What is BVD?
Bovine Viral Diarrhoea (BVD) is caused by the bovine viral diarrhoea virus (BVDV). The genus Pestivirus of the family Flaviviridae consists of four recognised species: Bovine viral diarrhoea virus type 1 (BVDV-1), Bovine viral diarrhoea type 2 (BVDV-2), Border disease virus (BDV) and Classical swine fever (CSF) virus .
Pestiviruses are single stranded positive-sense RNA viruses. Although the natural host for BVDV is cattle, it can also affect sheep and wild animals, including deer and pigs.
The cost of BVD to the industry
BVD is recognised as one of the most economically important endemic diseases of cattle. Several estimations on the cost that infection with this disease can inflict have been produced in other regions/countries but these are dependent on the characteristics of the industry, including cattle density, prevalence of the disease, and cattle movements.
A study carried out by the Scottish Agricultural College (SAC) for Animal Health Ireland in the Republic of Ireland (RoI) is of more relevance to our industry and showed that prior to the eradication programme, BVD was costing the industry in the RoI at least €102 million per year. This comprised of €55 million dairy, €27 million suckler and €20 million in the finishing sectors respectively. At the animal level this is equivalent to €48 per year for every dairy cow and €30 per year for every suckler cow. These figures show clearly the significant losses suffered by Irish producers due to BVD virus.
Possible outcomes of infection with BVD virus in susceptible cattle can result in failure to conceive, abortions, malformed foetuses, stillbirths and the birth of persistently infected (PI) carrier calves. PI calves are born when susceptible dams are infected with BVD virus in the first 4 months of pregnancy and they are typically antibody negative and virus positive. These animals usually die in the first 24 months of life from mucosal disease showing clinical signs of severe diarrhoea and ulceration of the mouth and feet. However, others will look clinically normal and may lead a normal life.
PI animals are very efficient transmitters of BVD virus and are the main source of infection to other cattle which can then experience a temporary weakening of their immune system. This is particularly important in calves, and may result in increased levels of pneumonia and diarrhoea. Persistently infected bulls are excluded from AI centres due to the presence of virus in their semen.
In summary, infection with BVD can result in a wide range of clinical signs including:
- Weakening of the immune system, leaving cattle more susceptible to other infections.
- Scours and pneumonia in calves due to immunosuppression.
- Reproductive problems, including failure to conceive (infertility),early embryonic death, abortion and birth defects.
- Calves that survive infection during early pregnancy are born persistently infected (PI) with the virus. Many will develop a fatal condition called mucosal disease in the first two years of life.
How is BVD introduced in a herd?
- Buying PI animals (antibody negative, virus positive).
- Buying pregnant cows carrying a PI calf (antibody positive).
- Contact: over the fence, shows, break in/out, co-grazing.
- Visitors and equipment.
How can BVDV be controlled?
The key for control of BVDV in a herd is the identification and removal of persistently infected animals. In addition, biosecurity measures must be put in place. These should include at a minimum testing and isolation of added animals and stockproof boundaries.
AFBI Cattle Health Scheme includes BVD programmes which will provide clear steps to follow with a view to control the disease and obtain accredited status. For more information: AFBI Cattle Health Scheme
How to test for BVDV
A range of tests and strategies are available for the screening of dairy and suckler herds for BVD virus. These should be discussed with your veterinary surgeon.
If you are based in the Republic of Ireland, please go to the RoI Eradication scheme - Testing at AFBI section.
Testing for antibodies
- Antibody test in blood by enzyme-linked immunosorbent assay (ELISA)*
- Antibody test in milk (individual and bulk) by ELISA*
Testing for virus
- Antigen by ELISA: blood and ear notch*
- Virus isolation: tissues, swabs, semen (requirement for some bulls going into an AI station)
- Immunofluorescence (IFAT): swabs
- Real time reverse transcription polymerase chain reaction (RT-PCR), normally referred to as ‘PCR’: blood, ear notch, tissues, swabs, semen*
* Tests accredited to ISO17025 standard
Testing of individual animals
Persistent infected (PI) animals:
Calves are born PI after surviving infection in early pregnancy (between 30 and 120 days). Will be excreting large quantities of virus all their lives and will be the main source of infection for other animals. They can look normal but they also may be stunted or ill-thrifty. The majority will develop a fatal condition called ‘Mucosal disease’ characterised by severe diarrhoea. This typically occurs when the animal is between 6 to 18 months.
Transiently infected (TI) animals:
Infection with BVD is usually mild but it can cause suppression of the immune system and make the animals more susceptible to common infections typically scour or pneumonia or both. Animals will develop life-long immunity.
BVD Eradication Programmes
Several European countries have been successfully implementing systematic control of BVDV for a number of years. Sweden, Norway, Finland and Denmark are virtually free of the disease. Austria and Switzerland also have successful national programs.
In the UK systematic control has eradicated BVDV from the Shetland Islands. Key factors for the success of systematic control have been identified and include education on biosecurity, joint efforts of government, vets and farmers and legislative support for movement controls.
These programs have succeeded using the zoo-sanitary approach, with and without the use of vaccine.
Details of the BVD eradication programme in Northern Ireland can be seen at the NI BVD Eradication Programme section.
Details of the National BVD eradication programme for the Republic of Ireland can be seen at the RoI Eradication scheme - Testing at AFBI section.
The Scottish Government committed to eradicating BVD with a programme consisting of four phases. In the first one, which started in September 2010, testing was supported for breeding herds with some financial help and an awareness programme was launched. Supported test ended on March 2011.
In September 2011, the second phase was initiated. All cattle herds in Scotland were required to test annually for BVD from the 1st December 2011. From September 2012 movement restrictions were l applied to herds infected with BVD.
Phase 3 was launched in January 2014 making it illegal to move a PI animal. Phase 4 currently underway brings in further control measures which restrict ‘not negative’ herds.