Quantifying Human Health Risks Caused by Toxoplasmosis from Open System Production of Swine

Open livestock production systems, including free-range and organic livestock systems, seek to improve the welfare of animals by letting them roam in unconfined spaces. This increases their exposure to potentially harmful micro-organisms. For example, swine in open production systems have a much greater risk of Toxoplasma gondii infection. When transmitted through the food chain, T. gondii threatens human health, especially in unborn children of women infected during pregnancy, as well as the lives of patients with compromised immune systems. By contrast, conventional total confinement production systems can now keep this human health risk at or near zero. This article describes a probabilistic risk simulation model that quantified the tradeoff between greater use of open swine production systems and increased cases of toxoplasmosis in humans. The model predicts that every 1804 pigs shifted from conventional total confinement to open production (95% confidence interval 747-9520) would cause the loss of one additional human quality-adjusted life year (QALY), and that increasing the fraction of U.S. swine raised in open/free range operations by 0.1% (approx. 65,000 pigs) would cause a loss of approximately 36 human QALYs per year, including between 1 and 2 extra adult deaths per year.