sardinian institutions involved in devising BT prevention and control strategies.

The Role of Culex pipiens L. (Diptera: Culicidae) in Virus Transmission in Europe

Over the past three decades, a range of mosquito-borne viruses that threaten public and veterinary health have emerged or re-emerged in Europe. Mosquito surveillance activities have highlighted the Culex pipiens species complex as being critical for the maintenance of a number of these viruses. This species complex contains morphologically similar forms that exhibit variation in phenotypes that can influence the probability of virus transmission. Critical amongst these is the choice of host on which to feed, with different forms showing different feeding preferences. This influences the ability of the mosquito to vector viruses and facilitate transmission of viruses to humans and domestic animals. Biases towards blood-feeding on avian or mammalian hosts have been demonstrated for different Cx. pipiens ecoforms and emerging evidence of hybrid populations across Europe adds another level of complexity to virus transmission. A range of molecular methods based on DNA have been developed to enable discrimination between morphologically indistinguishable forms, although this remains an active area of research. This review provides a comprehensive overview of developments in the understanding of the ecology, behaviour and genetics of Cx. pipiens in Europe, and how this influences arbovirus transmission.

Quantifying the roles of host movement and vector dispersal in the transmission of vector-borne diseases of livestock

The role of host movement in the spread of vector-borne diseases of livestock has been little studied. Here we develop a mathematical framework that allows us to disentangle and quantify the roles of vector dispersal and livestock movement in transmission between farms. We apply this framework to outbreaks of bluetongue virus (BTV) and Schmallenberg virus (SBV) in Great Britain, both of which are spread by Culicoides biting midges and have recently emerged in northern Europe. For BTV we estimate parameters by fitting the model to outbreak data using approximate Bayesian computation, while for SBV we use previously derived estimates. We find that around 90% of transmission of BTV between farms is a result of vector dispersal, while for SBV this proportion is 98%. This difference is a consequence of higher vector competence and shorter duration of viraemia for SBV compared with BTV. For both viruses we estimate that the mean number of secondary infections per infected farm is greater than one for vector dispersal, but below one for livestock movements. Although livestock movements account for a small proportion of transmission and cannot sustain an outbreak on their own, they play an important role in establishing new foci of infection. However, the impact of restricting livestock movements on the spread of both viruses depends critically on assumptions made about the distances over which vector dispersal occurs. If vector dispersal occurs primarily at a local scale (99% of transmission occurs <25 km), movement restrictions are predicted to be effective at reducing spread, but if dispersal occurs frequently over longer distances (99% of transmission occurs <50 km) they are not.

Diseases which are transmitted by the bites of insects can be spread to new locations through the movement of both infected insects and infected hosts. The importance of these routes has implications for disease control, because we can often restrict host movement, and so potentially reduce spread, but cannot easily restrict insect movements. Despite this, the importance of host movements has been little studied. Here we develop a mathematical model which allows us to disentangle and quantify transmission by insect dispersal and by host movement. We apply the model to two diseases of cattle and sheep transmitted by biting midges that have emerged in northern Europe in the past decade, bluetongue virus (BTV) and Schmallenberg virus (SBV). For both viruses, we show insect movements account for a majority of spread between farms. Although they cannot sustain an epidemic on their own, animal movements play an important role in introducing disease to new areas.

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

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.

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.