Several recent studies assessed the risk associated with consuming meat products potentially infected with T. gondii, according to Abani Pradhan, PhD, an associate professor in the Department of Nutrition and Food Science (NFSC) and the Center for Food Safety and Security Systems, and also the director of the NFSC graduate program at the University of Maryland, College Park.
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“We have summarized a recent 10 years of prevalence of T. gondii in conventional and organic meat animals and meat products, and identified risk factors for animal infection at the farm level,” Dr. Pradhan says. “This serves as a useful resource and information repository for informing quantitative risk assessment studies for T. gondii infection in humans through meat consumption.”
Additionally, Dr. Pradhan and his collaborators performed a systematic quality-effects meta-analysis to provide a quantitative estimate of T. gondii prevalence in meat animals. This included confinement raised market pigs, confinement raised sows, non-confinement raised pigs, lamb, goats, and non-confinement raised chickens in the U.S. A meta-analysis is a statistical analysis that combines the results of multiple scientific studies.
T. gondii prevalence in non-confinement raised pigs ranked the highest (31.0 percent), followed by goats (30.7 percent), non-confinement raised chickens (24.1 percent), lambs (22.0 percent), confinement raised sows (16.5 percent), and confinement raised market pigs (5.6 percent).
“These results indicate that T. gondii-infected animals are a food safety concern,” Dr. Pradhan explains. “The computed prevalence can be used as an important input in quantitative microbial risk assessment models to further predict public health burden.”
Dr. Pradhan and his team also evaluated the effects of meat processing on the survival of T. gondii. “The critical steps for inactivating T. gondii tissue cysts along the meat production-to-consumption chain were identified through a qualitative farm-to-retail exposure assessment framework,” he relates. “We then developed dose-response models to predict T. gondii infection in humans from ingestion of T. gondii-infected meats. A dose-response model establishes the relationship between the magnitude of exposure to the hazard and the probability of occurrence of an adverse health effect.”
These researchers performed two farm-to-table quantitative microbial risk assessment (QMRA) studies to quantify the public health burden associated with consumption of fresh pork and domestically produced lamb in the U.S.
“In the context of available data, based on the sensitivity analysis, we identified cooking as the most effective method to influence human health risk,” Dr. Pradhan points out. “The QMRAs provide a scientific basis for risk management and could also serve as baseline models to quantify infection risk from T. gondii and other parasites associated with meat products.”
Pharmaceuticals in Progress
There are promising new drug candidates in the pipeline to treat T. gondii infections in both animals and humans, according to Wes Van Voorhis, MD, PhD, a professor of allergy and infectious diseases and director of the Center for Emerging and Re-emerging Infectious Diseases at the University of Washington (UW), Seattle.
“One exciting new drug targets a protein kinase in T. gondii that has been shown as essential for host cell entry and intracellular growth,” Dr. Van Voorhis says. “The target is calcium-dependent protein kinase 1, that appears to have moved from the plant world to the T. gondii genome. There is no mammalian equivalent, so targeting it does not harm human cells.”
The Van Voorhis laboratory at UW, along with UW chemists Dustin Maly, PhD, and Erkang Fan, PhD; and researchers J. Stone Doggett, MD, at Oregon Health and Science University, Portland; Luis Ortega Mora, DVM, PhD, at Complutense University in Madrid, Spain; and Andrew Hemphill, PhD, at the University of Berne, Switzerland have worked together to perfect this drug in animal models, Dr. Van Voorhis reports, noting that the drug is in pill form.
“We now have a late pre-clinical candidate that is effective against T. gondii in vitro and in mouse and pregnant sheep models of T. gondii infection, protecting both mothers and lambs,” he relates. “This drug is safe in juvenile and adult animals, as well as pregnant animals, and is ready for final safety testing and submission to the FDA for first testing in humans. The drug shows activity in the brain against the latent, bradyzoite form of toxoplasmosis, bringing hope to the idea that treatment with this drug can arrest and eliminate brain infection, even in the latent form.”