Incidence, epidemiology and control of bovine pestivirus infections and disease in Australia and New Zealand.

Pestivirus infection of cattle is widespread and common in both Australia and New Zealand. The majority of adult animals, of the order of 60%, carry antibody. Associated disease is almost entirely that resulting from infection in utero. This includes death of the conceptus, at any stage from conception through pregnancy, or, in those which are born as persistently infected carriers, mucosal disease, most commonly in a chronic form. Little or no disease is recognised as a result of the post-natal infection of non-pregnant animals and these appear to be of little consequence as spreaders of infection. Transmission and enzootic maintenance depend primarily on the persistently infected carriers that are immunotolerant after early in utero infection and range clinically from normal, or nearly normal, to overtly mucosal diseased. The expulsion of an infected conceptus, and associated discharges, also provides an effective source of infection. There is generally little active control attempted. Vaccines are not available in Australia and are not widely used in New Zealand. However, interest in control is growing in those areas of the industry, especially in breeding by artificial insemination and embryo transfer, where it is perceived that the pathogenic impact of the virus may be amplified.