Serologic status of pseudorabies virus in growing-finishing pigs in quarantined herds

It has been reported that pseudorabies virus (PRV) stops spreading within growing-finishing sections of a large percentage of infected farrow-to-finish herds. This study was designed to follow the PRV status of growing-finishing pigs in a sample of infected herds. Fifteen infected herds were selected, of which 11 had seropositive finishing pigs and 4 had seronegative finishing pigs. These herds were visited quarterly for one year, and a cross section of growing-finishing pigs was tested for the presence of anti-PRV antibodies. The 4 herds that initially were seronegative remained seronegative, whereas of the 11 herds initially seropositive, 4 remained seropositive, 4 became seronegative, and 3 became temporarily seronegative before becoming seropositive again. Three characteristics serologic profiles were observed: one indicating continued viral spread; one indicating no spread for at least the preceding 3 months; and one indicating that PRV spread had recently ceased in this section of the herd. Results of our study indicated that periodic monitoring of a cross section of the growing-finishing pigs for their PRV serologic status was valuable for determining whether PRV was actively spreading in this section of the herd.