Thermal death curves have also been developed to establish the effect of cold treatment on the viability of T. gondii in meat, Drs. Hill and Gamble continue. “Although tissue cysts remain viable at temperatures slightly below freezing, 11.2 days at 20 degrees Fahrenheit and 25 days at 30 degrees Fahrenheit, parasites are inactivated almost instantaneously at temperatures of 15 degrees F. and lower,” they say.
According to Drs. Hill and Gamble, scientific knowledge of the effect of various curing processes on T. gondii is limited; currently no ready-to-eat meat preparation process for salami, pepperoni, dry-cured ham, summer sausage, etc. exists that can be correlated with inactivation of T. gondii.
Recent studies in Dr. Hill’s lab tested the effect of five variables, salt/brine concentration, water activity, pH, temperature, and time on inactivation of T. gondii bradyzoites in pork during preparation of dry-cured pork sausage. “Results indicated that encysted T. gondii bradyzoites do not survive the early stages of the dry curing process, resulting in rapid inactivation of bradyzoites, rendering these products safe from risk with respect to T. gondii transmission to human consumers,” Dr. Hill reports. “Previous studies have shown that pumping of pork products with salt solutions containing 2 percent sodium chloride, or greater than or equal to 1.4 percent potassium or sodium lactate, has been shown to inactivate T. gondii tissue cysts in pork.”
T. gondii tissue cysts were rendered non-infectious by treatment with 40 to 50 krad of cesium-137, indicating that irradiation is a suitable method for eliminating the risk of this parasite in meat and meat products, they add.
The USDA advises that consumers cook any meat or poultry product to an internal temperature of 145 degrees Fahrenheit, followed by a 3-minute rest, which is effective for killing T. gondii.
“While meat products have been identified as an important source of T. gondii infections in humans, overall, the prevalence of viable T. gondii in U.S. retail meat, including beef, pork, and chicken, is very low, according to research,” Drs. Hill and Gamble emphasize.
Drs. Hill and Gamble concur that, despite the widespread distribution of T. gondii in wildlife and the opportunity for cats to contaminate the environment with the resistant oocyst stage, it is possible to raise pigs free from T. gondii infection, as evidenced by many negative pork production sites found in recent prevalence studies. “Prevention of infection in pigs is accomplished through good production practices on the farm, which include: 1) adopting an effective rodent control program to minimize mouse and rat populations, 2) creating a level of biosecurity which reduces or eliminates exposure of pigs to wildlife, 3) eliminating feral cats and securing feed and pork production areas from access by cats, 4) prompt removal of dead pigs, and 5) changing or thoroughly washing boots before entering barns to avoid tracking in oocysts,” they recommend.
Toxoplasma’s Impacts on Human Behavior
If you’re feeling more entrepreneurial than usual, or more interested in pursuing business-related activities or studies, you may be infected with Toxoplasma gondii (T. gondii).
Implausible as this may seem, a recent study conducted by researchers at the University of Colorado (CU), Boulder demonstrates that T. gondii-positive individuals are more likely to major in business and more likely to pursue a management and entrepreneurship emphasis than those not infected with the organism, according to Stefanie Johnson, PhD, associate professor of management in the CU Leeds School of Business, the lead author of the study.
Dr. Johnson and her colleagues point out that the pesky protozoan parasite that infects an estimated 2 billion people worldwide has been linked to behavioral alterations in humans, as well as other vertebrates. Studies have linked suicide and schizophrenia to Toxoplasma infection, for example.