Herd factors affecting the selection and success of intervention strategies in the program for eradication of pseudorabies (Aujeszky's disease) virus from Illinois swine farms.

The program for eradication of pseudorabies virus (PrV) from swine herds in Illinois was evaluated with respect to compliance with Livestock Conservation Institute (LCI) guidelines for selection of intervention strategies and for the effectiveness of these interventions under different herd conditions. The sample consisted of 395 swine operations quarantined between 1988 and 1994. These herds were followed until the end of 1996. The association of herd characteristics (number of sows, sow PrV seroprevalence, type of housing, number of PrV-seropositive farms within 1.5 mi) at the time of quarantine with the producer's selection of an initial intervention strategy (vaccination, offspring segregation, test-and-removal, depopulation-and-repopulation) was analyzed using logistic multiple regression. The interaction of herd characteristics with intervention strategies to affect the duration of quarantine was analyzed using multivariable Cox regression. Factors favoring selection of vaccination were increased herd size, higher sow PrV seroprevalence, and more PrV-seropositive farms within 1.5 mi. Offspring segregation was preferred when sow PrV seroprevalence was higher, and test-and-removal was preferred when seroprevalence was lower. Depopulation-and-repopulation was more likely in outdoor operations. Except for depopulation-and-repopulation, selection of an intervention strategy was in accordance with LCI guidelines. Vaccination and offspring segregation were associated with longer times under quarantine, and test-and-removal and depopulation-and-repopulation with shorter times. Test-and-removal was more effective in reducing the duration of quarantine when sow PrV seroprevalence was low. Vaccination increased the duration of quarantine less when sow PrV seroprevalence was high. Vaccination increased the duration of quarantine more when there were one or more PrV-seropositive farms within 1.5 mi than when there were no PrV-seropositive farms within 1.5 mi. It is apparent that herd characteristics affect the duration of quarantine and therefore need to be taken into account in the selection of a PrV-intervention strategy.