PRRSV Negative Herds: A Survival Analysis

1 Summary and Implications Despite a significant body of research, interventions for PRRSV infection remain elusive. Traditional approaches to managing the risk of diseases have not been successful in many cases of PRRSV infection. While elimination of the virus from farms is possible, it is not without cost and re-infection is common. This survey sought to quantify the expected duration of PRRSV negative status on farms that were repopulated with PRRSV negative animals or had undergone a PRRSV elimination program. Results of 96 cases reveals a range of <1 to 312+ weeks duration of negative status. A survival analysis of 84 farms revealed a probability of surviving with negative status for two full years of 58.3% with a standard error of 11.5%. The probability of survival through 4 years was 42% with a standard error of 16%. A greater percentage of farms that were re-infected shared resources such as equipment, personnel, and/or vehicles with known positive farms. Positive farms also had a relatively shorter average distance to known positive farms than those remaining negative. The results of this study indicate that PRRSV-negative farms are not very likely to remain negative for a long duration given current technologies. Longer survival of negative status appears to be associated with greater distance from known positive farms and stricter biosecur-ity. Sharing of equipment and other resources as well as a closer distance to other farms should be considered risk factors that can lessen the probability of farms maintaining negative status.