Modeling the impact of control zone restrictions on pig placement in simulated African swine fever in the United States

TL;DR

This study models the effects of control zone restrictions on pig placement during simulated African swine fever outbreaks in the U.S., revealing how zone size and duration influence unplaced pigs, depopulation, and economic losses.

Contribution

It provides a novel simulation-based analysis of control zone strategies' impacts on pig placement and economic outcomes during ASF outbreaks in the U.S.

Findings

Shorter control zones reduce unplaced pigs by up to 33%.

Expanding infected zones increases unplaced pigs significantly.

Economic losses can exceed $800 million depending on culling scenarios.

Abstract

African swine fever (ASF) is a highly contagious viral disease that poses a significant threat to the swine industry, requiring stringent control measures, including movement restrictions that delay pig placements, impacting business continuity. The number and economic impact of unplaced healthy animals due to control zone restrictions remains unmeasured. This study evaluates the economic and epidemiological impacts of control zone placement restrictions during simulated ASF outbreaks in U.S. commercial swine farms. We model the spread of ASF and apply the U.S. National Response Plan (NRP) alongside alternative mitigation strategies, analyzing key metrics such as the number of unplaced pigs, depopulated pigs, infected farms, and total economic losses. Our findings estimate the median number of unplaced pigs in the first year was 153,020 (IQR 27,377 to 1,307,899) under the NRP scenario. Shorter control zone durations (20 to 25 days) effectively reduce the median number of unplaced pigs by 16.7% to 33.5%, whereas longer durations (40 days) increase unplacement numbers by 32%. The median number of depopulated pigs remains broadly consistent across all durations. Expanding the infected zone (5 to 15 km) increases the median number of unplaced pigs by 53.6% to 282% while reducing depopulated pigs by 28.8% to 73.9%, respectively. Economic losses are estimated through a model that includes depopulated and unplaced animals requiring culling. We examined the situations when 5%, 12%, or 20% of unplaced pigs required culling and found that the total cost ranged from zero (no second infection) to over $800 million.