Probability of exporting infected carcasses from vaccinated pigs following a foot-and-mouth disease epidemic

Emergency vaccination is an effective control strategy for foot-and-mouth disease (FMD) epidemics in densely populated livestock areas, but results in a six-month waiting period before exports can be resumed, incurring severe economic consequences for pig exporting countries. In the European Union, a one-month waiting period has been discussed based on negative test results in a final screening. The objective of this study was to analyze the risk of exporting FMD-infected pig carcasses from a vaccinated area: (1) directly after final screening and (2) after a six-month waiting period. A risk model has been developed to estimate the probability that a processed carcass was derived from an FMD-infected pig (Pcarc). Key variables were herd prevalence (PH), within-herd prevalence (PA), and the probability of detection at slaughter (PSL). PH and PA were estimated using Bayesian inference under the assumption that, despite all negative test results, =1 infected pigs were present. Model calculations indicated that Pcarc was on average 2.0 × 10-5 directly after final screening, and 1.7 × 10-5 after a six-month waiting period. Therefore, the additional waiting time did not substantially reduce Pcarc. The estimated values were worst-case scenarios because only viraemic pigs pose a risk for disease transmission, while seropositive pigs do not. The risk of exporting FMD via pig carcasses from a vaccinated area can further be reduced by heat treatment of pork and/or by excluding high-risk pork products from export.