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

Abstract

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 impacts observed in previous outbreaks. 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 assess the effectiveness of the National Response Plan (NRP) and identify the control strategies necessary to eliminate ASF from domestic swine populations in the southeast U.S. in three, six, nine, and twelve months. We achieved this by incrementally increasing the intensity of the control actions i) quarantine and depopulation; ii) a 72-hour standstill; iii) contact tracing; and iv) control areas (composed of infected zones (3 km) and buffer zones (2 km) and surveillance zones (5 km), which include 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 demonstrate that under the NRP, only 65.1 % of simulations in our study area were eliminated in a 12-month time frame. Through the analysis of 11 different scenarios, we propose that a future ASF control strategy 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, to eliminate ASF within three, six, nine and twelve months in the study area. The elimination of ASF in 12-months required buffer zone radius of 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 in the southeast U.S. However, it is pertinent to consider the limitations posed by resource capacities and the impact that intensifying control may have on business continuity.