[Swine fever: a changing clinical picture]

Abstract

Signs of disease typical of classical swine fever are often absent in outbreaks caused by virus strains of low virulence. The clinical picture and epizootiology of these strains causing swine fever in the Netherlands are elucidated on the basis of experimentally induced infections and outbreaks in the field respectively. Strains of both high and low virulence are involved in the present epizootic. The absence of symptoms hampers early detection in the field. Intra-uterine infections may occur in a large proportion of the pregnant sow population. On one farm, 43 per cent of these sows showed intra-uterine infection. Piglets born of these sows may live for weeks and occasionally months without showing any marked symptoms, as a result of which the virus may persist over prolonged periods even in vaccinated herds.