Project title: Benchmarking and control of Bovine Viral Diarrhoea Virus in Northern Ireland.
Duration: 24 months.
Background to proposal:
Bovine viral diarrhoea virus (BVDV) is an economically important pathogen in Northern Ireland dairy and beef herds. Losses may be associated with a wide range of reproductive effects, including conception failure and abortion, suppression of the immune system in calves, resulting in increased levels of pneumonia and diarrhoea, reduced milk yields, increased somatic cell counts and death of animals from mucosal disease, characterised by lameness, scour and oral ulceration.
In Great Britain, the estimated cost to the national herd in 1996 was calculated to be as high as £18M. More recent studies have suggested costs of £37/cow/year over a ten year period following introduction to a 100 cow beef herd, while costs in a 50 cow dairy herd have been estimated at £21/yr over ten years. While control of BVDV in Northern Ireland has remained non-systematic, largely relying on either a “do-nothing” approach or use of vaccine, this has not been the case elsewhere. A recent EU-funded Thematic Network has identified the need for a systematic approach to BVDV control that includes identification and removal of persistently infected (PI) animals. Increasingly other European countries are pursuing this type of systematic control and eradication scheme for BVDV. Norway, Sweden, Finland and Denmark are now essentially free, and Austria, Switzerland and Germany also have regional or national programmes in place. Within the UK, a successful eradication program, based on the Scandinavian model of control has been conducted on the Shetland Islands.
A bulk tank milk study conducted by Graham et al. in1999 found that >80 of NI dairy herds had evidence of current or recent infection with BVDV. Since that time several inactivated vaccines have been available for use, although typically this has been done without any systematic attempts to identify and remove the persistently infected (PI) animals that are the key means of introducing and spreading infection. The VSD laboratory has detected virus in over 1,300 diagnostic blood samples (consistent with the donor being a PI animal) in recent years. More recently, a study of aborted and stillborn bovine foetuses submitted to this laboratory for post mortem examination has found evidence of in utero exposure to BVDV in 17% of the 141 examined. In 2006, over 2,100 abortions were notified to DARD.
Although no formal control programs are yet in place in NI, the Agri-Food and Biosciences Institute (AFBI) has recently introduced voluntary cattle health schemes for the four most important endemic diseases of cattle: BVDV, infectious bovine rhinotracheitis virus (IBRV), leptospirosis and Johne’s disease. This scheme will allow herd owners to investigate their BVDV status, to pursue an eradication program where appropriate and to have BVDV-free herds accredited as such. The scheme will be run according to the rules of the Cattle Health Certification Standards (CHeCS). One of the key tools used in the scheme is screening of bulk tank milk samples, which gives an indication of previous exposure in milking cattle. Monitoring of dairy herds through sequential BTM sampling has been shown to be a useful tool in determining herd status and tracking changes in this, especially by identification of new infections. More recently, real time RT-PCR assays which can detect the presence of BVD virus (as opposed to antibodies) in BTM have also been developed and these have the potential to be a very cost-effective means of screening milking cows. This same technique can be used to detect virus in serum and skin samples (e.g. collected at ear tagging).
Within NI there is currently a lack of knowledge of:
- the progress made with BVDV control (and other endemic diseases) elsewhere in Europe,
- the tools available for BVDV control
- the current prevalence of BVDV in dairy herds,
- the incidence of new infections in dairy herds,
- the impact of vaccine usage and
- the applicability of newly developed real time RT-PCR techniques in control and eradication schemes.
This project will seek to address these shortcomings and knowledge gaps through delivery of the following objectives:
- Conduct BTM antibody survey of NI dairy herds for BVDV and IBRV to determine current status and changes in this status over time.
- Evaluate RT-PCR methods and use to determine the prevalence of herds with BVDV PI milking animals.
- •Evaluate and apply methods for screening young stock for BVDV e.g. ear notch testing for identification of persistently infected cattle.
- . Examine the impact of vaccination for BVDV on herd status.
- Determine strains of BVDV present in NI
- To arrange a local meeting for key stakeholders to communicate key facts and opportunities on BVDV control and eradication (including interim results from the project).
- To conduct BTM antibody surveillance of NI dairy herds for BVDV and IBRV to determine current status and changes in this status over time.
- To conduct BTM RT-PCR testing to determine the prevalence of dairy herds with persistently infected milking animals and to evaluate ear notch testing for identification of persistently infected cattle.
- To examine the impact of vaccination for BVDV on herd status.
- To examine risk factors associated with new infections in herds and investigate possible sources of these infections.
Collaborative research: (Will there be any work with other research institutes)
The expertise to conduct this work is available within VSD. Consequently there will be no formal involvement with other research institutes. However, the proposal will involve a significant amount of farm level testing and consequently will by necessity have a high level of collaboration with the industry.
Expanding on the objectives above:
Conduct BTM antibody survey of NI dairy herds for BVDV and IBRV to determine current status and changes in this status over time.
•Problem: no current knowledge of infection prevalence & incidence of breakdowns
–Use BTM samples collected at regular intervals
–Enrol population of herd owners in a regular surveillance program over 12-24 months
–Fill in questionnaire
–Categorize herds by status at the start of the study and monitor changes over time
–Results routinely reported back through their nominated veterinary surgeon
–Analyse results relative to questionnaire data
–Information to participating farmers (including freedom)
–Application of early intervention strategies or preventive measures in high-risk herds
–Generate prevalence data and incidence of breakdowns
–Risk factors associated with infection, breakdowns
Evaluate RT-PCR methods and use to determine the prevalence of herds with BVDV PI milking animals.
–current herd screening methods require individual sampling and testing. BTM RT-PCR has the potential to be a more rapid and cost effective alternative.
–Prevalence of herds with PI cows unknown
–Use BTM samples collected for Br testing
–Select method and conduct survey
–Individual investigation of selected positive farms
–Results routinely reported back through nominated vet
–Cost-effective method for herd owners to screen milking herd for PIs
–Knowledge of prevalence of herds with PI milking animals
–Feedback to herd owners and screening of herds on individual farms
Evaluate and apply improved methods for screening young stock for BVDV e.g. ear notch testing for identification of persistently infected cattle.
–For herd screening using conventional tests, young stock must be aged >4-6mo due to MDA. During their time in the herd they can cause extensive infection of other cattle, particularly other calves resulting in problems with scour and pneumonia. Improved techniques allowing screening shortly after birth are required.
–Select infected herd(s) (identified in Obj 1, 2)
–Evaluate methods for sampling and virus detection (e.g. ear notch testing, RT-PCR)
–Results routinely reported back through nominated vet
–Selection of suitable method for screening calves
–More rapid identification of PI animals
–More rapid clearance/accreditation of herds
–Benefits to individual participating herds
Examine the impact of vaccination for BVDV on herd status.
–Vaccines are now extensively used but minimal data on actual performance in the field, particularly when used in the absence of any other systematic controls
–Analysis of RT-PCR testing (milking cows, Obj 2) to compare numbers of herds with PI cows that are vaccinated compared to those that are not.
–Conduct spot testing of young stock in vaccinated and non-vaccinated herds
–Results routinely reported back through nominated vet
–Knowledge on vaccine use and performance
–Potential support for “vaccinated monitored free” accreditation route
–Information flow to participating herds
Determine strains of BVDV present in NI
–Two main strains- BVDV types I and II, with subtypes
–Vaccines typically BVDV Ia (not fully cross-protective with BVDV type II)
–BVDV II recently reported in GB, but it is not known if it is present in Northern Ireland
–Conduct strain typing of NI isolates
–Knowledge of strains present and possible impact on vaccine efficacy
Milestones with proposed dates: (commencement, end of project etc.)
- M1 DARD Approval of PhD studentship (M0)
- M2 Recruit study farms for monitoring (M0-6)
- M3 Selection of real time RT-PCR assay (M3-9)
- M4 Delivery of on-farm questionnaire and collation of responses (M6-12)
- M5 Conduct on farm BTM and blood antibody sampling (M6-30)
- M6 Conduct BTM RT-PCR sampling (M9-18)
- M7 Establish protocols and conduct studies to detect PI calves in first weeks of life (M12-24)
- M8 Conduct strain typing study (M24-32)
- M9 Analyse data including identification of risk factors for introduction of infection (M24-36)
- M10 Hold meeting to disseminate project findings (M36)
Outputs to AgriSearch (with timescales): (i.e. Progress reports, final report, farmers booklet)
- Deliverable 1 DARD studentship. (M0)
- D2 Year 1 report (M12)
- D3 Year 2 report (M24)
- D4 Final report (M36)
- D5 Open meeting (M36)
- D6 Press releases on research findings (M12-36)
- D7 Peer reviewed publications (M24-36)
- D8 PhD Thesis (M42)
Benefits to industry: (Non monetary)
The project will have a directly beneficial effect on the participating herd owners with results being reported back to them in real time through the course of the project. During the course of the project these herd owners will become familiar with the rationale and practical application of methods of diagnosis and control, and it is hoped they will become champions of this approach to the wider industry. The industry generally will benefit from the knowledge gained during the project, with new relevant information on disease prevalence, breakdowns and factors contributing to this. The project will provide access to new advanced and cost-effective screening methods validated during the project. Industry will also have a better understanding of the performance of current vaccination strategies.
Potential financial value / economic benefits to the Northern Ireland farmer:
As described above, BVDV is widespread in NI dairy herds, with recent or current infection in the majority of herds. While it is not possible to accurately quantify the economic benefits, application of these tools at herd level will result in significant financial savings due to avoidance of losses due to infection. A conservative estimate of the cost of BVDV to the NI cattle industry over the past 8 years is £5m.
Technology transfer: (How will this work be disseminated to local farmers?)
A variety of methods will be used to communicate the findings to local farmers. These will include:
- Articles in the popular press (e.g. Farm Life, Farmer’s Journal)
- Meetings with farmer groups, discussions groups UFU etc. In order to communicate key facts on BVDV control and eradication to an NI audience, a public meeting will be held for key stakeholders at the end of the project. This is anticipated to include farmers and their representative bodies, veterinary surgeons and their representative bodies and other stakeholders e.g. milk purchasers and processors.
- One on one discussions with participating herds and feedback to these herds through e.g. diagnostic reports, written summaries of the findings.
- Annual project updates to Agri-search.
- In addition, it is envisaged that the results of the work will be subjected to scientific peer review through publication in refereed journals and presentation at conferences.