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Given that bovine herpesvirus 1 (BoHV-1) -the causative agent of Infectious Bovine Rhinotracheitis (IBR)- is still endemic in most European countries, BoHV-1 free herds are subject to a considerable risk of (re)introduction of the virus. The aim of this literature review was to describe published, quantified risk factors that are relevant for the introduction of BoHV-1. The risk factors described in this study can be used as input for modeling eradication scenarios and for communication on biosecurity measures to stakeholders. A literature search was conducted in November 2020 in two major online search databases, PubMed and Web of Science. The search criteria “risk factor” combined with different synonyms for BoHV-1 were explored, which resulted in 564 hits. Only studies performed in Europe, written in Dutch, English, French, German or Spanish with an English summary and that quantified risk factors for introduction of BoHV-1 into cattle herds were included. Studies had to quantify the risk factors with crude odds ratios (OR), an estimate of the chance of a particular event occurring in an exposed group to a non-exposed group. After checking for duplicates and excluding articles that did not meet the inclusion criteria, 12 publications remained for this review. Risk factors were classified into seven groups, i.e., herd characteristics, management, animal characteristics, purchase, direct animal contact, neighborhood and indirect transmission routes. Most relevant factors for introduction of BoHV-1 into cattle herds include herd size, purchase of cattle, cattle density, age of cattle, distance to neighboring cattle herds and professional visitors. Together with other direct and indirect animal contacts, these factors are important when elimination of BoHV-1 is considered. A closed farming system and protective clothing for professional visitors can eliminate the major routes of introduction of BoHV-1 in cattle herds. To the best of our knowledge, this is the first systematic review solely focussing on measures that can be taken to control introduction of BoHV-1 into cattle herds. Besides testing, focus on managing these (biosecurity) factors will decrease the risk of introducing the virus.

Bovine viral diarrhea (BVD) is controlled in many countries by detection and culling of persistently infected (PI) animals. The most important risk factor for BVDV introduction is purchase. An introduced cow can be PI and transmit the virus to other cattle in the herd. If she is not PI but is pregnant, there is still a risk because the subsequently born calf may be PI, when she encountered the virus in early pregnancy. To control this risk, all cows > 1 year from non-BVDV-free herds that are introduced in herds that participate in the Dutch BVDV control program are tested for virus and antibodies. Depending on the results, subsequent measures such as suspension of the BVDV-free status, removing the animals from the herd, or testing the off-spring of the cow for virus, are undertaken. The aim of this study was to evaluate the results of this risk mitigating measure. Data on cattle movements, calving's, herd-level BVDV status, and animal-level test data were available from all dairy herds that participated in the national BVDV control program (>14,000 dairy herds) for the year 2019. The data were combined and parameters of interest were calculated, i.e., (i) the number of purchased BVD virus positive cattle and (ii) the number of BVD virus positive calves born from purchased cows within 9 months after introduction. In 2019, 217,301 cattle were introduced in Dutch dairy herds that participated in the BVDV control program. Of these, 49,820 were tested for presence of BVD virus and 27 (0.05%) cows introduced in 21 different herds tested BVD virus positive. Out of 46,727 cattle that were tested for antibodies, 20.5% tested positive. The seropositive cows produced 4,341 viable calves, of which 3,062 were tested for virus and subsequently, 40 (1.3%) were found BVD virus positive. These 40 BVD virus positive calves were born in 23 herds. The risk mitigating measure led to detection of 67 BVD virus positive animals in 44 unique herds in 2019. This study makes plausible that the probability and impact of re-introduction of BVDV can be minimized by testing introduced cattle and their subsequently born calves.

Dairy cows are negatively affected by the introduction of bovine viral diarrhea virus (BVDV), and consequently, produce less milk. Existing literature on potential milk production losses is based on relatively outdated data and hardly evaluates milk production loss in relation to a new BVDV infection in a surveillance system. This study determined the annual and quarterly loss in milk production of BVDV introduction in 3,126 dairy herds participating in the Dutch BVDV-free program between 2007 and 2017. Among these herds, 640 were "breakdown-herds" that obtained and subsequently lost their BVDV-free status during the study period, and 2,486 herds obtained and retained their BVDV-free status during the study period. Milk yields before and after BVDV introduction were compared through annual and quarterly linear mixed models. The fixed variables for both models included herd type (breakdown-herd or free-herd), bovine viral diarrhea status (on an annual and quarterly basis), year, season, and a random herd effect. The dependent variable was the average daily milk yield on the test day. To define the possible BVDV-introduction dates, 4 scenarios were developed. In the default scenario, the date of breakdown (i.e., loss of the BVDV-free status) was assumed as the BVDV-introduction date. For the other 3 scenarios, the BVDV-introduction dates were set at 4, 6, and 9 mo before the date of breakdown, based on the estimated birth date of a persistently infected calf. In the default scenario, the loss in milk yield due to BVDV introduction occurred mainly in the first year after breakdown, with a reduction in yield of 0.08 kg/cow per day compared with the last year before breakdown. For the other 3 scenarios, the greatest yield reduction occurred in the second year after BVDV introduction, with a loss of 0.09, 0.09, and 0.1 kg/cow per day, respectively. For the first 4 quarters after BVDV introduction in the default scenario, milk yield loss was 0.14, 0.09, 0.02, and 0.08 kg/cow per day, respectively. These quarterly results indicated that milk yield loss was greatest in the first quarter after BVDV introduction. Overall, BVDV introduction had a negative, but on average a relatively small, effect on milk yield for herds participating in the BVDV-free program. This study will enable dairy farmers and policymakers to have a clearer understanding of the quantitative milk production effect of BVDV on dairy farms in a control program.

The outcomes of a voluntary bovine viral diarrhoea virus (BVDV) control programme that has been in place in the Netherlands since 1997 were analysed. This ‘BVDV-free’ programme was studied in dairy herds in the period 1 August 2007 to 1 August 2013. The programme was based on a test and cull approach at the herd level, after which the BVDV status was monitored by testing young stock for antibodies against BVDV or by antigen testing of newborn calves. One of the challenges of the programme was that, without any legislation or subsidies, farmers had to be motivated to pay all costs involved, with eradication of BVDV from their farm as the only incentive. During the study period, the percentage of dairy farms with a ‘BVDV-free’ status in the Netherlands increased from 13% to 24%, while the prevalence of active BVDV infections in Dutch dairy herds decreased. This may be related to the increasing number of participants in the ‘BVDV-free’ programme.

The existence, stage of eradication and design of control programmes (CPs) for diseases that are not regulated by the EU differ between Member States. When freedom from infection is reached (or being pursued), safe trade is essential to protect (or reach) that status. The aim of STOC free, a collaborative project between six countries, is to develop and validate a framework that enables a transparent and standardized comparison of confidence of freedom for CPs across herds, regions or countries. The framework consists of a model combined with a tool to facilitate the collection of the necessary parameters. All relevant actions taken in a CP are included in a Bayesian network model, which allows prior distributions for most parameters. In addition, frequency of occurrence and risk estimates for factors that influence either the probability of introduction or temporary misclassification leading to delayed detection of the infection are included in the model. Bovine viral diarrhoea virus (BVDV) is used as an example disease. Many countries have CPs in place for BVDV and although elements of the CPs are similar, biosecurity measures and testing protocols, including types of tests and testing frequency, as well as target groups, differ widely. Although the initially developed framework is based on BVDV, the aim is to make it sufficiently generic to be adaptable to CPs for other diseases and possibly other species. Thus, STOC free will result in a single general framework, adaptable to multiple disease CPs, which aims to enhance the safety of trade. European Food Safety Authority

International audience; Countries differ in existence, stage of eradication and design of control programs for non-regulated diseases. When freedom from infection is achieved, safe trade is essential to protect that status. The aim of STOC free, a collaboration between six countries, is to develop and validate a framework that enables transparent and standardized comparison of confidence of disease freedom for control programs across herds, regions or countries. The framework consists of a model (STOC free MODEL) combined with a tool to facilitate the collection of the necessary parameters (STOC free DATA). All actions taken in a control program will be included in a Bayesian model, which needs prior distributions for most parameters. Data for the distributions can be obtained from databases of control programs, demographic data and contact structures between herds. In addition, frequency of occurrence and risk estimates for factors that influence either the probability of introduction or delayed detection of the infection will be included in the model. Bovine viral diarrhea virus (BVDV) is used as an example disease. Many countries have control programs in place for this complex and detrimental disease with wide differences between application of vaccinations, combinations of diagnostic tests applied, frequency of testing and target groups. Although BVDV will be a thorough test of the initial developed framework, it should be generic enough to be adaptable to control programs for other diseases. With the introduction of the new Animal Health Law (AHL), it is anticipated that assessments of the performance of control programmes will progressively change towards output-based measures. The STOC free framework will support the AHL by providing a single general framework, adaptable to multiple diseases, which aims to enhance the safety of trade.

International audience; Objective: Several European countries have implemented control or eradication programmes for non-regulated diseases such as bovine viral diarrhoea virus (BVDV). However, the diversity in such control programmes (CP) creates difficulties for intra-community trade given that the probability of freedom from e.g. BVDV will differ between countries. This poses a risk of potential movement of BVDV into free regions. An understanding of equivalence with respect to disease freedom is important when seeking to facilitate interstate animal movements,whilst also managing the risk of infection. In this project, six European countries collaborate to develop an output-based approach to assess and compare confidence of freedom resulting from different CPs. The aim was to qualitatively compare the confidence of freedom resulting from different BVDV CPs. Materials and methods: An existing tool for harmonized description of surveillance programmes (the RISKSUR tool) was used to collect information from each participating country about BVDV status, demographic information and surveillance activities for BVDV, and expanded to also include control measures of the BVDV CPs. Results: The design of BVDV CPs differed considerably as well as country demographics (Table 1). The aspects of the different CPs were grouped in three main topics: context (i.e. BVDV status, occurrence of risk factors), actions to obtain a BVDV free status and measures to monitor the free status. Conclusions: The variation in context was larger than the variation in control programmes, resulting in different risk classifications for territories. The context of a country or territory is crucial information for an outcomebased comparison of BVDV CPs.

International audience

International audience