Bovine viral diarrhoea (BVD) is an infectious disease of cattle caused by an RNA virus of the genus Pestivirus, belonging to the family Flaviviridae. Infection of cattle with bovine viral diarrhoea virus (BVDV) is associated with immunosuppression, reproductive failure, and other more variable signs, such as decreased milk production, reduced weight gain, fever, diarrhoea and respiratory disease. The immunosup-pression can allow other infectious agents to become established and exacerbate respiratory and other diseases (Lanyon, 2014).
If infected for the first time during pregnancy the BVDV can cross the placenta and infect the fetus, which may lead to embryonic death, congenital defects or, if infected before day 130 of pregnancy, the birth of persistently infected (PI) calves. PI animals shed BVDV in all excretions and secretions throughout their life and are the primary route of transmission of the virus. BVDV control programmes such as BVDFree England aim to eliminate PI cattle and thereby the source of continuing infection (Lindberg and Alenius, 1999).
One of the main drivers of BVD control programmes is the economic impact of BVD. Estimates range from £0 to £552 per cow per year, with a mean impact of £46.50 (Yarnall and Thrusfield, 2017). A review of economic impact research estimated a cost of between £6.46 and £87 per cow per year in endemically infected herds, with outbreaks in naïve herds ranging from £28.50 up to £2370 per cow per year, with a severe outbreak of virulent virus (Yarnall and Thrusfield, 2017).
Control of infectious diseases
The global pandemic of SARS-CoV-2, the virus that is the cause of the serious life-threatening disease known as COVID-19, has focused attention on the control of infectious diseases in people and in animals. The Foresight project: Infectious Diseases: preparing for the future report (Brownlie, 2006) identified a concern that, over the next 25 years, humans, animals and plants would be threat-ened by completely new infections, as well as continuing to suffer from those that are already known. There was also the experience of infections with SARS-CoV-1 virus during 2002–2003 and foot- and-mouth disease in 2001. Despite these red flags and with the benefit of hindsight, global and UK preparedness for control of a novel infectious agent was woefully inadequate.
The general who wins the battle makes many calculations in his temple before the battle is fought. The general who loses makes but few calculations beforehand
— Sun Tzu
However, the speed of response in some areas has been truly impressive and driven by advances in science over the last two decades since the SARS-CoV-1 virus was identified. The identification of the SARS-CoV-2 virus, the sequencing of its genome, the sharing of that sequence, the development and deployment of tests and of vaccines and epidemiological modelling have all been achieved within a remarkably short timeframe. Finding solutions to technical challenges is less about the range of tools we have and increasingly more an issue of financial, human and other resources.
In contrast some of the flaws in the management of the disease have been exacerbated by failures in the speed and intensity of reaction to contain the spread of the virus. Lessons, particularly in basic biosecurity, biocontainment and surveillance have not always been learned. An early example was the assumption that people who were asymptomatic or pre-clinical were not a major source of virus spread — absence of evidence is not evidence of absence and not ‘science led’. The rapid evolution of the SARS-CoV-2 virus has exposed and exploited weaknesses. As should already have been clear, infectious diseases operate on their own terms and take any opportunities offered to exploit loopholes. Viruses do not wait 4 days for borders to close before taking opportunities to infect and to spread.
It will be interesting to see how many of the lessons learned in a review of the COVID-19 pandemic in the UK reflect the lessons that were not learned from the outbreak of foot-and-mouth disease in 2001.
When you point your finger cos your plan fell through You got three more fingers pointing back at you
— Dire Straits
At a time when there is intense focus on the control of infectious disease it is appropriate to take an objective look at the progress with the programmes for the elimination of BVDV in the British Isles.
There are good diagnostic tests for BVDV, effective vaccines and a good knowledge of the epidemiology of the disease. There are no real technical barriers to the elimination of BVDV from cattle herds on a national or regional basis. The first national BVD elimination programmes started in Scandinavia in the 1990s and voluntary programmes started in the British Isles in the 2010s.
The challenge is to deliver an integrated programme that engages all farmers, veterinary surgeons and other stakeholders in action to eliminate BVD. The three key elements of a programme to eliminate BVDv are:
- Identification and removal of PI animals
- Biosecurity measures to prevent introduction of BVDV
- Ongoing monitoring to ensure that uninfected herds remain free from infection.
BVD elimination programmes
England
BVDFree England was launched in July 2016 building on earlier activity funded through the Rural Development Programme for England (RDPE). BVDFree Ltd is an industry owned company and receives no government funding. The only source of funding is an upload fee for adding test results to the BVDFree database and this is used to fund the database and helpdesk. The Agriculture and Horticulture Development Board (AHDB) provide in-kind support in managing the project on behalf of BVDFree Ltd.
At the end of 5 years, July 2016 – July 2021, 6500 herds had registered with BVDFree representing close to an estimated 45% of the national cattle breeding herd in England. Over 70% of herds were recruited through the Stamp It Out BVD initiative funded through RDPE, which started in July 2018 and closed for on-farm activity in June 2021. Herd status can be established by blood testing youngstock for BVD antibody or testing all calves for BVDV. Holdings that register for BVDFree agree to test annually for the presence of BVD, but less than 50% of all BVD-Free registered holdings uploaded a test result in 2020. Holdings that have demonstrated evidence of absence of BVD for 2 years through testing can apply for BVDFree test negative herd status. There were 725 herds (11%) with BVDFree test negative herd status in June 2021.
Isle of Man
In the Isle of Man, since 2014, all calves, including dead and still-born, must be tested for BVDV using official ear tissue tags. No animals are listed as having tested positive since 2019 (9394 calves registered in 2019). There were 128 animals of unknown status in mid-2021 (Isle of Man Government, 2021).
Ireland
In Ireland it has been a legal requirement, since 2013, to tissue tag-test all calves for BVDV. Measures have been reviewed and updated on an annual basis and communicated to farmers and veterinary surgeons. In 2020 to end June 2021 0.03% of calves have tested positive. At the end of June 2021 0.39% of herds were classified as positive for BVD (Animal Health Ireland, 2021).
Northern Ireland
In Northern Ireland it has been a requirement since March 1 2016, to tissue tag-test all calves. The rolling annual percentage of animals that have tested positive for BVDV was 0.29% at the end of February 2021. The herd level prevalence (herds with initial positive or inconclusive results in previous 12 months, up to February 28 2021) was 4.2% (Animal Health and Welfare Northern Ireland, 2021).
Scotland
The Scottish government has supported an industry-led scheme to eliminate BVDV from Scotland since 2010. The BVD programme became mandatory in 2013 and since January 2014 it has been a legal requirement to declare the status of the herd or animal at the point of sale. A phased approach has been taken, gradually increasing restrictions on cattle herds that have evidence of disease, with the goal of protecting BVD negative herds (Scottish Government, 2019). Herd status can be established by blood testing youngstock for BVD antibody or testing all calves for BVDV. In January 2021 approximately 90% of herds with breeding animals in Scotland were negative for BVD (Purcell, 2021).
Wales
Gwaredu BVD, funded by the Welsh Government's Rural Development Programme, started voluntary testing in September 2017. Over 75% of cattle farms in Wales had been screened by January 2021 by testing a minimum of five cattle in each management group of 9–18 month old youngstock for BVD antibody. Where there is evidence of seroconversion, funding is available for testing to identify animals in the herd PI with BVDV. Of the 8601 farms screened by January 2021, 26% were positive for BVD antibodies. A total of 675 PI cattle have been identified on the 728 farms that have undertaken a PI hunt. Fifty per cent of PIs have been retained on farm, 25% slaughtered and another 25% have been moved off farm other than to slaughter (Paton, 2021).
CHECS
CHECS (formerly known as Cattle Health Certification Standards) has been setting industry standards for cattle disease control since 1999. Farmers can join CHECS licensed health schemes to accredit the BVD status of their herds. Herds fully participating in CHECS BVD programmes meet the testing requirements of the BVD programmes in England and Scotland. Herds must also meet CHECS biosecurity standards to be accredited as free. In Scotland and England the highest BVD herd status is for herds accredited as BVD negative by CHECS.
Persistent infection with bovine viral diarrhoea virus
Early identification and prompt action is key to the control of infectious diseases. The core of BVD elimination programmes is identification and removal of cattle born PI with the BVDV (Figure 1). PI animals are more susceptible to other diseases, which may be fatal, to ill thrift or to death from mucosal disease (Houe, 1993). Mucosal disease is the result of co-infection with both the non-cytopathic and cytopathic strains of the virus. Some PIs can survive for years shedding large amounts of virus. Removal of PI cattle from herds as quickly as possible minimises the time during which further spread of the virus can occur.
Keeping PI cattle on farm increases the likelihood of finding an animal positive for BVDV in the herd in the next calving season (Graham et al, 2015).
Animal Health Ireland used programme data and modelling of scenarios to show eradication was not achievable within a realistic time window if retention for more than 7 weeks continued at the levels seen in Ireland in 2015 (30%) (Graham, 2021). In Ireland PI retention was addressed by measures including financial incentives to encourage early removal, herd-level movement restrictions, ongoing programme communications and the input of private veterinary practices. Structured investigations by veterinary surgeons in positive herds were developed to identify plausible sources of infection, to resolve the status of all animals in the herd and to agree up to three measures to prevent re-introduction of the virus (Graham, 2021).
In Scotland breeding herds that have been BVD not negative for more than 15 months must undertake a compulsory BVD investigation and must obtain an individual BVD negative status for each animal to ensure any PIs are identified. BVD positive animals must be housed separately from other cattle, and keepers cannot bring cattle into BVD positive herds.
The duration and cost of any BVDV elimination programme will be heavily influenced by the speed of identification and removal of PI animals. PI animals are identified at birth in programmes that require all calves to be tissue tag tested for BVDV before official registration. A whole herd PI hunt is required to identify PI animals in herds following a positive youngstock checktest. Programmes need to weigh up which strategy will lead to more rapid removal of PIs in practice.
Biosecuiryt
Spot the deliberate mistake — when it comes to biosecurity most farmers are dyslexic in its application! While many farmers recognise the value of closed herds for preventing the introduction of BVD, some farmers who purchase from a ‘reputable source’ often still categorise their herds as ‘closed’ (Azbel-Jackson, 2018). While farmers are constantly bombarded with messages to improve the nebulous concept of biosecurity, it is interesting to note the almost complete absence of the term in communications regarding COVID-19. Yet ‘Hands, Face, Space’ are essentially simple expressions of fundamental biosecurity measures to minimise the risk of spread of infection.
The aim of biosecurity is to keep negative herds negative by preventing the introduction of infection. Movement restrictions have been an integral part of protecting herds from the risk of buying in BVDV in the mandatory BVD elimination programmes. In Ireland herd restrictions are now imposed immediately for herds with BVDV positive or inconclusive results and neighbouring herds immediately receive a biosecurity notification informing them of their increased risk. In Scotland BVD positive herds are listed by CPH number in a PI locator list when an animal identified as a PI is still in the herd 40 days after the result was uploaded.
The BVD Implementation Group in Northern Ireland has been asking government to bring in new legislation that would allow information on BVD breakdowns to be shared with at-risk herd keepers, to encourage the application of targeted biosecurity measures that will help to reduce the risk of the BVDV entering their herds.
In contrast in the voluntary programmes, Gwaredu BVD in Wales and Stamp It Out BVD in England, not only is there an issue with retention but animals identified as PIs with public monies can and are being moved, potentially fuelling the spread of BVDV. Herds registering with BVDFree in England agree not to move PI animals other than directly to slaughter. However, BVDFree currently has no mechanism to check compliance.
The risk from retention of PIs increases the risk of infection on neighbouring farms. In Ireland when models were used to estimate the risk of a herd having BVD positive calves in 1 year, when contiguous to a herd that had at least one BVD positive calf born in the previous year, the Odds Ratio associated with having ‘a PI-neighbour’ farm was 1.92 (95% C.I. 1.37–2.70) (Graham et al, 2015). Ensuring social distancing at boundaries with neigh-bouring farms can help reduce the risk of infection but there is little information on the proportion of farms with double fencing. In England plans for sustainable farming incentive payments for hedgerows could potentially help increase social distancing on cattle farms.
The other key potential route for introducing BVDV is bringing it on to the farm on people, tools, equipment or any other contaminated product. Here the issue is one of cleaning and disinfection to a sufficiently high standard to kill the virus. As with hand washing for COVID-19 this will be to a higher standard than is normally practised.
Vaccination
BVDV vaccines can be used to induce a protective immunity in breeding animals to minimise the risk of effects on reproduction, including failure to conceive, abortion, birth defects and most importantly the creation of calves that are PI with BVDV. Vaccination is an additional protective measure should there be a breakdown in biosecurity. BVD vaccines do not provide 100% protection in all circumstances (Antos, 2021), even when stored and used correctly, particularly where pregnant cattle are exposed to high levels of BVDV. Vaccination alone will not achieve BVDV elimination at herd level or at national level.
Monitoring and surveillance
In Ireland and Northern Ireland every calf born has been required to be tested since 2013 and 2016 respectively. In Scotland herd screening has been mandatory since 2013. Further investigation is required to identify the potential source of infection if a BVD seropositive animal(s) is/are present on the farm.
When PI calves are identified shortly after birth the dam will have been infected with BVDV between 5 and 9 months previously. At the start of a BVD tag and test programme PI animals not tested as calves may not be picked up until they calve down at 2–3 years of age.
The recommended minimum age of youngstock at the time of testing is 9 months. If a 9-month-old animal is antibody positive it has been infected with BVDV in the last 1–9 months (allowing 28 days for sero-conversion). If the source of infection for a 9-month old animal is a cohort PI animal in the youngstock group its dam may have been infected with BVDV up to 18 months earlier. A full herd test will be required to identify if PI animals are present in the herd.
Gwaredu BVD aims to integrate its herd screening programme with the annual tuberculosis (TB) test for cattle herds. Certificates are available to all herds that screen clear of BVD — bronze after one clear screen; silver after two consecutive clear screens and gold to farms that have screened clear on three or more consecutive years’ testing. (Gwaredu BVD, 2021).
Herds registered with BVDFree in England can apply for BVD-Free test negative herd status if they have 2 consecutive years of negative test results. Annual screening is required to maintain the BVDFree test negative herd status.
Communications and stakeholder engagement
Communications and stakeholder engagement and cohesion are also key to successful BVD elimination. All of the programmes have strong industry support and involvement. Only BVDFree lacks any formal direct involvement of government.
Animal Health Ireland is a partnership between private sector organisations and businesses in the agri-food sector and government. The decision-making body for the BVD programme in Ireland, the cross-industry BVD Implementation Group, meets on an approximately monthly basis. A separate Technical Work Group provides ongoing scientific advice. The programme appears to be scienceled with analysis and modelling acting as the catalyst for decision-making on next steps to drive elimination. The broad portfolio of peer-reviewed scientific publications has created a valuable resource for others planning national BVD elimination programmes. There has been no hiding from reality and programme results are openly published on their website with useful maps showing distribution of BVD-positive births during each year of the BVD eradication programme (Animal Health Ireland, 2021). An annual update of key messages for farmers is also made available through their website along with a range of useful resources. The recent recruitment of a health psychologist to focus on applying behavioural science to animal health programmes is another illustration of the ongoing drive and commitment to communication of Animal Health Ireland.
Animal Health and Welfare Northern Ireland (AHWNI) 2021 and Isle of Man Government (2021) publish and update key programme statistics but no information is easily available on the progress of the other programmes. Information on BVD and on the programmes is available on webpages for all programmes.
There has been concrete industry support for the BVD programme in Northern Ireland. In 2018 farming unions reached an agreement with the Northern Ireland Meat Exporters' Association to ban PI cattle from slaughter plants. In 2020 The Livestock and Meat Commission took a decision to suspend farm quality assurance status of herd owners that retain PI BVD animals in their herds.
Scottish government sees its role as one of supporting the ambitious industry-led scheme in Scotland. The mandatory BVD programme was introduced in Scotland at the request of cattle industry stakeholders.
Gwaredu BVD have worked closely with the Wales Animal Health and Welfare Framework Group and Welsh government on design, development and delivery of the voluntary BVD programme. Welsh government provided £10 million in funding to Gwaredu BVD for BVD control in around 11 000 herds in Wales. Gwaredu BVD has particularly focused on communications to veterinary surgeons to drive engagement, but has also maintained communication to farmers.
BVDFree had broad cross-industry organisation support when the programme was launched in 2016 but has struggled to maintain momentum with the broader stakeholders. BVDFree Ltd is owned by the National Farmers Union, the National Beef Association, the Cattle Information Service/Holstein UK, the British Cattle Veterinary Association, the Livestock Auctioneers Association and the Agriculture and Horticulture Development Board. BVDFree has the weakest level of direct engagement with government. The £5 million in RDPE support for BVD control in over 35 000 herds with breeding cattle (Department for Environment, Food and Rural Affairs, 2021) was delivered through a separate initiative, Stamp It Out BVD. The aim of that initiative was to engage at least 50% of the dairy and beef breeding herd in England in BVD control by the end of June 2021.
A new Red Tractor farm assurance standard for dairy farms introduced in October 2019 requires BVD to be managed through a BVD eradication programme (which can be one of the national programmes) designed in conjunction with the farm veterinary surgeon. A number of retail supply chains also require dairy farms to engage in BVD control. There are currently plans to introduce this as a Red Tractor standard for beef in 2022.
A crystal ball
Freedom from BVDV is the objective of all the BVDV elimination programmes. However, the difficulty of achieving complete freedom should not be underestimated. Of the programmes in the British Isles, the Isle of Man may be closest to elimination of BVDV not having reported any positive cases since 2018, but the status of a small number of animals is unknown.
Ireland is working towards recognition of its programme by the European Commission under the new EU Animal Health Law with the goal of achieving freedom by 2023. At least 99.8% of herds and 99.9% of animals would have to be negative to be recognised as free. The programme would then enter a surveillance phase. Sweden's BVD programme started in 1993, herd testing became mandatory in 2001 and it identified its last case in 2011 (van Roon, 2020). If Ireland can achieve its objective the mandatory phases of both programmes would have taken 11 years, despite using entirely different approaches.
Northern Ireland's current animal and herd level prevalence and rate of retention of PI animals is similar to that in Ireland in 2015–6. This suggests that without a step-change it may be difficult to achieve its stated intention of freedom by end 2023. Given that its programme essentially replicates the programme in Ireland and that its mandatory phase started in 2016, it may be more realistic to expect freedom to be achieved in a similar timeframe, i.e. by 2026.
The programme in Scotland became mandatory in 2013 the same year as the programme in Ireland. Around 10% of herds are not negative but this may include herds that are negative, but have not complied with programme requirements within the last 12 months. Using information from within the programme and the experience of the other programmes in Europe, it should be possible to model the potential outcome of the current programme and to explore scenarios as has been done in Ireland (Thulke, 2018). A key conclusion of that work was that ‘Investment in rigorous quantitative assessment does prevent misguided calls for action’.
Gwaredu BVD has achieved an impressively high level of penetration for a voluntary programme. In part this reflects the success of the strategy of integrating the screening into the annual TB testing of cattle herds, the fact that the testing was free at the point of delivery, the engagement of the veterinary surgeons and the quick turnaround of results allowing veterinary surgeons to be in a position to communicate the outcomes on day 2 of the TB test. There are lessons to be learned from the experience which could have potential applications elsewhere in voluntary control programmes for infectious diseases. One concern surrounds the use of public funds to identify PI animals that have then been moved off farm potentially resulting in virus spread. The Gwaredu BVD steering group has submitted a paper to Welsh government requesting legislation to continue the work carried out by veterinary surgeons and farmers towards BVD freedom (Paton, 2019). The extension of the Gwaredu BVD programme to end-2022 allows time for a quantitative assessment of the options for a mandatory programme.
In England the BVDFree Board have sought the support of Ruminant Health and Welfare for a transition to a mandatory programme of BVD elimination. In the absence of a mandatory programme there is no realistic likelihood of ever achieving BVD elimination. On 30 June, 2021 an update on the government's Agricultural Transition Plan (Defra, 2021) indicated that as a first step on the Animal Health and Welfare Pathway, Defra will fund a yearly visit from a veterinary surgeon or veterinary-led team to carry out an annual health and welfare review. It also outlined plans to support testing for BVDV. Without movement restrictions and prompt removal of PI animals the risk is that there would be little change in BVD prevalence from this investment of public funds.
Industry ambitions for elimination of BVDV from the UK by 2031 (Ruminant Health and Welfare, 2021) should be achieved in Northern Ireland with time to spare. Elimination by 2031 should be feasible in Scotland if retention of PIs and compliance with monitoring can be addressed. In Wales it could be possible if a mandatory programme is introduced and the momentum achieved to date is maintained, but it might need another couple of years.
A swift rethink is needed in England as 2031 would be a stretch target for BVDV elimination. It is not impossible as the wealth of experience, internal data and data from other programmes should mean policy and a strategy could be formulated for BVDV on the basis of sound scientific quantitative assessments that help identify a pathway to successful elimination. What would still then be needed is a focus on the 3Cs of culling (PIs), commitment (to driving the strategy) and communication (communication, communication…repeat).
Effort in all parts of the UK would be undermined if prevalence remains high in any one area, seeding infection. There is also a risk of confusion when moving animals between different parts of the British Isles if there is not mutual recognition of the BVD status of individual animals and/or herds. The programmes have been meeting annually, since 2016, to discuss issues of mutual interest and the challenges of eliminating BVDV. Additional precautions to protect the investment in BVDV elimination may be justified as programmes approach the point of BVDV elimination.
BVD freedom can be achieved if all stakeholders play an active part and the role of veterinary surgeons in engaging farmers and delivering the programmes is one of the keys to success.
Conclusion
BVD is well understood disease, not least because of research by Joe Brownlie, Richard Booth and others in the UK and internationally and there are good tests. Good programmes can be designed based on available data and focused application of scientific modelling.
The key measures are to identify animals PI with BVDV, remove them as quickly as possible and then take strong steps to ensure BVDV is not introduced into herds free of the virus. The difficulty lies in delivering a programme with the intensity and focus required to maintain freedom. Half-hearted efforts only deliver half-baked solutions and BVDV will take advantage of any weaknesses.
The support and engagement of veterinary surgeons and farmers is critical and voluntary programmes can make good progress. However, elimination within a realistic timeframe is only possible with mandatory programmes which reach all farms and with mandatory controls on the movement of PIs. The Republic of Ireland is tantalisingly close to achieving recognition of freedom from BVDV by 2023, 11 years after their programme became mandatory.
To paraphrase Joe Brownlie at BCVA 2017 – if you want to eliminate BVD you need either a bl***y great carrot or a tiny stick!
KEY POINTS
- Bovine viral diarrhoea virus (BVDV) elimination from cattle herds in the British Isles is technically feasible.
- Identification and rapid removal of cattle persistently infected with BVDV is the key step.
- Key supporting measures are strict biosecurity to prevent reintroduction of BVDV and regular monitoring to identify breakdowns.
- Vaccination reduces the risk of disease but does not eliminate the risk of infection persisting in herds.
- Science could be applied more effectively in the design and delivery of bovine viral diarrhoea (BVD) elimination programmes as in Ireland.
- Focus, commitment, drive and good administration and good communications are key to achieving elimination.