Prevalence of bovine virus diarrhoea virus infection in Belgian white blue cattle in southern Belgium

An Epidemiological and Economic Simulation Model to Evaluate Strategies for the Control of Bovine Virus Diarrhea in Germany

Models can be used to plan, evaluate, and improve programs for animal disease control. In Germany, a nationwide compulsory program to eradicate Bovine viral diarrhea (BVD) is in force since January 2011. As it is associated with substantial expenditures, the program is currently under revision. To provide the basis for a science-based decision on the future course of BVD control in Germany, we evaluated 13 scenarios (sc1-13) with respect to the chance of reaching freedom from disease and their economic implications for a period of 20 years (2011–2030). To simulate the impact of different control strategies on disease dynamics, a disease spread model was developed. To estimate the effects of a transient infection (TI) on animal level, a gross margin analysis was performed. To assess the value of cattle that died prematurely, a valuation model was used. Finally, an economic model was developed to perform a cost-benefit analysis and to compare each control scenario with a baseline setting with no BVD control. Costs comprised the expenditures for diagnostics, vaccination, preventive culling, and trade restrictions. Benefits were animal and production losses avoided by having control measures in place. The results show that reducing the PI prevalence on animal level to 0% is only feasible in scenarios that combine antigen or antibody testing with compulsory vaccination. All other scenarios, i.e., those based exclusively on a “test and cull” approach, including the current control program, will, according to the model, not achieve freedom of BVD by 2030. On the other hand, none of the scenarios that may lead to complete BVD eradication is economically attractive [benefit-cost ratio (BCR) between 0.64 and 0.94]. The average direct costs of BVD in Germany are estimated at 113 million Euros per year (34–402 million Euros), corresponding to 28.3 million Euros per million animals. Only the concepts of the former and the current national BVD control program (“ear tag testing and culling”) may reduce the BVD prevalence to 0.01% with an acceptable BCR (net present value of 222 and 238 million Euros, respectively, with a BCR of 1.22 and 1.24).

Assessment of listing and categorisation of animal diseases within the framework of the Animal Health Law (Regulation (EU) No 2016/429): bovine viral diarrhoea (BVD)

Bovine viral diarrhoea (BVD) has been assessed according to the criteria of the Animal Health Law (AHL), in particular criteria of Article 7 on disease profile and impacts, Article 5 on the eligibility of BVD to be listed, Article 9 for the categorisation of BVD according to disease prevention and control rules as in Annex IV and Article 8 on the list of animal species related to BVD. The assessment has been performed following a methodology composed of information collection and compilation, expert judgement on each criterion at individual and, if no consensus was reached before, also at collective level. The output is composed of the categorical answer, and for the questions where no consensus was reached, the different supporting views are reported. Details on the methodology used for this assessment are explained in a separate opinion. According to the assessment performed, BVD can be considered eligible to be listed for Union intervention as laid down in Article 5(3) of the AHL. The disease would comply with the criteria as in Sections 4 and 5 of Annex IV of the AHL, for the application of the disease prevention and control rules referred to in points (d) and (e) of Article 9(1). The assessment here performed on compliance with the criteria as in Section 3 of Annex IV referred to in point (c) of Article 9(1) is inconclusive. The animal species to be listed for BVD according to Article 8(3) criteria are mainly species of the families Bovidae, Cervidae and Camelidae as susceptible species and several mammalian species as reservoirs.

Survey for detecting persistently infected cattle with bovine viral diarrhea in Japan

To establish effective and efficient control measures for bovine viral diarrhea (BVD) in Japan, a pilot survey on persistently infected (PI) animals in dairy farms was conducted. A total of 5,949 cattle from 79 farms in 11 prefectures were tested; seven cattle in six farms were identified as PI animals. The proportion of farms with PI animals in Japan was calculated as 7.6% (95% confidence interval: 3.1–16.4%), and proportion of cattle tested as PI animals was 0.12% (95% confidence interval: 0.05–0.25%). The presence of only one or two animals in PI positive farms suggested the application of screening tests covering almost all cattle in each farm using pooled serum or bulk milk could be effective for implementing a large-scale survey for detecting PI animals.

Difficulties arising from the variety of testing schemes used for bovine viral diarrhoea virus (BVDV)

Globally, the eradication of bovine viral diarrhoea virus (BVDV) is still in its infancy, but eradication has been, or is being, adopted by several countries or regions. Comparisons between countries' schemes allow others to assess best practice, and aggregating published results from eradication schemes provides greater statistical power when analysing data. Aggregating data requires that results derived from different testing schemes be calibrated against one another. The authors aimed to evaluate whether relationships between published BVDV test results could be created and present the outcome of a systematic literature review following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. The results are tabulated, providing a summary of papers where there is potential cross-calibration and a summary of the obstacles preventing such data aggregation. Although differences in measuring BVDV present barriers to academic progress, they may also affect progress within individual eradication schemes. The authors examined the time taken to retest following an initial antibody BVDV test in the Scottish eradication scheme. The authors demonstrate that retesting occurred quicker if the initial not negative test was from blood rather than milk samples. Such differences in the response of farmers/veterinarians to tests may be of interest to the design of future schemes.

Economic risk analysis model for bovine viral diarrhea virus biosecurity in cow-calf herds

A stochastic model was designed to calculate the cost-effectiveness of biosecurity strategies for bovine viral diarrhea virus (BVDV) in cow-calf herds. Possible sources of BVDV introduction considered were imported animals, including the calves of pregnant imports, and fenceline contact with infected herds, including stocker cattle raised in adjacent pastures. Spread of BVDV through the herd was modeled with a stochastic SIR model. Financial consequences of BVDV, including lost income, treatment costs, and the cost of biosecurity strategies, were calculated for 10 years, based on the risks of a herd with a user-defined import profile. Results indicate that importing pregnant animals and stockers increased the financial risk of BVDV. Strategic testing in combination with vaccination most decreased the risk of high-cost outbreaks in most herds. The choice of a biosecurity strategy was specific to the risks of a particular herd.

Influence of category, herd size, grazing and management on epidemiology of bovine viral diarrhoea in dairy herds

The aim of this study was to estimate the influence of category, herd size, common grazing and management as risk factors in maintaining bovine viral diarrhoea infection in dairy herds. A total of 987 sera samples obtained from 202 heifers, 653 cows and 132 calves from 103 herds in Croatia were examined by enzyme-linked immunosorbent assay. In order to establish the prevalence of persistently infected cattle, 35 herds were selected. Ear notch tissue samples from all animals in selected herds (n = 2284) were collected and analyzed by antigen enzyme-linked immunosorbent assay. The true prevalence of specific antibodies was 61.61% and the estimated prevalence of exposure to bovine viral diarrhoea virus at the herd level was 100%. The prevalence of persistently infected animals was 0.53% and the prevalence of persistently infected herds was 20%. The antibodies prevalence was higher in cows, in herds that use common pasture and in larger herds (P < 0.001). The prevalence of persistently infected animals was not connected with the herd size but production management on big farms contributed to maintaining the virus. The obtained results suggest that production management was an important risk factor in bovine viral diarrohea epidemiology. High prevalence of antibodies and high prevalence of persistently infected herds requires implementation of control and eradication programs at a national or even regional level. The presented data complete the BVD epidemiological investigations from this part of Europe.

Prevalence of antibodies to bovine viral diarrhoea virus in bulk tank milk and associated risk factors in Scottish dairy herds

Bulk tank milk samples were collected from 374 dairy farms in Scotland in 2007/2008 along with questionnaire data relating to the management of the farm. Milk samples were tested for antibodies to bovine viral diarrhoea virus (BVDV) using a commercially available (Svanova) kit and percentage positivity scores calculated according to the manufacturer's guidelines. There were 220 farms that did not routinely vaccinate for bovine viral diarrhoea (BVD), and these were distributed according to the Swedish BVD eradication classes as 12.7 per cent, 22.3 per cent, 44.5 per cent and 20.5 per cent for Classes 0, 1, 2 and 3, respectively. A more sophisticated statistical method (finite mixture modelling) which does not depend on arbitrary thresholds and categories suggested a 73 per cent prevalence of herds with high mean levels of antibodies. Risk factor analysis suggested that routine vaccination for BVD, suspicion of BVD, housing of pregnant cows with calves, total number of cows and the proportion of cows that were dry were all associated with increased BVDV antibodies in bulk milk. The inclusion of BVD within the farm's health plan was associated with decreased BVDV antibodies in the bulk milk.

Serological and virological BVDV prevalence and risk factor analysis for herds to be BVDV seropositive in Belgian cattle herds

Bovine viral diarrhoea virus (BVDV) is a worldwide spread virus that most commonly infects cattle and can cause considerable economic losses. To determine the prevalence of BVDV in Belgium, a cross-sectional study was performed between November 2009 and March 2010. Young stock aged between 6 and 12 months from 773 randomly selected Belgian cattle herds were tested for BVDV-specific antibodies and antigen. With a target and maximum of 10 animals per sampled herd, a total of 5246 animals were selected. Additionally a questionnaire including different herd management topics and questions about participation in animal health programmes, including BVDV, was sent to 1100 Belgian cattle herds, including the 773 herds for BVDV testing. This paper focuses on results regarding these 773 herds. The true prevalence of BVDV-specific antibodies and antigen at herd level was respectively 47.4% and 4.4%, while at animal level this was respectively 32.9% and 0.3%. In 44.4% of the herds where BVDV-specific antibodies were detected at least 60% of the sampled young stock was BVDV seropositive. Interestingly, 83.4% of these farmers stated not to have suffered from problems related to BVDV. Moreover, only 8.4% of all farmers who completed the questionnaire (n=895) reported problems possibly related to BVDV the past 3 years. This demonstrates that farmers are often unaware of the presence of BVDV in their herd. Risk factors for a herd to be BVDV seropositive were identified by means of a multivariable logistic regression model. Large herds were significantly more likely to be BVDV seropositive (OR=1.004, p<0.01). The interaction between "Antigen positive animal detected in this study" and "BVDV vaccination in 2009" was significant (p<0.01). In non-vaccinating herds, the detection of antigen positive animals was significantly associated with BVDV seropositive herds (OR=13.8, p<0.01). In herds with no antigen positive animals detected, vaccination resulted in a significant risk factor to be BVDV seropositive compared to non-vaccinating herds (OR=3.4, p<0.01). Herds reporting BVDV-related problems the past 3 years were more likely to be BVDV seropositive (OR=1.9, p<0.05). This relation became non-significant (OR=1.8, p=0.08) when only a subset of herds with no vaccination of animals <12 months was taken into account. The results of the current study suggest an active circulation of BVDV in a considerable number of Belgian cattle herds.

Bovine viral diarrhoea virus seroprevalence and vaccination usage in dairy and beef herds in the Republic of Ireland

BACKGROUND

Bovine viral diarrhoea (BVD) is an infectious disease of cattle with a worldwide distribution. Herd-level prevalence varies among European Union (EU) member states, and prevalence information facilitates decision-making and monitoring of progress in control and eradication programmes. The primary objective of the present study was to address significant knowledge gaps regarding herd BVD seroprevalence (based on pooled sera) and control on Irish farms, including vaccine usage.

METHODS

Preliminary validation of an indirect BVD antibody ELISA test (Svanova, Biotech AB, Uppsala, Sweden) using pooled sera was a novel and important aspect of the present study. Serum pools were constructed from serum samples of known seropositivity and pools were analysed using the same test in laboratory replicates. The output from this indirect ELISA was expressed as a percentage positivity (PP) value. Results were used to guide selection of a proposed cut-off (PCO) PP. This indirect ELISA was applied to randomly constructed within-herd serum pools, in a cross-sectional study of a stratified random sample of 1,171 Irish dairy and beef cow herds in 2009, for which vaccination status was determined by telephone survey. The herd-level prevalence of BVD in Ireland (percentage positive herds) was estimated in non-vaccinating herds, where herds were classified positive when herd pool result exceeded PCO PP. Vaccinated herds were excluded because of the potential impact of vaccination on herd classification status. Comparison of herd-level classification was conducted in a subset of 111 non-vaccinating dairy herds using the same ELISA on bulk milk tank (BMT) samples. Associations between possible risk factors (herd size (quartiles)) and herd-level prevalence were determined using chi-squared analysis.

RESULTS

Receiver Operating Characteristics Analysis of replicate results in the preliminary validation study yielded an optimal cut-off PP (Proposed Cut-off percentage positivity - PCO PP) of 7.58%. This PCO PP gave a relative sensitivity (Se) and specificity (Sp) of 98.57% and 100% respectively, relative to the use of the ELISA on individual sera, and was chosen as the optimal cut-off since it resulted in maximization of the prevalence independent Youden's Index.The herd-level BVD prevalence in non-vaccinating herds was 98.7% (95% CI - 98.3-99.5%) in the cross-sectional study with no significant difference between dairy and beef herds (98.3% vs 98.8%, respectively, p = 0.595).An agreement of 95.4% was found on Kappa analysis of herd serological classification when bulk milk and serum pool results were compared in non-vaccinating herds. 19.2 percent of farmers used BVDV vaccine; 81% of vaccinated herds were dairy. A significant association was found between seroprevalence (quartiles) and herd size (quartiles) (p < 0.01), though no association was found between herd size (quartiles) and herd-level classification based on PCO (p = 0.548).

CONCLUSIONS

The results from this study indicate that the true herd-level seroprevalence to Bovine Virus Diarrhoea (BVD) virus in Ireland is approaching 100%. The results of the present study will assist with national policy development, particularly with respect to the national BVD eradication programme which commenced recently.

The prevalence of bovine viral diarrhoea virus infection in beef suckler herds in Scotland

Bovine viral diarrhoea (BVD) is an endemic disease of cattle that causes substantial losses to both beef and dairy production worldwide. The goal of this study was to estimate the prevalence of active BVD virus (BVDV) infection in beef suckler herds in Scotland. Information was collected from 301 herds using a stratified random sampling design based on agricultural census data. Herds were classified as with and without active infection based on the within-herd BVDV seroprevalence in young stock using Bayesian finite mixture modelling. This method accounted for within- and between-herd variability and allowed for classification error by the diagnostic tests. The observed sample data enabled the discrimination of three distinct seroprevalence cohorts. The results provided evidence of active BVDV infection in 16% of herds and no evidence of recent exposure in approximately two thirds of herds. The epidemiological significance of the further 16% of herds containing young stock with a median BVDV seroprevalence of 26.3-38.5% remains unclear. The fact that a large percentage of herds did not show evidence of recent infection is encouraging from an animal health and welfare perspective and the study provides a model for the further exploration of strategies aimed at BVD control at national level.

Detection of BVDV persistently infected animals in Belgium: Evaluation of the strategy implemented

Until now, no official bovine virus diarrhea virus (BVDV) control program has been implemented in Belgium. The only legislation dealing with the detection of BVDV-infected animals concerns the purchase of animals. A strategy of control, based on the identification and elimination of persistently infected (PI) animals and the vaccination of cows before insemination has been designed in both the Northern and the Southern part of the country. The strategy of detection of PI animals relies on PCR testing of pools of blood. Individual blood samples corresponding to the positive pools are then tested by BVDV-antigen ELISA. A first evaluation of the measures already applied in Belgium is presented. Data obtained in 2003 are presented and discussed regarding the validation of the laboratory strategy, the prevalence of positive herds, the genotype of circulating viruses, the outcome of antigen positive animals and the need for improvement of the current legislation.

Bovine viral diarrhoea virus infections and its control. A review

Infections with bovine viral diarrhoea virus continue to plague the cattle industry worldwide. The wish to control the negative effects of the virus has lead to the development of numerous vaccines, but also of eradication schemes. In this paper, a comprehensive overview on BVDV is given: the virus and its clinical manifestations, its occurrence and economic impact, the different routes of transmission, as well as diagnostic methods and objectives. Furthermore, the two major options for BVDV control--eradication and vaccination--are discussed as well as the risk for reintroduction of BVDV after eradication.

Serologic evaluation of five unvaccinated heifers to detect herds that have cattle persistently infected with bovine viral diarrhea virus

OBJECTIVE

To determine whether serologic evaluation of 5 unvaccinated 6- to 12-month-old heifers is a valid method for identifying herds that contain cattle persistently infected (PI) with bovine viral diarrhea virus (BVDV).

ANIMALS

14 dairy herds with a history of BVDV infection, with health problems consistent with BVDV infection, or at risk for contracting BVDV infection.

PROCEDURE

5 unvaccinated 6- to 12-month-old heifers were randomly selected from each herd. Neutralizing antibody titers for type-I and -II BVDV were determined. A herd was classified as likely to contain PI cattle when at least 3/5 heifers had antibody titers > or = 128. Virus isolation was performed on all cattle to identify PI cattle. Genotype of isolated viruses was determined by nested multiplex polymerase chain reaction.

RESULTS

6 of 14 herds contained PI cattle. Sensitivity and specificity of serologic evaluation of 5 heifers for identifying these herds were 66 and 100%, respectively. In herds that contained PI cattle, the predominant BVDV titer in the tested heifers corresponded to the genotype of the isolated virus.

CONCLUSIONS AND CLINICAL RELEVANCE

Serologic evaluation of unvaccinated 6- to 12- month-old heifers is an accurate method for identifying herds containing PI cattle. Both type-I and -II BVDV antibody titers should be determined to prevent herd misclassification. The genotype of BVDV found in PI cattle can be predicted by the predominant neutralizing antibody titers found in tested heifers. Serologic evaluation of 5 unvaccinated heifers can be used to determine whether a herd is likely to contain PI cattle.

Prevalence of cattle infected with bovine viral diarrhoea virus in Switzerland

A cross-sectional study was made in a major cattle-breeding area of Switzerland to investigate the prevalence and local distribution of animals antibody positive to bovine viral diarrhoea (BVD) virus and of persistently infected animals. The sample size and statistical analysis took into account the possible clustering of persistently infected animals on individual farms. Of 3440 animals tested on 121 farms, 1982 were found to have antibodies to BVD virus (95 per cent confidence interval for the population prevalence: 57.6+/-4.5 per cent) and 22 were persistently infected (estimate for the population prevalence: 0.64+/-0.34 per cent). The detection of persistent infection in animals less than seven months old was improved either by retesting one year later, by using an antigen-capture ELISA or, in selected cases, by the analysis of original serum samples by reverse-transcription PCR. The results showed that the prevalence of persistent infection may be underestimated by as much as one-third when antigen detection alone is used. None of the 121 farms investigated was free of antibody-positive animals and one in eight herds had at least one animal that was persistently infected. The prevalence of antibodies was lowest in seven- to 12-month-old animals (22.9 per cent) and highest in animals aged five years or over (84.9 per cent).