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 (P-carc). Key variables were herd prevalence (P-H), within-herd prevalence (P-A), and the probability of detection at slaughter (P-SL). P-H and P-A were estimated using Bayesian inference under the assumption that, despite all negative test results, >= 1 infected pigs were present. Model calculations indicated that P-carc was on average 2.0 x 10-5 directly after final screening, and 1.7 x 10-5 after a six-month waiting period. Therefore, the additional waiting time did not substantially reduce P-carc. 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.