Bluetongue: control, surveillance and safe movement of animals

Assessing the export trade risk of bluetongue virus serotypes 4 and 8 in France

Bluetongue (BT) causes an economic loss of $3 billion every year in the world. After two serious occurrences of BT (bluetongue virus [BTV] occurrence in 2006 and 2015), France has been controlling for decades, but it has not been eradicated. As the largest live cattle export market in the world, France is also one of the major exporters of breeding animals and genetic materials in the world. The biosafety of its exported cattle and products has always been a concern. The scenario tree quantitative model was used to analyze the risk of BTV release from French exported live cattle and bovine semen. The results showed that with the increase in vaccination coverage rates, the risk decreased. If the vaccine coverage is 0%, the areas with the highest average risk probability of BTV-4 and BTV-8 release from exported live cattle were Haute-Savoie and Puy-de-Dôme, and the risk was 2.96 × 10^-4 and 4.25 × 10^-4 , respectively. When the vaccine coverage was 90%, the risk probability of BTV-4 and BTV-8 release from exported live cattle was 2.96 × 10^-5 and 4.24 × 10^-5 , respectively. The average probability of BTV-8 release from bovine semen was 1.09 × 10^-10 . Sensitivity analysis showed that the probability of false negative polymerase chain reaction (PCR) test and the probability of BT infection in the bull breeding station had an impact on the model. The identification of high-risk areas and the discovery of key control measures provide a reference for decision makers to assess the risk of French exports of live cattle and bovine semen.

Serological and molecular prevalence study of bluetongue virus in small domestic ruminants in Morocco

Bluetongue is an arthropod-borne viral disease transmitted by Culicoides biting midges, affecting domestic and wild ruminants. The current study aims to assess the seroprevalence of the bluetongue virus (BTV) and confirm its active circulation among sheep and goats populations in Morocco, as well as study the risk factors associated with BTV infection. To this end, a total of 1651 samples were randomly collected from 1376 sheep and 275 goats in eight (out of 12) regions of the country between March 2018 and July 2021.These samples were primarily tested using competitive ELISA (c-ELISA). Subsequently, 65% of c-ELISA positives (n = 452) were analyzed by real-time reverse transcription-polymerase chain reaction (RT-qPCR). The results revealed an overall BTV seroprevalence in small ruminants in Morocco of 41.7%, including 42.6% in sheep and 37.5% in goats. The RT-qPCR results showed that the overall BTV viropositivity rate was 46.7%, including 48.1% in sheep and 41.8% in goats. These viro-serological rates varied significantly by age, sex, and breed of the tested animals, husbandry method, season, and geographic origin. This indicates that these parameters constitute risk factors for BTV transmission routes in Morocco. The findings also indicate that goats play a role as reservoirs in maintaining the BTV in Morocco. It appears from this study that bluetongue is endemic in Morocco. The environmental and climate conditions as well as the husbandry methods adopted in the country are particularly favorable for the virus transmission throughout the country.

Bluetongue Virus Infections in Cattle Herds of Manabí Province of Ecuador

Bluetongue (BT) is a viral disease transmitted by Culicoides (Diptera: Ceratopogonidae) to domestic and wild ruminants. Infections in cattle are mainly subclinical, but severe necrotic and hemorrhagic illness and death may occur depending on the strain of the virus and other factors; cattle act as a reservoir for the virus. Although the Ecuadorian coast has climatic conditions that favor the presence of the vector, there are few serologic or virologic BTV studies available. Manabí is a coastal province in which livestock farming is mostly implemented in the northern part. We conducted two studies to assess, for the first time, the presence of active BTV infections in Manabí province. We collected 430 serum samples from 38 randomly selected farms between March and July 2019 to perform BTV competitive ELISA. In addition, six seropositive farms were selected to place eight sentinel BTV-naive calves. All these calves were blood sampled and the presence of BTV RNA and antibodies was tested for by RT-PCR and competitive ELISA, respectively, once a week for 6-8 weeks until seroconversion was evidenced. A high individual seroprevalence (99%) was obtained, and all investigated farms had BTV seropositive animals. All sentinel calves became BTV viremic and seroconverted. The first viremia appeared after 2-5 weeks from arrival at the farm; they seroconverted 1-3 weeks later. We demonstrate for the first time that there is a high level of BTV circulation north of Manabí, with active infections on these farms. Integrated control strategies such as hygienic measures on farms to reduce midge populations would be advisable for the owners as mitigation measures.

An updated review on bluetongue virus: epidemiology, pathobiology, and advances in diagnosis and control with special reference to India

Bluetongue (BT) is an economically important, non-contagious viral disease of domestic and wild ruminants. BT is caused by BT virus (BTV) and it belongs to the genus Orbivirus and family Reoviridae. BTV is transmitted by Culicoides midges and causes clinical disease in sheep, white-tailed deer, pronghorn antelope, bighorn sheep, and subclinical manifestation in cattle, goats and camelids. BT is a World Organization for Animal Health (OIE) listed multispecies disease and causes great socio-economic losses. To date, 28 serotypes of BTV have been reported worldwide and 23 serotypes have been reported from India. Transplacental transmission (TPT) and fetal abnormalities in ruminants had been reported with cell culture adopted live-attenuated vaccine strains of BTV. However, emergence of BTV-8 in Europe during 2006, confirmed TPT of wild-type/field strains of BTV. Diagnosis of BT is more important for control of disease and to ensure BTV-free trade of animals and their products. Reverse transcription polymerase chain reaction, agar gel immunodiffusion assay and competitive enzyme-linked immunosorbent assay are found to be sensitive and OIE recommended tests for diagnosis of BTV for international trade. Control measures include mass vaccination (most effective method), serological and entomological surveillance, forming restriction zones and sentinel programs. Major hindrances with control of BT in India are the presence of multiple BTV serotypes, high density of ruminant and vector populations. A pentavalent inactivated, adjuvanted vaccine is administered currently in India to control BT. Recombinant vaccines with DIVA strategies are urgently needed to combat this disease. This review is the first to summarise the seroprevalence of BTV in India for 40 years, economic impact and pathobiology.

The threat of veterinary medicinal products and biocides on pollinators: A One Health perspective

The One Health approach acknowledges that human health is firmly linked to animal and environmental health. It involves using animals such as bees and other pollinators as sentinels for environmental contamination or biological indicators. Beekeepers noticed intoxications of apiaries located in the vicinity of sheep and cattle farms, which led to the suspicion of bees' intoxication by the products used for livestock: veterinary medicinal products (VMPs) and Biocides, confirmed by laboratory analysis. We review the legal context of VMPs and Biocidal products considering Europe as a case study, and identify shortcomings at the environmental level. We describe the possible ways these products could intoxicate bees in the vicinity of livestock farms. We also illustrate the way they may impact non-target species. The cases of ivermectin and abamectin as VMPs, deltamethrin and permethrin as Biocides are considered as case studies. We show bees can be exposed to new and unrecognized routes of exposure to these chemicals, and demonstrate that their application in livestock farming can affect the survival of pollinators, such as bees. We conclude that: (1) figures on the marketing/use of these chemicals should be harmonized, centralized and publicly available, (2) research should be devoted to clarifying how pollinators are exposed to VMPs and Biocides, (3) toxicity studies on bees should be carried out, and (4) pollinators should be considered as non-targeted species concerning the environmental risk assessment before their marketing authorization. We propose the term "Multi-use substances" for active ingredients with versatile use.

Scientific Opinion on the assessment of the control measures of the category A diseases of Animal Health Law: African Horse Sickness

EFSA received a mandate from the European Commission to assess the effectiveness of some of the control measures against diseases included in the Category A list according to Regulation (EU) 2016/429 on transmissible animal diseases (‘Animal Health Law’). This opinion belongs to a series of opinions where these control measures will be assessed, with this opinion covering the assessment of control measures for African Horse Sickness (AHS). In this opinion, EFSA and the AHAW Panel of experts review the effectiveness of: (i) clinical and laboratory sampling procedures, (ii) monitoring period and (iii) the minimum radius of the protection and surveillance zone, and the minimum duration of measures in these zones. The general methodology used for this series of opinions has been published elsewhere; nonetheless, specific details of the transmission kernels used for the assessment of the minimum radius of the protection and surveillance zones are shown. Several scenarios for which these control measures were assessed were designed and agreed prior to the start of the assessment. In summary, sampling procedures described in the diagnostic manual for AHS were considered efficient for all Equidae considering the high case fatality rate expected. The monitoring period (14 days) was assessed as effective in every scenario, except for those relating to the epidemiological enquiry where the risk manager should consider increasing the monitoring period, based on the awareness of keepers, environmental conditions and the vector abundance in the region. The current protection zone (100 km) comprises more than 95% of the infections from an affected establishment. Both the radius and duration of the zones could be reduced, based on local environmental conditions and the time of year of the first index case. Recommendations provided for each of the scenarios assessed aim to support the European Commission in the drafting of further pieces of legislation relating to AHS.

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.

Identifying Spanish Areas at More Risk of Monthly BTV Transmission with a Basic Reproduction Number Approach

Bluetongue virus (BTV) causes a disease that is endemic in Spain and its two major biological vector species, C. imicola and the Obsoletus complex species, differ greatly in their ecology and distribution. Understanding the seasonality of BTV transmission in risk areas is key to improving surveillance and control programs, as well as to better understand the pathogen transmission networks between wildlife and livestock. Here, monthly risk transmission maps were generated using risk categories based on well-known BTV R0 equations and predicted abundances of the two most relevant vectors in Spain. Previously, Culicoides spp. predicted abundances in mainland Spain and the Balearic Islands were obtained using remote sensing data and random forest machine learning algorithm. Risk transmission maps were externally assessed with the estimated date of infection of BTV-1 and BTV-4 historical outbreaks. Our results highlight the differences in risk transmission during April-October, June-August being the period with higher R0 values. Likewise, a natural barrier has been identified between northern and central-southern areas at risk that may hamper BTV spread between them. Our results can be relevant to implement risk-based interventions for the prevention, control and surveillance of BTV and other diseases shared between livestock and wildlife host populations.

Bayesian optimisation of restriction zones for bluetongue control

We investigate the restriction of animal movements as a method to control the spread of bluetongue, an infectious disease of livestock that is becoming increasingly prevalent due to the onset of climate change. We derive control policies for the UK that minimise the number of infected farms during an outbreak using Bayesian optimisation and a simulation-based model of BT. Two cases are presented: first, where the region of introduction is randomly selected from England and Wales to find a generalised strategy. This “national” model is shown to be just as effective at subduing the spread of bluetongue as the current strategy of the UK government. Our proposed controls are simpler to implement, affect fewer farms in the process and, in so doing, minimise the potential economic implications. Second, we consider policies that are tailored to the specific region in which the first infection was detected. Seven different regions in the UK were explored and improvements in efficiency from the use of specialised policies presented. As a consequence of the increasing temperatures associated with climate change, efficient control measures for vector-borne diseases such as this are expected to become increasingly important. Our work demonstrates the potential value of using Bayesian optimisation in developing cost-effective disease management strategies.

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.

Monthly variation in the probability of presence of adult Culicoides populations in nine European countries and the implications for targeted surveillance

BACKGROUND

Biting midges of the genus Culicoides (Diptera: Ceratopogonidae) are small hematophagous insects responsible for the transmission of bluetongue virus, Schmallenberg virus and African horse sickness virus to wild and domestic ruminants and equids. Outbreaks of these viruses have caused economic damage within the European Union. The spatio-temporal distribution of biting midges is a key factor in identifying areas with the potential for disease spread. The aim of this study was to identify and map areas of neglectable adult activity for each month in an average year. Average monthly risk maps can be used as a tool when allocating resources for surveillance and control programs within Europe.

METHODS

We modelled the occurrence of C. imicola and the Obsoletus and Pulicaris ensembles using existing entomological surveillance data from Spain, France, Germany, Switzerland, Austria, Denmark, Sweden, Norway and Poland. The monthly probability of each vector species and ensembles being present in Europe based on climatic and environmental input variables was estimated with the machine learning technique Random Forest. Subsequently, the monthly probability was classified into three classes: Absence, Presence and Uncertain status. These three classes are useful for mapping areas of no risk, areas of high-risk targeted for animal movement restrictions, and areas with an uncertain status that need active entomological surveillance to determine whether or not vectors are present.

RESULTS

The distribution of Culicoides species ensembles were in agreement with their previously reported distribution in Europe. The Random Forest models were very accurate in predicting the probability of presence for C. imicola (mean AUC = 0.95), less accurate for the Obsoletus ensemble (mean AUC = 0.84), while the lowest accuracy was found for the Pulicaris ensemble (mean AUC = 0.71). The most important environmental variables in the models were related to temperature and precipitation for all three groups.

CONCLUSIONS

The duration periods with low or null adult activity can be derived from the associated monthly distribution maps, and it was also possible to identify and map areas with uncertain predictions. In the absence of ongoing vector surveillance, these maps can be used by veterinary authorities to classify areas as likely vector-free or as likely risk areas from southern Spain to northern Sweden with acceptable precision. The maps can also focus costly entomological surveillance to seasons and areas where the predictions and vector-free status remain uncertain.

Spatial and temporal variation in the abundance of Culicoides biting midges (Diptera: Ceratopogonidae) in nine European countries

BACKGROUND

Biting midges of the genus Culicoides (Diptera: Ceratopogonidae) are vectors of bluetongue virus (BTV), African horse sickness virus and Schmallenberg virus (SBV). Outbreaks of both BTV and SBV have affected large parts of Europe. The spread of these diseases depends largely on vector distribution and abundance. The aim of this analysis was to identify and quantify major spatial patterns and temporal trends in the distribution and seasonal variation of observed Culicoides abundance in nine countries in Europe.

METHODS

We gathered existing Culicoides data from Spain, France, Germany, Switzerland, Austria, Denmark, Sweden, Norway and Poland. In total, 31,429 Culicoides trap collections were available from 904 ruminant farms across these countries between 2007 and 2013.

RESULTS

The Obsoletus ensemble was distributed widely in Europe and accounted for 83% of all 8,842,998 Culicoides specimens in the dataset, with the highest mean monthly abundance recorded in France, Germany and southern Norway. The Pulicaris ensemble accounted for only 12% of the specimens and had a relatively southerly and easterly spatial distribution compared to the Obsoletus ensemble. Culicoides imicola Kieffer was only found in Spain and the southernmost part of France. There was a clear spatial trend in the accumulated annual abundance from southern to northern Europe, with the Obsoletus ensemble steadily increasing from 4000 per year in southern Europe to 500,000 in Scandinavia. The Pulicaris ensemble showed a very different pattern, with an increase in the accumulated annual abundance from 1600 in Spain, peaking at 41,000 in northern Germany and then decreasing again toward northern latitudes. For the two species ensembles and C. imicola, the season began between January and April, with later start dates and increasingly shorter vector seasons at more northerly latitudes.

CONCLUSION

We present the first maps of seasonal Culicoides abundance in large parts of Europe covering a gradient from southern Spain to northern Scandinavia. The identified temporal trends and spatial patterns are useful for planning the allocation of resources for international prevention and surveillance programmes in the European Union.

Lumpy skin disease: I. Data collection and analysis

An epidemiological analysis of the temporal and spatial patterns of LSD epidemics and of the risk factors for LSD spread in south‐eastern Europe was performed, based on the data collected from affected and at risk countries. Since 2015, the extent of the LSD epidemics in south‐eastern Europe was over 7,600 LSD outbreaks with 12,800 affected animals, with most outbreaks occurring between May and August. Most LSD spread occurs over a relatively small distance, approximately between 10 and 20 km, and the speed of propagation was estimated to be mostly up 2 km/day, in agreement with the vector‐borne pattern of LSD. Proximity to affected farms, warm temperatures and related vector abundance were among the main risk factors for LSD spread. Within a few months’ at least 90% of the animal population had been vaccinated with live homologous vaccine against LSD in south‐eastern Europe. Where almost total vaccination coverage was achieved, no further outbreaks were reported. The vaccination effectiveness in Albania was estimated to be around 70% at farm level and 77% at animal level. Possible adverse effects to live homologous vaccine, including fever, decreased milk production and oedema at injection site were reported in Croatia (a LSD‐free country) mostly within 2 weeks after vaccination, in 0.09% of the vaccinated animals. Unique farm identifiers should be always used across all databases, so to allow further analysis especially on improving the mathematical models for more robust estimates of transmission parameters applicable to the region, and for better estimation of vaccination effectiveness. All suspected clinical cases in vaccinated animals should be confirmed by differentiating field virus from vaccine strain. Trapping surveys for estimation of vector abundance can be carried out by targeting some sentinel farms, to be followed up during the whole LSD season, while long‐term studies can give more accurate information about species composition and seasonality of potential LSD vectors.