Identifying control strategies to eliminate African swine fever from the United States swine industry in under 12 months

With the rising risk of African swine fever (ASF) introduction into the U.S., there is substantial emphasis on preparation for an epidemic to mitigate the economic and societal impacts. Mathematical models represent a vital tool for simulating future epidemics and examining the effectiveness of response strategies. This study expands on our spatially explicit stochastic compartmental farm-level transmission model, PigSpread-ASF, to identify the control strategies necessary to eliminate ASF from domestic swine populations in three, six, nine, and twelve months. We achieved this by incrementally increasing the intensity of the control actions detailed in the USDA national response plan, which consists of i) quarantine and depopulation of detected farms; ii) a 72 hour movement standstill; iii) contact tracing with subsequent diagnostic testing; and iv) the implementation of control areas (infected and buffer zone) and surveillance zones (including routine diagnostic testing, pre permit testing and movement restrictions). For this model, ASF was deemed eliminated after three consecutive months of no new ASF cases following each time period, as determined by WOAH. Our results indicate that the current national response plan would need to i) increase radii and duration of control areas and surveillance zones, ii) extend the traceback and quarantine for contact farms; iii) extend the movement standstill; iv) prohibit repopulation of depopulated farms; and v) quicker baseline detection of ASF, at varying intensities, to eliminate ASF within three, six, nine and twelve months. The elimination of ASF in 12-months required extension of the buffer zone radius to 5 km and maintenance of the control areas and surveillance zones for 60 days, a traceback and quarantine of 60 and 30 days for the contact tracing, and a standstill of 30 days. In contrast, the three-month scenario required extension of the infected zone, buffer zone and surveillance zone radii to 20 km each and maintenance of the control area and surveillance zones for 90 days, a traceback and quarantine of 90 days for contact tracing, and a standstill of 90 days. By intensifying the current national response plan, ASF would likely be eliminated within 12-months of its introduction. However, it is pertinent to consider the limitations posed by resource capacities and the impact that intensifying control may have on business continuity. Nevertheless, our study provides beneficial guidance to aid preparation for a future ASF introduction and estimates the infrastructure and personnel required to bring an epidemic under control promptly.