Bluetongue, Schmallenberg - what is next? Culicoides-borne viral diseases in the 21st Century

Diversity of biting midges, mosquitoes and sand flies at four dog shelters in rural and peri-urban areas of Central Morocco

Blood-feeding arthropods are involved in the transmission of several pathogens that have a major impact on public health. Entomological investigations highlighted the composition, abundance, and diversity of flying hematophagous arthropods at four dog shelters located in central Morocco during an eight-month study, with the aim of discussing their vectorial roles and assessing the risk of these shelters as foci for zoonotic diseases. Monitoring of the arthropod fauna for 64 catch nights resulted in the collection of 2,321 biting midges (Ceratopogonidae), 570 mosquitoes (Culicidae), and 475 sand flies (Psychodidae). Fourteen Culicoides species were recorded and dominant species were Culicoides imicola (55.96%), C. paolae (16.07%), C. circumscriptus (10.29%), and C. newsteadi (5.77%). Three mosquito species were collected, including Culex pipiens s.l. (96.84%), Culiseta longiareolata (2.80%), and Cx. perexiguus (0.36%). Ten sand fly species were collected, including seven Phlebotomus species (62.70%) and three Sergentomyia species (37.30%); Sergentomyia minuta was the most dominant species (34.31%), followed by Phlebotomus sergenti (32.42%), typical Ph. perniciosus (8.63%), Ph. alexandri (6.94%), and Ph. riouxi (6.52%). The coexistence of several vectors in these study areas indicates the potential circulation of a wide range of pathogens, including zoonotic ones, thus requiring the implementation of surveillance and control programs to prevent the emergence and spread of disease outbreaks.

First molecular evidence of potential Culicoides vectors implicated in bluetongue virus transmission in Morocco

BACKGROUND

Bluetongue is a non-contagious viral disease that affects both domestic and wild ruminants. It is transmitted primarily by small hematophagous Diptera belonging to the genus Culicoides (Diptera: Ceratopogonidae). The current study represents the first molecular investigation into the potential role of Culicoides imicola, Culicoides paolae, Culicoides newsteadi, Culicoides spp., and Culicoides circumscriptus as bluetongue virus (BTV) vectors in Morocco. Additionally, the study aimed to evaluate the vectorial activity of midges during the survey seasons.

METHODS

Parous females of these species were captured from several regions of Morocco (6 out of 12) from 2018 to 2021 using Onderstepoort Veterinary Institute (OVI) traps. A total of 2003 parous female specimens were grouped into 55 batches. The midge body of each batch was dissected into three regions (head, thorax, and abdomen), and these regions were analyzed separately using reverse transcription quantitative polymerase chain reaction (RT-qPCR).

RESULTS

BTV RNA was detected in 45 out of the 55 batches tested, indicating a positivity rate of 81.8%. The RT-qPCR-positive pools of the studied Culicoides species exhibited high levels of BTV positivity in each body part (head, thorax, and abdomen), confirming the successful replication of the virus within midge bodies. The BTV circulation was substantial across all three survey seasons (spring, summer, and autumn). High infection rates, calculated using the minimum infection rate (MIR) and maximum likelihood estimation (MLE), were observed during the collection seasons, particularly in autumn and spring, and for all investigated Culicoides species, most notably for C. imicola and C. newsteadi. These increased infection rates underscore the significant risk of Culicoides transmitting the BTV in Morocco.

CONCLUSIONS

The detection of BTV positivity in Culicoides spp. (lacking wing spots that allow their differentiation according to morphological identification keys) suggested that other Culicoides species are competent for BTV transmission in Morocco. The study results indicated, for the first time at the molecular level, that C. imicola and C. newsteadi are the primary potential vectors of BTV in Morocco and that C. paolae and C. circumscriptus are strongly implicated in the propagation of bluetongue at the national level.

Systematic review of hematophagous arthropods present in cattle in France

The arrival of pathogens, whether zoonotic or not, can have a lasting effect on commercial livestock farms, with dramatic health, social and economic consequences. However, available data concerning the arthropod vectors present and circulating on livestock farms in France are still very imprecise, fragmentary, and scattered. In this context, we conducted a systematic review of the hematophagous arthropod species recorded on different types of cattle farms in mainland France (including Corsica). The used vector "groups" studied were biting flies, biting midges, black flies, fleas, horse flies, lice, louse flies, mosquitoes, sand flies, and ticks. A large number of documents were selected (N = 9,225), read (N = 1,047) and analyzed (N = 290), allowing us to provide distribution and abundance maps of different species of medical and veterinary interest according to literature data. Despite the large number of documents collected and analyzed, there are few data provided on cattle farm characteristics. Moreover, data on all arthropod groups lack numerical detail and are based on limited data in time and/or space. Therefore, they are not generalizable nor comparable. There is still little information on many vectors (and their pathogens) and still many unknowns for most studied groups. It appears necessary to provide new, updated and standardized data, collected in different geographical and climatological areas. Finally, this work highlights the lack of entomologists, funding, training and government support, leading to an increased risk of uncontrolled disease emergence in cattle herds.

Modeling the spatial distribution of Culicoides species (Diptera: Ceratopogonidae) as vectors of animal diseases in Ethiopia

Culicoides biting midges (Diptera: Ceratopogonidae) are the major vectors of bluetongue, Schmallenberg, and African horse sickness viruses. This study was conducted to survey Culicoides species in different parts of Ethiopia and to develop habitat suitability for the major Culicoides species in Ethiopia. Culicoides traps were set in different parts of the country from December 2018 to April 2021 using UV light Onderstepoort traps and the collected Culicoides were sorted to species level. To develop the species distribution model for the two predominant Culicoides species, namely Culicoides imicola and C. kingi, an ensemble modeling technique was used with the Biomod2 package of R software. KAPPA True skill statistics (TSS) and ROC curve were used to evaluate the accuracy of species distribution models. In the ensemble modeling, models which score TSS values greater than 0.8 were considered. Negative binomialregression models were used to evaluate the relationship between C. imicola and C. kingi catch and various environmental and climatic factors. During the study period, a total of 9148 Culicoides were collected from 66 trapping sites. Of the total 9148, 8576 of them belongs to seven species and the remaining 572 Culicoides were unidentified. The predominant species was C. imicola (52.8%), followed by C. kingi (23.6%). The abundance of these two species was highly influenced by the agro-ecological zone of the capture sites and the proximity of the capture sites to livestock farms. Climatic variables such as mean annual minimum and maximum temperature and mean annual rainfall were found to influence the catch of C. imicola at the different study sites. The ensemble model performed very well for both species with KAPPA (0.9), TSS (0.98), and ROC (0.999) for C. imicola and KAPPA (0.889), TSS (0.999), and ROC (0.999) for C. kingi. Culicoides imicola has a larger suitability range compared to C. kingi. The Great Rift Valley in Ethiopia, the southern and eastern parts of the country, and the areas along the Blue Nile and Lake Tana basins in northern Ethiopia were particularly suitable for C. imicola. High suitability for C. kingi was found in central Ethiopia and the Southern Nations, Nationalities and Peoples Region (SNNPR). The habitat suitability model developed here could help researchers better understand where the above vector-borne diseases are likely to occur and target surveillance to high-risk areas.

A Survey on Native and Invasive Mosquitoes and Other Biting Dipterans in Northern Spain

PURPOSE

Haematophagous Diptera, such as mosquitoes (Culicidae), biting midges (Ceratopogonidae), and black flies (Simuliidae), are important insects for public and animal health due to their capacity to bite and transmit pathogens. Outdoor recreation areas are usually affected by biting species and provide suitable habitats to both adult and immature stages. This study aimed to determine the species diversity and larval sites of these Diptera groups in two golf courses.

METHODS

A multi-method collection approach using ultraviolet-CDC traps, human landing catches, collection in breeding sites, and ovitraps was implemented during summer 2020 in northern Spain. Insects were determined by morphological features accompanied by DNA barcoding.

RESULTS

A total of ten native mosquito species were recorded either as adults or as larval stages. The invasive species Aedes japonicus was collected only at egg or pupa stage in ovitraps. Culex pipiens s.l. and Culex torrentium were both common mosquito species accounting for 47.9% of the total larval site collections and their larvae might be found in a wide range of natural and artificial sites. Culiseta longiareolata specimens were also prominent (30.1% of the total) and occurred exclusively in man-made water-filled containers. A total of 13 Culicoides species were identified, 10 of which were captured by ultraviolet-CDC traps, particularly members of the Obsoletus complex (Culicoides obsoletus/Culicoides scoticus, 74.9%) and seven species by emergence traps, being the two most abundant C. kibunensis (44.8%) and C. festivipennis (34.9%). Simulium cryophilum was also collected hovering around the operator under field sampling.

CONCLUSION

A comprehensive representation of the blood-sucking Diptera fauna and their larval sites was obtained by the multi-method approach in two Spanish golf courses.

Assessing the introduction risk of vector-borne animal diseases for the Netherlands using MINTRISK: A Model for INTegrated RISK assessment

To evaluate and compare the risk of emerging vector-borne diseases (VBDs), a Model for INTegrated RISK assessment, MINTRISK, was developed to assess the introduction risk of VBDs for new regions in an objective, transparent and repeatable manner. MINTRISK is a web-based calculation tool, that provides semi-quantitative risk scores that can be used for prioritization purposes. Input into MINTRISK is entered by answering questions regarding entry, transmission, establishment, spread, persistence and impact of a selected VBD. Answers can be chosen from qualitative answer categories with accompanying quantitative explanation to ensure consistent answering. The quantitative information is subsequently used as input for the model calculations to estimate the risk for each individual step in the model and for the summarizing output values (rate of introduction; epidemic size; overall risk). The risk assessor can indicate his uncertainty on each answer, and this is accounted for by Monte Carlo simulation. MINTRISK was used to assess the risk of four VBDs (African horse sickness, epizootic haemorrhagic disease, Rift Valley fever, and West Nile fever) for the Netherlands with the aim to prioritise these diseases for preparedness. Results indicated that the overall risk estimate was very high for all evaluated diseases but epizootic haemorrhagic disease. Uncertainty intervals were, however, wide limiting the options for ranking of the diseases. Risk profiles of the VBDs differed. Whereas all diseases were estimated to have a very high economic impact once introduced, the estimated introduction rates differed from low for Rift Valley fever and epizootic haemorrhagic disease to moderate for African horse sickness and very high for West Nile fever. Entry of infected mosquitoes on board of aircraft was deemed the most likely route of introduction for West Nile fever into the Netherlands, followed by entry of infected migratory birds.

Culicoides biting midges and mosquito fauna at three dog and cat shelters in rural and periurban areas in Northern Spain

The diversity and abundance of Culicoides (Diptera: Ceratopogonidae) and mosquitoes (Diptera: Culicidae) were studied in three animal protection centres (APCs) in Northern Spain between 1 July and 31 October 2018. Four miniature suction CDC light traps (two UV and two standard incandescent bulb traps, both types baited and non-baited with CO₂ ) were placed in each APC to compare their efficiency in the collection of these Diptera groups. A total of 1176 biting midges (14 species), 224 mosquitoes (8 species) and 1 black fly were collected and identified by both morphological and molecular approaches. The Culicoides obsoletus complex (C. obsoletus/C. scoticus) accounted for 58.2% of the total collection within the Ceratopogonidae family, whereas Culex pipiens/Cx. torrentium comprised 76.8% of the Culicidae. The input of CO₂ in light traps proved largely ineffective in improving the collections of both Diptera groups. UV-light traps were 7.8 and 2.2 times more effective than incandescent light traps in trapping Culicoides and mosquitoes, respectively. Seasonal dynamics differed between both Diptera taxa but captures of both taxa were significantly larger at the beginning of the summer. The epidemiological relevance of the most prevalent species is also discussed.

Biting midge dynamics and bluetongue transmission: a multiscale model linking catch data with climate and disease outbreaks

Bluetongue virus (BTV) serotype 8 has been circulating in Europe since a major outbreak occurred in 2006, causing economic losses to livestock farms. The unpredictability of the biting activity of midges that transmit BTV implies difficulty in computing accurate transmission models. This study uniquely integrates field collections of midges at a range of European latitudes (in Sweden, The Netherlands, and Italy), with a multi-scale modelling approach. We inferred the environmental factors that influence the dynamics of midge catching, and then directly linked predicted midge catches to BTV transmission dynamics. Catch predictions were linked to the observed prevalence amongst sentinel cattle during the 2007 BTV outbreak in The Netherlands using a dynamic transmission model. We were able to directly infer a scaling parameter between daily midge catch predictions and the true biting rate per cow per day. Compared to biting rate per cow per day the scaling parameter was around 50% of 24 h midge catches with traps. Extending the estimated biting rate across Europe, for different seasons and years, indicated that whilst intensity of transmission is expected to vary widely from herd to herd, around 95% of naïve herds in western Europe have been at risk of sustained transmission over the last 15 years.

Thermal limits for flight activity of field-collected Culicoides in the United Kingdom defined under laboratory conditions

BACKGROUND

Culicoides biting midges (Diptera: Ceratopogonidae) are biological vectors of internationally important arboviruses and inflict biting nuisance on humans, companion animals and livestock. In temperate regions, transmission of arboviruses is limited by temperature thresholds, in both replication and dissemination of arboviruses within the vector and in the flight activity of adult Culicoides. This study aims to determine the cold-temperature thresholds for flight activity of Culicoides from the UK under laboratory conditions.

METHODS

Over 18,000 Culicoides adults were collected from the field using 4 W down-draught miniature ultraviolet Centers for Disease Control traps. Populations of Culicoides were sampled at three different geographical locations within the UK during the summer months and again in the autumn at one geographical location. Activity at constant temperatures was assessed using a bioassay that detected movement of adult Culicoides towards an ultraviolet light source over a 24-h period.

RESULTS

The proportion of active adult Culicoides increased with temperature but cold temperature thresholds for activity varied significantly according to collection season and location. Populations dominated by the subgenus Avaritia collected in South East England had a lower activity threshold temperature in the autumn (4 °C) compared with populations collected in the summer (10 °C). Within the subgenus Avaritia, Culicoides scoticus was significantly more active across all temperatures tested than Culicoides obsoletus within the experimental setup. Populations of Culicoides impunctatus collected in the North East of England were only active once temperatures reached 14 °C. Preliminary data suggested flight activity of the subgenus Avaritia does not differ between populations in South East England and those in the Scottish Borders.

CONCLUSIONS

These findings demonstrate seasonal changes in temperature thresholds for flight and across different populations of Culicoides. These data, alongside that defining thresholds for virus replication within Culicoides, provide a primary tool for risk assessment of arbovirus transmission in temperate regions. In addition, the study also provides a comparison with thermal limits derived directly from light-suction trapping data, which is currently used as the main method to define adult Culicoides activity during surveillance.

Identification and Characterization of Bluetongue Virus Serotype 14 in Russia

This paper reports a case of bluetongue virus (BTV) infection in the Smolensk and Kaluga regions of Russia in 2011-2012. The virus was initially detected in heifers transferred in Russia from Germany through Poland and Belarus in 2011. On day 27 of quarantine, RNA and infectious viruses of BTV were detected in four heifers, but five were serologically positive. However, on day 3 before shipment, all heifers were seronegative and PCR-negative for BTV. Thus, a few animals from this consignment were viremic without any evident subclinical infection. Based on Seg-2 (VP2 gene) and Seg-5 (NS1 gene) sequencing, the recovered virus had 99.86-100% nucleotide identity with BTV-14-like viruses such as the vaccine BTV-14 strain RSArrrr/BTV 14 and the BTV-14 isolates detected in Lithuania and Poland in 2012. Subsequently, BTV-14 was also reported in local animals in two regions of Russia. During the monitoring survey, 1623 local animals within a 300-km radius were tested, of which 471 tested positive by ELISA and 183 by PCR for BTV-14 RNA. No other serotypes were identified in either imported or aboriginal animals within that radius. The Culicoides midges trapped at the site of the outbreak in May 2012 tested positive for the BTV-14 genome, indicating that the possible mechanism of spread most likely occurs via vector bites. However, further investigation is required to confirm this hypothesis, which would provide an improved understanding of the circulation and overwintering of BTV in northern latitudes.

GENETIC RELATEDNESS OF EPIZOOTIC HEMORRHAGIC DISEASE VIRUS SEROTYPE 2 FROM 2012 OUTBREAK IN THE USA

During summer and early fall of 2012, the US experienced the largest outbreak of hemorrhagic disease (HD) on record; deer (both Odocoileus virginianus and Odocoileus hemionus) in 35 states were affected, including many northern states where HD typically does not occur. Epizootic hemorrhagic disease virus (EHDV) was the predominant virus isolated, with serotype 2 (EHDV-2) representing 66% (135/205) of all isolated viruses. Viruses within the EHDV serogroup are genetically similar, but we hypothesized that subtle genetic distinctions between viruses would exist across the geographic range of the outbreak if multiple EHDV-2 strains were responsible. We examined viral relatedness and molecular epidemiology of the outbreak by sequencing the mammalian binding protein (VP2) gene and the insect vector binding protein (VP7) gene of 34 EHDV-2 isolates from 2012 across 21 states. Nucleotide sequences of VP2 had 99.0% pairwise identity; VP7 nucleotide sequences had 99.1% pairwise identity. Very few changes were observed in either protein at the amino acid level. Despite the high genetic similarity between isolates, subtle nucleotide differences existed. Both VP2 and VP7 gene sequences separated into two distinct clades based on patterns of single-nucleotide polymorphisms after phylogenetic analysis. The clades were divided geographically into eastern and western clades, although those divisions were not identical between VP2 and VP7. There was also an association between percent sequence identity and geographic distance between isolates. We concluded that multiple EHDV-2 strains contributed to this outbreak.

Community analysis of the abundance and diversity of biting midge species (Diptera: Ceratopogonidae) in three European countries at different latitudes

BACKGROUND

The outbreaks of bluetongue and Schmallenberg disease in Europe have increased efforts to understand the ecology of Culicoides biting midges and their role in pathogen transmission. However, most studies have focused on a specific habitat, region, or country. To facilitate wider comparisons, and to obtain a better understanding of the spread of disease through Europe, the present study focused on monitoring biting midge species diversity in three different habitat types and three countries across Europe.

METHODS

Biting midges were trapped using Onderstepoort Veterinary Institute light traps at a total of 27 locations in Sweden, the Netherlands and Italy, comprising farm, peri-urban and wetland habitats. From July 2014 to June 2015 all locations were sampled monthly, except for during the winter months. Trapped midges were counted and identified morphologically. Indices on species richness, evenness and diversity were calculated. Community compositions were analysed using non-metric multidimensional scaling (NMDS) techniques.

RESULTS

A total of 50,085 female midges were trapped during 442 collection nights. More than 88% of these belonged to the Obsoletus group. The highest midge diversity was found in Sweden, while species richness was highest in the Netherlands, and most specimens were trapped in Italy. For habitats within countries, diversity of the trapped midges was lowest for farms in all countries. Differences in biting midge species communities were more distinct across the three countries than the three habitat types.

CONCLUSIONS

A core midge community could be identified, in which the Obsoletus group was the most abundant. Variations in vector communities across countries imply different patterns of disease spread throughout Europe. How specific species and their associated communities affect disease risk is still unclear. Our results emphasize the importance of midge diversity data at community level, how this differs across large geographic range within Europe, and its implications on assessing risks of midge-borne disease outbreaks.

Genetically stable infectious Schmallenberg virus persists in foetal envelopes of pregnant ewes

Schmallenberg virus (SBV) is a recently emerged vector-borne virus, inducing congenital defects in bovines, ovines and caprines. Here we have shown that infectious SBV is capable of persisting until the moment of birth in the foetal envelopes of ewes infected with SBV-infectious serum at day 45 (1/5 positive) and 60 (4/6 positive) of gestation. This persistence of at least 100 days is a new aspect of the SBV pathogenesis that could help to explain how SBV overwinters the cold season in temperate climate zones. Furthermore, sequencing of the M segment shows that the persisting virus in the foetal envelopes is genetically stable since only a few mutations compared to the inoculum were found. This supports the hypothesis that persisting virus could start the infection of new hosts. Finally, neutralization tests showed that infectious SBV present in the foetal envelopes at birth can be neutralized by the humoral immunity present in the infected ewes.

Role of different Culicoides vectors (Diptera: Ceratopogonidae) in bluetongue virus transmission and overwintering in Sardinia (Italy)

Background

Bluetongue (BT) epidemics have affected the Mediterranean island of Sardinia since 2000. While Culicoides imicola represents the main bluetongue virus (BTV) vector, other European Culicoides biting midges, possibly implicated in virus transmission, have been detected here. Understanding their distribution, seasonal abundance, and infection rates is necessary to predict disease incidence and spread across coastal and inland areas, and to define their role in virus overwintering.

Methods

Biting midge abundance was determined by light traps on selected farms representing diverse climatic conditions of Sardinia. Livestock-associated Culicoides species were morphologically and molecularly identified. Infection rates in prevailing midge species captured in 2013 during a BTV-1 outbreak were determined using RT-qPCR based virus detection in insect body pools, supplemented by specific body region analyses. The seasonal infection prevalence in Culicoides samples collected in 2001 in a BTV-2 affected farm was also determined.

Results

The Newsteadi complex (C. newsteadi species A and species B) prevailed among all biting midge species (47.7 %), followed by C. imicola (27.8 %) and the Obsoletus complex (C. obsoletus and C. scoticus) (17.6 %). Whilst Culicoides imicola was more abundant along the coast, the Newsteadi complex was frequently collected at higher altitude and the Obsoletus complex was notably associated to cattle farms. Culicoides pulicaris and C. punctatus abundance was found to be marginal in all farms. BTV was detected in parous female samples of all these species, and the full dissemination of the virus within the body of C. imicola, C. obsoletus, C. scoticus, and Newsteadi complex species was confirmed by analyses of thorax and head, containing salivary glands. Higher infection rates were associated with C. scoticus, C. newsteadi species A and species B, compared to C. imicola. The virus was detected in C. newsteadi species A and C. obsoletus in winter and spring, whereas it was mainly found in summer and autumn in C. imicola.

Conclusions

In Sardinia, bluetongue virus is transmitted by multiple Culicoides vectors, including C. imicola and the Newsteadi complex being the most important. The Newsteadi complex and other midge species can play an important role in internal areas and are likely to be directly involved in virus overwintering.

Outdoor and indoor monitoring of livestock-associated Culicoides spp. to assess vector-free periods and disease risks

Background

Within the last few decades Culicoides spp. (Diptera: Ceratopogonidae) emerged Europe-wide as a major vector for epizootic viral diseases e.g. caused by Bluetongue (BT) or Schmallenberg virus. In accordance with the EU regulation 1266/2007, veterinary authorities are requested to determine vector-free periods for loosing trade and movement restrictions of susceptible livestock. Additionally, the widely used basic reproduction number \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\mathcal {R}_{0}$\end{document}R0 is optionally applied for risk assessment of vector-borne diseases. Values of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\mathcal {R}_{0}<1$\end{document}R0<1 indicate periods with no disease transmission risk. For the determination of vector-free period and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\mathcal {R}_{0}$\end{document}R0 a continuously operating daily Culicoides spp. monitoring in Vienna (Austria) was established. It covered the period 2009–2013 and depicts the seasonal vector abundance indoor and outdoor. Future BT and African horse sickness (AHS) outbreak risks were estimated by projecting \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\mathcal {R}_{0}$\end{document}R0 to climate change scenarios. Therefore, temperature-dependent vector parameters were applied.

Results

The vector-free period lasted about 100 days inside stables, while less than five Culicoides were trapped outdoors on 150 days per season, i.e. winter half year. Additionally, the potential outbreak risk was assessed for BT and AHS. For BT, a basic reproduction number of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\mathcal {R}_{0}>1$\end{document}R0>1 was found each year between June and August. The periods without transmission risk, i.e. \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\mathcal {R}_{0}<1$\end{document}R0<1, were notably higher (200 days). Contrary, values of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\mathcal {R}_{0}<1$\end{document}R0<1 were estimated for AHS during the whole period. Finally, the basic reproduction numbers were projected to the future by using temperature forecasts for the period 2014–2100. While the mean summer peak values for BT increase from of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\mathcal {R}_{0}=2.3$\end{document}R0=2.3 to \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\mathcal {R}_{0}=3.4$\end{document}R0=3.4 until 2100 (1.1/100 years), no risk for AHS was estimated even under climate warming assumptions.

Conclusions

Restrictions to trade and movement are always associated with an economic impact during epidemic diseases. To minimize these impacts, risk assessments based on the vector-free period or the basic reproduction number \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\mathcal {R}_{0}$\end{document}R0 can essentially support veterinary authorities to improve protection and control measurements.

Persistence of the protective immunity and kinetics of the isotype specific antibody response against the viral nucleocapsid protein after experimental Schmallenberg virus infection of sheep

Schmallenberg virus (SBV) is an Orthobunyavirus that induces abortion, stillbirths and congenital malformations in ruminants. SBV infection induces a long lasting seroconversion under natural conditions. The persistence of the protective immunity and the isotype specific antibody response upon SBV infection of sheep has however not been studied in detail. Five sheep were kept in BSL3 facilities for more than 16 months and subjected to repeated SBV infections. Blood was regularly sampled and organs were collected at euthanasia. The presence of SBV RNA in serum and organs was measured with quantitative real-time PCR. The appearance and persistence of neutralizing and SBV nucleoprotein (N) isotype specific antibodies was determined with virus neutralization tests (VNT) and ELISAs. The primo SBV infection protected ewes against clinical signs, viraemia and virus replication in organs upon challenge infections more than 15 months later. Production of neutralizing SBV specific antibodies was first detected around 6 days post primo-inoculation with VNT and correlated with the appearance of SBV-N specific IgM antibodies. These IgM antibodies remained present for 2 weeks. SBV-N specific IgG antibodies were first detected between 10 and 21 dpi and reached a plateau at 28 dpi. This plateau remained consistently high and no significant decrease in titre was found over a period of more than 1 year. Similar results were found for the neutralising antibody response. In conclusion, the SBV specific IgM response probably eliminates SBV from the blood and the protective immunity induced by SBV infection protects sheep against reinfection for at least 16 months.

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.

Bluetongue in small ruminants: An opinionated review, with a brief appraisal of the 2014 outbreak of the disease in Greece and the south-east Europe

Bluetongue is an arthropod-borne viral disease of ruminants, especially of sheep, caused by Bluetongue virus, which belongs to the genus Orbivirus of the family Reoviridae and is classified into 26 antigenically distinct serotypes. Once thought to be restricted in Africa and parts of the Middle East, bluetongue has now become a concern in sheep-rearing countries around the world. In the past 10 years, severe outbreaks have occurred in Europe with important economic consequences; of these, the 2006-20008 outbreak in Europe was caused by a serotype 8 strain and the 2014 outbreak in Greece and the other countries of south-east Europe was caused by a serotype 4 strain, suggested to be a reassortant strain with genome segments from lineages of serotype 1, 2 and 4. Immunisation campaigns can be implemented for successful control and limiting of the disease. Nevertheless, in both of the above outbreaks, late application of vaccinations led to a wide spread of the disease, which subsequently resulted in significant losses in livestock in the affected regions. In view of that, standardisation of control measures in the future will be beneficial for efficiently limiting outbreaks of the disease.

Schmallenberg virus infection of ruminants: challenges and opportunities for veterinarians

In 2011, European ruminant flocks were infected by Schmallenberg virus (SBV) leading to transient disease in adult cattle but abortions and congenital deformities in calves, lambs, and goat kids. SBV belonging to the Simbu serogroup (family Bunyaviridae and genus Orthobunyavirus) was first discovered in the same region where bluetongue virus serotype 8 (BTV-8) emerged 5 years before. Both viruses are transmitted by biting midges (Culicoides spp.) and share several similarities. This paper describes the current knowledge of temporal and geographical spread, molecular virology, transmission and susceptible species, clinical signs, diagnosis, prevention and control, impact on ruminant health, and productivity of SBV infection in Europe, and compares SBV infection with BTV-8 infection in ruminants.

The Role of microRNAs in Bovine Infection and Immunity

MicroRNAs (miRNAs) are a class of small, non-coding RNAs that are recognized as critical regulators of immune gene expression during infection. Many immunologically significant human miRNAs have been found to be conserved in agriculturally important species, including cattle. Discovering how bovine miRNAs mediate the immune defense during infection is critical to understanding the etiology of the most prevalent bovine diseases. Here, we review current knowledge of miRNAs in the bovine genome, and discuss the advances in understanding of miRNAs as regulators of immune cell function, and bovine immune response activation, regulation, and resolution. Finally, we consider the future perspectives on miRNAs in bovine viral disease, their role as potential biomarkers and in therapy.