5 Aug 2019
Paul Wood
Job Title
Image © stefanholm / Adobe Stock
Bovine viral diarrhoea (BVD) is a highly contagious viral disease of cattle and still one of the biggest disease problems affecting the UK cattle industry.
BVD virus (BVDV) can have immunosuppressive effects and cause reproductive failure, which can lead to increases in other costly diseases – such as pneumonia and diarrhoea – and can affect pregnancy rates. BVD can, therefore, have significant impacts on welfare, as well as the financial success of an enterprise.
The cost of the disease to the national herd is quoted as being between £25 million and £61 million per year (Agriculture and Horticulture Development Board, 2019); however, the costs to individual farms will be highly variable.
Cattle exposed to BVDV may show few clinical signs. In dairy cows, it may result in a temporary drop in milk yield. The immunosuppressive effects of BVDV may lead to common clinical syndromes occurring more frequently and more severely, particularly in young calves.
During early pregnancy, BVD can cause embryonic death and return to oestrus, fetal death/abortion, mummification of the fetus or weak/premature calves, as well as birth defects of the nervous system and eyes.
Infection of the fetus before approximately 110 to 120 days of pregnancy results in the birth of a live, but persistently infected (PI), calf. This is due to the failure of the developing immune system of the fetus to recognise the virus as foreign and, therefore, it becomes immunotolerant of it. PI calves typically fail to thrive and tend to be noticeably poorer than their age cohort. Although the PI calf is infected for life, the dam is only transiently infected – developing immunity to the virus in three to four weeks.
Chronic infections have been described in bulls, with the virus localised to the testes and the disease transmitted successfully to cows by AI (Newcomer et al, 2014). It is not believed these chronic infections represent a significant risk of transmission (Givens and Marley, 2013).
Mucosal disease occurs when PI animals become “superinfected” with cytopathic BVDV. This occurs due to changes in the BVD virus within the PI animal or by infection by a cytopathic strain.
This disease syndrome is most commonly seen in calves aged 6 to 12 months. Clinically, they appear depressed with an accompanying fever and anorexia. Ulcers appear in the mouth and muzzle, which can lead to excessive salivation. Purulent discharge from the eyes and nostrils is observed and profuse diarrhoea is present (with shreds of gut mucosa and blood present during the end stages). Ulcers can also develop on the coronary band or interdigital skin, resulting in severe lameness. Rapid weight loss occurs and death often follows within 5 to 10 days.
BVDV is maintained within a cattle population by PI animals and can be spread directly (from the infected individual) or indirectly (by contaminated visitors or equipment).
PI animals can survive for several years, providing a constant reservoir of virus for any in-contact animals. Identifying and removing PI animals is the key element of eradication schemes for BVD – one PI animal introduced to a susceptible herd can lead to significant losses.
The virus generally survives poorly in the environment, but has been demonstrated to survive in slurry for three weeks (Bøtner and Belsham, 2012). Under both experimental and field conditions, BVDV has been found to be carried and spread to cattle by sheep, goats and deer (Passler and Walz, 2010); however, the significance of this route of transmission is thought to be low.
Diagnostic tests are available to detect both the PI animals (viral antigen) and the antibody status of the herd (indicating if BVD virus is present and circulating within a group). Blood, milk and skin biopsies can all be used for BVDV testing, depending on the aims of testing and the preferred method for the individual farm.
Cattle Health Certification Standards (CHeCS) is the regulatory body for cattle health schemes in the UK and Ireland.
CHeCS was established in 1999 by the cattle industry to control and eradicate a range of diseases using a set of standards to which all licensed cattle health schemes must adhere.
CHeCS’ principal objectives are:
These standards ensure herd health status across schemes is equivalent in the UK and Ireland.
CHeCS does not run any health schemes itself, but sets the standards for CHeCS-licensed cattle health schemes in the UK, including:
As aforementioned, BVD control and eradication is relevant for every UK cattle farm, regardless of whether disease is present.
Uninfected farms need protection, as incursion of disease into a naive herd can be disastrous. As an increasing number of herds become clear of infection, it is easier to protect animals because the risk of infection reduces.
Control and prevention can only be achieved through strict biosecurity procedures, vaccination and long-term control strategies. This is further detailed in many of the aforementioned schemes.
One inactivated and one modified live BVD vaccine are available in the UK – the vaccination protocols for each are described in Table 1.
| Table 1. Vaccine protocols for UK BVD vaccines | |||||||
|---|---|---|---|---|---|---|---|
| Product name | Vaccine type | Manufacturer | Primary course | Repeat vaccination | Comments | ||
| Bovilis BVD | Inactivated | MSD Animal Health | Individual: two IM injections four weeks apart | Herd: two vaccinations four weeks apart in all animals older than eight months | Individual: one vaccination four weeks before start of next gestation | Herd: one vaccination six months after basic vaccination, with next revaccinations an an interval no greater than 12 months | Second vaccination of primary course should be given not later than four weeks before start of gestation |
| Bovela | Modified live | Boehringer Ingelheim | One dose by IM injection | Annual booster | Recommended primary vaccination at least three weeks prior to breeding | ||
| Note: the above protocols are taken directly from each product’s summary of product characteristics and licence. Contact the manufacturer for further clarification or protocol design you require. | |||||||
By working closely together with farmers, other veterinary professionals, government agencies and breed societies, we can all make valuable contributions to the eradication of this costly disease. If all breeding females in the UK herd can be vaccinated at the appropriate time, this will control disease by preventing the infection of the developing fetus during pregnancy and, thereby, stopping the production of PI calves.
