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Bovine virus diarrhoea virus is closely related to the viruses that cause classical swine fever in pigs and border disease in sheep.

This virus causes a complex of diseases in cattle the most important of which interfere with reproduction, affect the foetus and lead to mucosal disease.

BVD virus can also cause enteritis during acute or transient infection which is usually mild but occasionally severe enough to kill even adult cows. Transient BVD virus infection is also believed to cause significant suppression of disease resistance and may contribute to the pneumonia complex in calves.

Infection immediately before or during the breeding season will reduce conception rates and cause early death of the embryo. Infection at any stage of pregnancy can result in abortion.

The virus can also cause deformities in the calf. However of particular importance is infection in the first third of pregnancy when developing calves that survive remain Persistently Infected with the virus (PI calves) and it is these calves, once born, that provide the major route of spread for this virus.

They often appear normal but always shed virus throughout their lives. Many develop a fatal enteritis known as mucosal disease before they reach maturity, however, significant numbers of PIs survive well into adulthood. Semen from transiently infected bulls can also spread infection.Theoretically other ruminant species, such as sheep and deer, can be a source of infection for cattle although sheep are at greater risk from cattle than vice versa.

Contaminated needles and other equipment can also spread virus from animal to animal and herd to herd. Therefore careful herd health security and quarantine are an essential part of control. The economic losses for an uncontrolled outbreak of BVD can be very great.

It has been calculated that in a large beef herd these can exceed £45,000 over a ten year period while losses can be greater in the dairy herd. In most outbreaks reproductive losses are the most significant although mucosal disease cases are the most obvious.

Where possible control by identification and removal of PI animals is advised with subsequent exclusion of any potential sources of reinfection. Screening is by ELISA test for antibody on blood or bulk milk with secondary screening of animals with low or negative antibody for virus, also using ELISA tests.

In some herds where potential sources of reinfection cannot be excluded vaccination might be the only viable option although this is likely to be expensive and protection of the herd may be incomplete.

Vaccination may also be used in the course of an eradication programme, particularly in beef herds.