Immunological responses to bovine virus diarrhoea virus infections.

Infection of normal calves with bovine virus diarrhoea virus (BVDV) is a transient self-limiting infection that can result in a period of immunosuppression. The virus appears to be able to replicate in all of the major lymphocyte sub-populations as well as in accessory cells. This may result in the leukopenia that is often a sequel of infection and affects B-cells as well as the T-cell sub-populations expressing either BoCD4 or BoCD8 antigens. B and T-cell responses are affected as a consequence of exposure to BVDV and there is a reduced ability to control other infections. Evidence is summarised and shows that immunoglobulin is an important mediator of immunity to infection with BVDV. Although the foetus can mount an immune response in the latter part of gestation, during the first trimester it does not. A specific state of tolerance is induced and this is associated with change in the proportion of certain lymphocyte sub-populations and ability to respond to immune stimulation.