Eradication of pseudorabies virus from three large swine herds achieved by management intervention and use of a vaccine with a deletion for glycoprotein I.

Three large farrow-to-finish swine herds in Illinois, quarantined because of infection with pseudorabies virus (PRV), were enrolled in an intensified PRV eradication program, with the goal being release from quarantine within 3 years. The intervention plan primarily relied on vaccination, using a vaccine with a deletion of the genes coding for glycoprotein I, in breeding and growing/finishing pigs and decreases of movement and mixing of growing/finishing pigs. The initial goal was to decrease viral spread in the growing/finishing pigs, thereby enabling production of seronegative replacement gilts. Off-site rearing of replacement gilts was implemented in 1 recently infected herd in which the seroprevalence in the growing/finishing group was high. Results of bimonthly serologic monitoring indicated that there was minimal spread of PRV in the growing/finishing pigs after 1 year. Increases in the number of sows culled combined with an increase in the number of seronegative replacement gilts entering the breeding group resulted in a reduction of sow seroprevalence, so that phased test and removal of seropositive breeding stock could commence in all 3 herds at about 18 months after initiation of the program. Persistent use of the test-and-removal procedure and repeated testing for release from quarantine were required for the most recently infected herd. All herds were released from quarantine within 3 years, indicating that a PRV eradication program based on vaccination and management changes designed to minimize the spread of PRV can be used in conjunction with test-and-removal procedures to effectively eliminate PRV from large farrow-to-finish swine herds.