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Bovine viral diarrhoea (BVD) is a pestivirus infection of cattle. It causes a variety of clinical outcomes ranging from the inapparent (sub-clinical) to the more severe, including abortion, infertility, an immuno-suppression that underlies calf respiratory and enteric diseases, and most dramatically, the fatal mucosal disease.

Challenge

The disease is maintained by a small population of animals that become persistently infected (PI) with the virus. These PI animals are the major reservoir of BVDV and arise after becoming infected whilst in the uterus during early pregnancy. Such infections remain throughout the pregnancy and, after birth, for the lifetime of the animal. Although infection of the foetus results in a persistent infection, the mother is only transiently infected and becomes immune to the virus within 2-3 weeks.

PI calves often die prematurely with respiratory or enteric disease but may also live a relatively normal life for several years – all the time shedding large amounts of virus and acting as a reservoir of infection for in-contact cattle.

Thus, PIs are the main and most significant source of infection of BVD virus. Removing PIs from the population removes the source of infection and reduces the disease reproduction rate to the point that the virus cannot survive – and the disease is therefore controlled. There are other methods of virus maintenance and transmission, but they are considered of lesser significance in maintaining the disease.

The virus survives poorly in the environment, and has no significant survival in other species e.g. other livestock or wild animals. With this epidemiology understood, it is now possible and practical to control and eradicate BVD from cattle populations.

Good diagnostic tests exist to detect both the PI animals and also the antibody status of the herd (i.e. to indicate whether BVD virus is present and circulating within a group of cattle). Good vaccines exist to protect breeding cattle and prevent the creation and birth of PIs. This disease is now eminently controllable.

This endemic viral disease of cattle is common in the UK and causes significant losses. Herds with BVD suffer infertility and reproductive disorders. Their health is poor, with problems such as pneumonia and scour. The disease may be insidious and protracted – you get used to living with the problem in the herd, to the point where you don’t realise how badly it affects you – until it is gone.

Solution     

Many farmers do not realise that their herds are infected, and those that aren’t infected may be at significant risk of becoming so, with potentially disastrous consequences. It is possible to control BVD at farm level, and the disease could be eradicated – if the industry as a whole co-operates.

Many other European countries have embarked upon control and eradication schemes, with rather more success than the UK. Norway, Sweden, Finland and Denmark have now virtually eliminated BVD from their national herds.

BVD control and eradication is relevant for any farm, whether the disease is there or not. Even if a herd is uninfected it needs protection, as introduction of BVD into a herd that has not been previously exposed to BVD could be disastrous. As more and more herds become clear of infection, protection becomes easier as the risks of infection reduce.

Impact     

BVD is one of the most devastating diseases of cattle – for the animals themselves and communities dependent on them around the world. The RVC has had a considerable impact on understanding and developing ways to tackle BVD. Joe Brownlie, Emeritus Professor of Veterinary Pathology at RVC, and scientists he has supervised and veterinarians he has trained and worked with, have contributed significantly to the fight against the disease.