Animal disease traceability: evaluation of simulated foot-and-mouth disease outbreak metrics with implementation of improved contact tracing of cattle.

INTRODUCTION: In the event of a Foot-and-Mouth Disease (FMD) introduction in the United States (US) animal health officials will need to rapidly trace infected animals and their contacts. Electronic identification (EID) and digital tracing of cattle could improve the speed and accuracy of tracing efforts. This study evaluated the impacts of improving cattle traceability during an FMD outbreak in the US.

METHODS: InterSpread Plus (ISP) was used to simulate FMD outbreaks with a US national livestock population file and animal movement parameters. Scenarios were defined by starting location (California, Nebraska, Texas, New Mexico, New York, and Tennessee), farm type (dairy, feedlot, stocker, cow calf), detection day (8, 14, or 21), and tracing level. The tracing levels represented the current speed and accuracy in the US, a partial EID tracing or an ideal EID tracing implementation. A secondary objective investigated decreasing the geographical size of control areas and surveillance zones under the ideal tracing level. We assessed outcome metrics (infected premises (IPs), outbreak duration, and number of farms under surveillance or in control areas) using a calculation of difference between scenarios and bootstrap confidence interval estimation.

RESULTS AND DISCUSSION: Improved tracing showed the largest potential for decreasing outbreak size when the outbreaks were detected on day 21. The distribution of IPs decreased consistently at the median and beyond with some scenarios showing decreases as low as the 10th percentile. Similar trends were seen in the duration of outbreaks and number of farms in surveillance zones. When the size of control areas and surveillance zones decreased, the number of IPs tended to increase while the number of farms under surveillance decreased in some scenarios and increased in others. Our results support the value of improved cattle traceability that is rapid and accurate for decreasing the risk of large FMD outbreaks in the US. An improved traceability system could also decrease demands for human labor to conduct traces and surveillance during the outbreak, and improve business continuity of producers during and outbreak. More research into the economic trade-offs and EID feasibility are needed to determine the best implementation of EID tracing systems.