Bovine viral diarrhea (BVD) eradication in Switzerland--experiences of the first two years

A national eradication programme was designed with the aim of achieving total freedom from bovine viral diarrhea virus (BVDV) infection in the Swiss cattle population. The eradication programme consisted of testing every Swiss bovine for antigen, culling virus-positive animals and applying movement restrictions. Starting in 2008, the campaign achieved the goal of reducing the proportion of newborn calves that were virus-positive from 1.8% to under 0.2% within two years (situation in September 2010). Both good data flow between the parties involved as well as speed and efficiency (e.g. concerning the application of tests, movement restrictions and slaughter) are central to the success of the programme. Since the beginning of the programme 2.85 million cattle have been tested for bovine viral diarrhea virus (BVDV). The BVD-prevalence in cattle at the individual and herd levels following the implementation of the eradication programme was assessed. Using data collected during this campaign a risk factor analysis was conducted in order to identify factors associated with the appearance of virus positive newborn calves in herds where BVD had not previously been detected; these risk factors would allow targeting of future surveillance. Herd size, early death rate (i.e. the number of animals that either die before 15 days of age or are stillborn per number of newborns per year), buying in stock, using communal summer grazing, production type, age structure and management strategy were factors associated with the appearance of new cases of infection. Testing of newborn calves for antigen will continue to be conducted until the end of 2011, this is combined with outbreak investigation of newly infected herds (consisting of re-testing dams of virus-positive calves and if necessary all cattle on or that recently left the farm). This process is done to identify infected animals that may have been missed during prior testing (false negatives), it also serves to identify other factors that may be responsible for the introduction of BVDV onto the farm. Since October 2009, testing of calves for antigen combined with outbreak investigation has led to the detection of 55 infected animals that had tested negative (presumably false negative) during previous rounds of testing.     

Bovine virus diarrhoea (BVD) control programme in an area in the Rome province (Italy)

A BVD control programme based on the identification and removal of persistently infected (PI) animals is being undertaken in an area in the Rome province, where BVD outbreaks had been previously detected. It involves 174 mainly dairy herds, from which blood samples of all bovines older than 1 year are obtained through the national brucellosis and leukosis eradication programme. Samples sufficient to detect the presence of seropositive animals at a prevalence of 5% or more are initially screened for antibodies against BVD virus (BVDV) using an immunoenzymatic assay. Upon identification of seroreagents additional blood samples are tested from the 6-12-month age category not included in the initial samples. Animals are considered immunotolerant if BVDV is demonstrated twice at a minimum 30-day interval. When no seropositive animals are detected during the first serological screening the herd is declared BVD-free if a second testing, preferably carried on the same animals previously tested, confirms the seronegative status of the herd. At present 147 farms have been tested, of which 63 (42.9%) are negative with respect to antibodies against BVDV. Of the 84 remaining herds in which one or more seropositives are detected, 13 are classified as recently infected. In eight of these recently infected herds, 22 PI animals have been identified.     

Evaluation of producer and consumer benefits resulting from eradication of bovine viral diarrhoea (BVD) in Scotland, United Kingdom

In this paper we evaluated the distributional effects on actors in the milk market of a hypothetical programme to eradicate bovine viral diarrhoea (BVD) from the Scottish dairy herd. With this in mind, we applied an economic welfare methodology which utilizes data on price, on output quantity, on elasticities of supply and demand and on simulated cost and yield effects of an eradication programme. Our analysis is based on Markov-chain Monte Carlo simulation of BVD spread in the dairy herd. We found that consequent upon the eradication of the disease milk yield per cow increased for all herd sizes in Scotland whereas milk price received by farmers fell. Consequently, milk consumers gained around pound11 million in discounted economic surplus and producers with infected herds gained around pound39 million whereas producers with un-infected herds lost around pound2 million in discounted surplus. On balance, however, the eradication programme generated around pound 47 million in discounted economic gain for Scotland. We found that the results are sensitive to changes in yield gains made by owners of the infected herd.     

Implementation of two-step vaccination in the control of bovine viral diarrhoea (BVD)

Bovine viral diarrhoea (BVD) control/eradication programmes based on the test and removal of persistently infected cattle without use of vaccination were first introduced by the Scandinavian countries in the early 1990s. Within the last 10 years the programmes have proven to be very successful and have served as a blueprint for several other European regions. However, in areas with high cattle densities, intense animal trade and high BVD prevalence this control approach is risky, because there is a high probability that herds, which have been cleared of persistently infected (PI) animals and have become partly or fully susceptible to reintroduction of the virus, will come in contact with a BVD virus (BVDV) infected animal. A combination of the test and removal strategy with subsequent systematic vaccination of cattle could overcome this problem. The goals of vaccination in such a programme is protection against reintroduction of BVDV into herds free from PI cattle and foetal protection of pregnant animals accidentally exposed to the virus. Two-step vaccination is based on the use of inactivated BVDV-1 vaccine for priming followed by a live attenuated vaccine booster 4 weeks later. The immune response elicited by such a vaccination scheme has proven to be long lasting and foetal infection after challenge with BVDV-1 and BVDV-2 was prevented in pregnant animals 5 months after vaccination. These findings suggest that the implementation of a two-step vaccination in the initial phase of control programmes in addition to test and removal of PI animals in areas with high cattle densities and endemic BVD is practical and efficacious.     

Prevalence and geographic distribution of bovine viral diarrhoea (BVD) infection in Finland 1993-1997

Bulk milk samples from every herd supplying milk to dairies in Finland were examined for the presence of antibodies to BVD virus (BVDV) annually during 1993-1997. The highest prevalence, 0.99% in 1994, declined to 0.37% in 1996; however, this favourable trend appeared to discontinue in 1997, where the prevalence remained at 0.41%. In 1993, sera of all individual animals from bulk milk antibody-positive herds were examined for the presence of these antibodies. Since 1994, only sera of animals from herds with a bulk milk absorbance reading greater than 0.250 in the EIA test were examined individually. Three geographic foci of BVDV antibody-positive dairy herds were resolved in 1994, one in the north-western, another in the eastern and a diffuse third in the southern part of Finland. A distinct limiting of the spread was apparent in 1997. Beef cattle were also studied during 1993-1997; in 1993 breeding units, in 1994 mainly beef suckler herds and in 1995-1997 serum samples of beef animals at slaughter were examined for the presence of antibodies to BVDV. The prevalence of seropositive herds in 1993 and 1994 was 30.2% and 3.2%, respectively, while the prevalence among slaughter animals ranged 0.8-1.6%. Seronegative animals in herds with > 50% of seropositive animals were examined for the presence of BVD-virus. A total of 40 dairy herds and two beef herds with viraemic (persistently infected, PI) animals was encountered during 1993-1997. A comprehensive control programme and a more specific, cooperatively funded eradication programme for dairy cattle were launched in 1994. These programmes most probably contributed to the decline in prevalence during 1994-1996.     

Experiences from the Danish programme for eradication of bovine virus diarrhoea (BVD) 1994-1998 with special reference to legislation and causes of infection

The main experiences from the Danish bovine virus diarrhoea (BVD) eradication programme over 5 years from 1994 to 1999 are presented. The last 3 years of the programme has been strongly supported by legislation. The most important regulations have been blood testing of live animals before movement to other herds, common pastures or exhibitions, and monitoring of all herds at regular intervals for the presence of the infection. Nevertheless, free herds have experienced infection, e.g., 204 dairy herds in 1998. Of herds found to be infected in the period from July 1997 through June 1998 after previously having been registered to be BVD-free, 67 herds were thoroughly investigated. Nineteen herds (28%) were found infected because of purchase of pregnant cows or heifers which delivered persistently infected (PI) calves, and 24 (36%) and two (3%) because of PI animals on neighbouring pastures or in neighbouring farm houses, respectively. In five herds (7%) pregnant heifers had become infected on one and the same common pasture, while in 17 herds (25%) no immediate cause of infection could be demonstrated. Yet, airborne spread from PI herds as a source of infection was suspected in some of these cases. It was furthermore concluded from investigations presented, that antibody-positive AI bulls were a remote but unlikely possibility. Free-living deer in Denmark had to be considered uninfected. Presence of PI-animals in sheep on infected farms has been seen and is paid attention to in individual cases. The results underline the need for legislation to be used in eradication programmes in areas with a high prevalence of infection and to be introduced right from the beginning in order to minimise the risk of infection for free herds.     

Bovine viral diarrhoea virus in beef cattle herds of Yucatan, Mexico: seroprevalence and risk factors

A survey of bovine viral diarrhoea virus (BVDV) infection was carried out from June 2001 to July 2002 in a non-vaccinated beef cattle population from the livestock region of Yucatan, Mexico, to assess seroprevalence and identify risk factors related to seroprevalence. The aim was also to estimate the intra-herd correlation (r_e) and design effect (D) of BVDV seropositivity. Cattle were selected by a two-stage cluster sampling. Blood samples were collected from 560 animals originating from 40 herds. Sera were tested for antibodies against BVDV using an indirect ELISA test. The sensitivity and specificity of the test was 97.9 and 99.7%, respectively. Risk factors regarding the herd and each animal sampled were recorded through a personal interview at the time of blood sampling. Twenty-four of the 40 herds had at least one seropositive animal. The animal true seroprevalence was estimated as 14%. The marginal logistic regression model used to describe the data found a significant (p < 0.05) association of herd size–cow-origin interaction. The interaction was due to a higher risk of seropositivity in the category of herds with ≤100 animals and purchased cows (OR = 1) as compared to herds with ≤100 animals and cows born in the farm (OR = 0.23). Seropositivity between cows purchased and cows born in the farm was similar for herd sizes of 101–196 and >196 animals. The r_e and D values were 0.17 ± 0.05 and 3.16 ± 0.57, respectively.     

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.     

Bovine viral diarrhoea virus (BVDV) diversity and vaccination. A review

BVDV is associated with a range of economically important clinical diseases including reproductive disorders and acute fatal haemorrhagic disease in cattle industry. Vaccination is still the most important control strategy for controlling BVDV infections in many countries of the world. The existence of great genetic and antigenic diversity of BVDV isolates is very important concern for BVDV vaccine development and protective efficacy of current vaccines. In this review, the protective efficacies of the selected examples of BVDV vaccines with regard to BVDV diversity and the novel marker vaccine development studies are discussed.     

Bovine viral diarrhoea: Pathogenesis and diagnosis

Bovine viral diarrhoea virus (BVDV) is the most prevalent infectious disease of cattle. It causes financial losses from a variety of clinical manifestations and is the subject of a number of mitigation and eradication schemes around the world. The pathogenesis of BVDV infection is complex, with infection pre- and post-gestation leading to different outcomes. Infection of the dam during gestation results in fetal infection, which may lead to embryonic death, teratogenic effects or the birth of persistently infected (PI) calves. PI animals shed BVDV in their excretions and secretions throughout life and are the primary route of transmission of the virus. These animals can usually be readily detected by virus or viral antigen detection assays (RT-PCR, ELISA), except in the immediate post-natal period where colostral antibodies may mask virus presence. PI calves in utero (the ‘Trojan cow’ scenario) currently defy detection with available diagnostic tests, although dams carrying PI calves have been shown to have higher antibody levels than seropositive cows carrying non-PI calves.Acute infection with BVDV results in transient viraemia prior to seroconversion and can lead to reproductive dysfunction and immunosuppression leading to an increased incidence of secondary disease. Antibody assays readily detect virus exposure at the individual level and can also be used in pooled samples (serum and milk) to determine herd exposure or immunity. Diagnostic tests can be used to diagnose clinical cases, establish disease prevalence in groups and detect apparently normal but persistently infected animals. This review outlines the pathogenesis and pathology of BVD viral infection and uses this knowledge to select the best diagnostic tests for clinical diagnosis, monitoring, control and eradication efforts. Test methods, types of samples and problems areas of BVDV diagnosis are discussed.     

Control and eradication programme of enzootic bovine leucosis (EBL) from selected dairy herds in Turkey

Serum samples of 15,909 cattle from 31 dairy herds located in various regions of Turkey were tested for the presence of antibodies against bovine leucosis virus (BLV) using Agar Gel Immuno-diffusion technique (AGID). 48.3% (15/31) of the herds had seropositive animals and positivity rates were detected from 0.5-34.4% in these herds. In an EBL control/eradication programme all seropositive animals were culled in the infected herds. Thereafter, a total of 74,347 sera were tested for the presence of BLV specific antibodies. The serological results and detail of EBL control/eradication programme were shown in this paper.     

Severe malformations in calves associated with bovine viral diarrhoea (BVD) virus infection in a dairy cattle herd

During late may 2004, Some dairy cows at Al-Kharj area of central Saudi Arabia, gave birth to severely malformed calves which died, few hours to few days following birth. Samples were collected from the affected calves and their dams of virological and serological investigations. Bovine viral diarrhoea virus was detected by capture enzyme linked immuno-sorbent assay (ELISA) in the brains of affected calves. Serum antibodies were detected in the dams. The present study indicated that in spite of vaccination against BVD in the country, still severe affections of the disease are encountered. Further insight epidemiological studies to elucidate the BVD situation in Saudi Arabia is urgently needed.