RATE OF SUCCESSFUL PSEUDORABIES VIRUS INTRODUCTIONS IN SWINE BREEDINGHERDS IN THE SOUTHERN NETHERLANDS THAT PARTICIPATED IN AN AREA-WIDE VACCINATION PROGRAM

In this study we estimated the rate of successful pseudorabies virus ( PRV) introductions in PRV-free and PRV-low (5.1% +/- 4.4%) seroprevale nce breeding herds that participated in an area-wide vaccination progr amme. During a 3 year period, all breeding pigs in 99 herds were teste d for antibodies against PRV (whole herd testing) at least twice. To d etermine if seroconversions to PRV had occurred in these herds, the se rological data of each whole herd testing were compared with the subse quent whole herd testing, In all, 259 pairs of two successive whole he rd testings were available. In 52 of these pairs, one or more seroconv ersions to PRV were observed among the breeding pigs, indicating succe ssful PRV introduction. There was no apparent indication that these in troductions originated from latently infected pigs in the herds, becau se herd serostatus (PRV seropositive breeding pigs present or not pres ent) and culling policy (all or not all PRV seropositive pigs culled b etween two successive sample collections) were not associated with the occurrence of seroconversions. Absence of sanitary facilities at the entrance of the farm and the use of homebred gilts (in comparison with the purchase of PRV-free stock) were associated with a significantly (P less than or equal to 0.01) higher rate of successful PRV introduct ion. The rate of successful PRV introduction significantly (P < 0.01) decreased with time since the start of the study.