A retrospective study of factors associated with eliminating circulating pseudorabies virus in sow herds

Objective: To define risk factors associated with sow herds that have not been successful in stopping circulation of pseudorabies virus (PRV, Aujeszky's disease). Methods: Officials in charge of eradicating PRV in the major swine-producing states in the United States completed surveys to compare herds in which virus circulation had been successfully stopped (cases) to those in which it was not (controls) in an unmatched case-control design. Unsuccessful herds were defined as breeding herds that were diagnosed with PRV but that continued to have replacement animals become infected. The diagnostic and vaccination methods, characteristics of the farm and livestock, and eradication methods attempted were investigated. Multiple logistic regression analysis was used to compare and select statistically significant variables. Results: Offsite and all-in-all-out (AIAO) finishing was more frequent among successful than unsuccessful herds. The frequency of other practices, such as sorting back pigs from one AIAO group to another, did not differ between successful and unsuccessful herds. In a higher proportion of successful herds, sows were culled directly from the farrowing room and conversely, a lower proportion of successful herds mixed cull sows with the finishing pigs. Unsuccessful herds were more likely to have other infected herds within 3.2 km (2 miles). Unsuccessful farms were more likely to raise gilts in their own facilities and did not cull out of the farrowing room but instead retained the sows. They also did not regularly clean and disinfect the livestock trucks or use a syringe dedicated to PRV vaccinations. Implications: The picture of the problem herd that develops from this analysis is of a herd that is slow to take up new technologies, particularly biosecurity and disease control technologies.