The Schmallenberg virus epidemic in Europe—2011–2013

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Abstract

During the Schmallenberg virus (SBV) epidemic, the European Food Safety Authority (EFSA) collected data on SBV occurrence across Europe in order to provide an assessment of spread and impact. By May 2013, twenty-nine countries were reporting to EFSA and twenty-two countries had reported cases of SBV. The total number of SBV herds reported was 13,846 and the number of SBV laboratory confirmed herds was 8730. The surveillance activities were based on the detection of SBV clinical cases (either adults or newborns). Malformation in newborns was the most commonly reported clinical sign of SBV-infection. All countries were able to provide the date when the first suspicion of SBV in the herd was reported and nineteen could report the location of the herd at a regional level. This allowed the spread of SBV in Europe to be measured both temporally and spatially. The number of SBV confirmed herds started to increase in December 2011 and two peaks were observed in 2012 (February and May). Confirmed herds continued to be reported in 2012 and into 2013. An increase during winter 2012 and spring 2013 was again observed, but the number of confirmed herds was lower than in the previous year. SBV spread rapidly throughout Europe from the initial area of detection. SBV was detected above the latitude of 60° North, which exceeds the northern expansion observed during the bluetongue virus serotype 8 epidemic in 2006–2009. The impact of SBV was calculated as ratio of the number of herds with at least one malformed SBV positive foetus and the total number of herds in this region. The 75th percentile of the malformations ratio in the various affected countries for the whole reporting period was below 1% and 3% for cattle and sheep herds, respectively. International data collection on emerging diseases represents a challenge as the nature of available data, data quality and the proportion of reported cases may vary widely between affected countries. Surveillance activities on emerging animal diseases are often structured only for case detection making the estimation of infection/diseases prevalence and the investigation of risk factors difficult. The impact of the disease must be determined to allow risk managers to take appropriate decisions. Simple within-herd impact indicators suitable for emerging disease outbreaks should be defined that could be measured as part of routine animal health surveillance programmes and allow for rapid and reliable impact assessment of emerging animal health diseases.

Introduction

The ongoing systematic collection and analysis of animal disease data is the core of an animal disease surveillance system. It should result in relevant intelligence at an appropriate spatial and temporal resolution to support risk managers in taking decisions to prevent and control animal diseases and possible public health implications. Important requirements for existing surveillance systems to ensure preparedness for emerging diseases at European level are: clear and specific case definitions, integration with laboratory services and use of appropriate and validated diagnostic reagents and methods, consistent and robust epidemiological indicators and generic data models to facilitate data transfer and analysis (Richardson et al., 2011). In recent years, the need to perform risk assessments at a European Union (EU) level for animal diseases required the development of ad-hoc data collections on emerging and re-emerging diseases like bluetongue serotype 8 (EFSA, 2007) and Q fever (EFSA, 2010). Such ad-hoc data collections were necessary to estimate disease prevalence, spread or impact.

In August 2011, farmers and veterinarians in North Rhine-Westphalia (Germany), the Netherlands and Belgium started to report cases of clinical disease in cattle (Hoffmann et al., 2012, Muskens et al., 2012, Cay et al., 2011). Clinical signs were unspecific and transitory: fever, drop of milk yield for several days and in some cases also diarrhoea. Several disease agents such as bluetongue virus, bovine viral diarrhoea virus, bovine herpes virus-1, malignant catarrhal fever virus foot-and-mouth disease virus and exotic viruses like epizootic hemorrhagic diseases virus, Rift Valley fever virus or bovine ephemeral fever virus were excluded by diagnostic analysis. In November 2011, the German national reference laboratory (FLI) detected genomic sequences of a new Orthobunyavirus; the virus was provisionally named “Schmallenberg virus” (SBV) (Hoffmann et al., 2012). Subsequently, the same virus was detected in samples from malformed lambs and calves in Germany, Belgium and the Netherlands (ProMEd-mail, 2011a, ProMEd-mail, 2011b, Van den Brom et al., 2012).

The disease situation was presented by these three countries at the Standing Committee on the Food Chain and Animal Health (SCoFCAH), the EU member states (MS) representation on matters related to Animal Health, in January 2012. The MS and the European Commission (EC) issued a statement on the disease, recognising the need to collect and share information (EC, 2012).

In the EU, the Animal Disease Notification System (ADNS) application is used to ensure rapid exchange of information between MS and the EC on outbreaks of notifiable diseases. The diseases which are classified by the EU as notifiable are listed in EU legislation (Annex I to Directive 82/894/EEC). Notification implies not just reporting but also the need for control or eradication measures to be put in place. However, the system does not include provisions for collection of information on emerging diseases and an ad hoc data collection was necessary. The European Food Safety Authority (EFSA) was requested by the EC to collect data on SBV occurrence from MS in order to provide an assessment on SBV spread and impact.

The EU and each of its MS are members of the World Organization for Animal Health (OIE) and therefore have the obligation to report animal diseases detected in their territory. The large majority of disease reports are on listed diseases. The inclusion of an animal disease to the OIE list follows a detailed procedure: a recommendation by the OIE relevant ad hoc group is submitted for endorsement by the relevant elected specialist commissions before it is presented for final adoption by the World assembly of delegates. The criteria for the inclusion of a disease in the OIE List are described in detail in the OIE code. In brief, they relate to feasibility of diagnosis, characteristics of the disease spread and its impact either on public health, animal health or the environment. Diseases can also be listed as emerging diseases when there is evidence of zoonotic potential, rapid spread or significant morbidity and mortality. An “emerging disease” is – as defined by the OIE – a new infection resulting from the evolution or change of an existing pathogenic agent, a known infection spreading to a new geographical area or population, or a previously unrecognized pathogenic agent or disease diagnosed for the first time and which has a significant impact on animal or public health (OIE, 2013).

Listing by the OIE as well as inclusion on the list of notifiable diseases by the EU legislation makes it necessary to establish surveillance measures that allow demonstration of disease freedom, early detection and control measures to avoid the spread or the introduction of the disease. The economic impact of such measures can be high and risk managers need to decide on their value. The OIE was notified of the first and of subsequent cases of SBV detected in various MS of the EU as an emerging disease. However, to make SBV infection a listed disease in accordance with the OIE, demonstrating the spread and impact of the infection is required.

The objectives of this study were to describe the European data collection effort regarding the SBV epidemic, present the results of the disease spatial and geographic distribution during 2011–2013 and discuss its possible impact. In addition, the level of under-ascertainment of the surveillance system was assessed in order to improve the accuracy of our estimates.

Section snippets

Data collection: reporting officers network nomination and organization, data reporting guidelines

The notification of SBV in the EU was not compulsory. Neither mechanism nor guidelines were available for a harmonised data collection and reporting of a non-notifiable disease.

Harmonised case definitions were agreed between the MS. The information related to suspect and confirmed herds was collected at national level by National Veterinary Competent authorities and reported to EFSA by officially appointed reporting officers. The systems in place for dissemination of information on the case

Surveillance activities

Surveillance activities varied considerably within Europe. An overview of the surveillance activities in the reporting countries is presented in Table 2. The network of reporting organisations comprised a mix of veterinary organisations, agricultural ministries, research institutes, national animal health institutes, farmers’ organizations and food safety agencies depending on the existing structures within the countries. By May 2013, the network included twenty-six MS, two countries in the

Discussion

The objective of EFSA's coordinated SBV data collection at a European level was to investigate the spread of the disease and assess its impact in order to support EU risk managers to take decisions on the implementation of control measures and to provide information to trade partners.

At the start of the epidemic, surveillance activities were based on case reporting of clinical suspicions to the competent authorities. This type of surveillance is considered passive because the decision to report

Conclusions

The work developed by EFSA and experts of the member states of the European Union on the development of uniform case definitions and protocols for data submission demonstrated the possibilities of international collaboration in the investigation of an emerging disease. The collated data allowed for the assessment of the spread of SBV in Europe both temporally and spatially at an appropriate granularity to support decision makers.

Information on the results of the laboratory testing could be

Conflict of interest

None declared.

Acknowledgments

The authors would like to acknowledge all reporting officers that have submitted data on SBV occurrence in European countries, the EFSA Animal Health and Welfare Network on the Ad-hoc working group on Schmallenberg virus experts and EFSA scientific staff.

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