Evaluating food safety risk of Toxoplasma gondii in meat products consumed in the United States
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Toxoplasma gondii is one of the leading foodborne pathogens in the United States. The main modes of T. gondii transmission are ingestion of food, soil or water contaminated with oocysts, or eating raw or undercooked meat containing tissue cysts. A substantial portion of human T. gondii infections is acquired through consumption of meats. The overall goal of this dissertation was to collect and summarize current knowledge and information of T. gondii infection, and estimate the risk of human T. gondii infection due to consumption of meat products that are potentially infected with T. gondii in the United States. A resource document was developed to collect relevant data of T. gondii prevalence in meat animals worldwide, and to identify risk factors associated with T. gondii prevalence. Furthermore, a quality-effects systematic meta-analysis was conducted to estimate T. gondii prevalence in meat animals raised in the United States. These results were used to define the risk level of meat category in a farm-to-retail qualitative assessment. Effects of meat processing on the survival of T. gondii were assessed, and critical steps for inactivating T. gondii were identified. An exponential and a beta-Poisson dose-response models were developed to estimate human infection by using scaling factors. Mouse-derived models were validated against data for the dose-infection relationship in rats. Two risk models were developed to quantitatively predict the risk of T. gondii infection in the United States due to consumption of fresh pork and domestically-produced lamb, respectively. The mean probability of infection per serving of fresh pork ranges from 3.2×10^-7 to 9.5×10^-6, corresponding to 94,606 and 957 new infections annually in the U.S. population and the pregnant women, respectively. The sensitivity analysis suggested that cooking is the most important parameter impacting human health risk. The mean probability of infection of lamb was estimated to be 1.5 cases per 100,000 servings, corresponding to approximately 6,300 new infections per year in the U.S. population. This project systematically evaluated food safety risk of T. gondii through meat consumption, and provided scientific evidence for risk managers that attention to T. gondii infection through meatborne routes is warranted.