Bovine Viral Diarrhoea {BVD}

Bovine Viral Diarrhoea (BVD)

BVD is a viral disease of cattle caused by a pestivirus (similar to Border Disease virus in sheep and swine fever virus in pigs). It has many different manifestations in a herd, depending on the herd’s immune and reproductive status. Transient diarrhoea, mixed respiratory infection, infertility or abortion and mucosal disease are the most common clinical signs of the disease and can be seen simultaneously in a herd. Due to its varied manifestations and subclinical nature in many herds, the significance of the disease has not been understood until recently, when diagnostic methods improved.

Currently, BVD virus infection is considered to be widespread in the UK cattle herds, causing significant financial losses to affected farms during an outbreak (Pritchard et al., 1989). Paton et al. (1999) report that 95% of 1071 dairy herds in England and Wales were positive for BVD virus antibodies in bulk milk, with 65% of the herds likely to have suffered an outbreak in the recent past and currently having persistently infected animals in the herd.

Apart from causing an outbreak of acute diarrhoea at the time of introduction into a herd, the following short- and long-term effects are caused by a herd infection: infertility, embryonic death, foetal mummification, abortion, congenitally damaged calves and persistently infected (PI) calves that are likely to die of mucosal disease before two years of age. BVD virus has also been identified as an immunosuppressive agent, increasing the risk of infections such as respiratory disease in calves, salmonellosis, interdigital dermatitis and mastitis (Pollreiz al., 1996; Penny et al., 1996; Waage, 2000).

To be able to understand the epidemiology of BVD infection in a herd it is important to know how the virus affects the host at different stages of life:

• Adult, non-pregnant cows: acute diarrhoea or no clinical signs;
• Adult, pregnant cows, first 3 months of gestation: acute diarrhoea or no clinical signs, foetal loss, abortion, congenital defects in calf or PI calf;
• Adult, pregnant cows, mid-gestation: acute diarrhoea or no clinical signs, foetal loss or congenital damage to calf or no effects;
• Adult, pregnant cow, last three months of pregnancy: acute diarrhoea or no clinical signs, calf born with antibodies against BVD;
• Calves that have not been exposed in uterus: acute diarrhoea or mixed respiratory infections, possibly due to immunosupressive effect of BVD;
• PI animals: mixed infections, mucosal disease (usually lethal).