EPIDEMIOLOGIC CHARACTERISTICS OF AN OUTBREAK OF CLASSICAL SWINE FEVERIN AN AREA OF HIGH PIG DENSITY

The objective of this study was to analyse an outbreak of classical sw ine fever under a policy of non-vaccination, intensive surveillance an d eradication in an area of high pig density. The virus was found in 5 2 herds, where some 90,000 pigs were slaughtered. The clinical signs w ere vague and the reports of suspect herds generally coincided with in creased mortality. The interval between the first occurrence of clinic al signs and the report of a suspect herd was shorter when the disease was first diagnosed in fattening pigs than when it was diagnosed in s ows, boars or suckling piglets. Among fattening pigs, mortality and mo rbidity appeared to increase with age. The proportion of clinically il l animals was positively correlated with the proportion of serological ly positive animals in a pig house during the phase when the disease w as spreading. Fifty-eight per cent of pig houses containing only clini cally healthy but some virologically positive pigs were serologically negative. Antigen detection was therefore critical for early disease d etection. Serology was nevertheless useful to ascertain that swine fev er was not endemic in the area. The secondary cases were concentrated in the close neighbourhood of the herd initially infected.