Submitted to: Journal of Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 14, 1997
Publication Date: N/A
Interpretive Summary: Infections by the single-celled parasite, Toxoplasma gondii, are widespread in humans and livestock. Humans become infected with T. gondii by ingesting food or water contaminated with the resistant stage (oocysts) from infected cat feces or by ingesting tissue cysts from infected meat. Oocysts of T. gondii are highly resistant to environmental influences and can survive for months in the environment. Compared with oocysts, tissue cysts are not resistant to environmental influences. Toxoplasma gondii tissue cysts are killed by cooking and freezing, and they are killed instantly at 66 C and -12 C. However, little is known of the effect of different salting procedures on the viability of T. gondii tissue cysts in prepared, uncooked, and processed meats. A scientist at the Beltsville Agricultural Research Center has determined that Toxoplasma parasites in meat are killed by the concentrations of salts used in commercial curing processes. These results will be useful to public health workers, veterinarians and parasitologists.
The effect of storage of Toxoplasma gondii tissue cysts in various NaCl solutions at different temperatures was studied. Tissue cysts from rodent brains were suspended in 0.85%, 2.0%, 3.3%, and 6.0% aqueous NaCl solutions. After storage at 4 to 20 C for various time intervals, brains were bioassayed in mice for viability of T. gondii. At 4 C, tissue cysts survived for at least 56 days in 0.85% NaCl, for 49 days in 2.0% NaCl, and for 21 days in 3.3% NaCl solutions. At 10 C, tissue cysts survived for at least 21 days in 0.85%, 2.0%, and 3.3% NaCl solutions. At 15 C, tissue cysts survived for at least 21 days in 0.85% NaCl, 14 days in 2.0%, and 3.3% NaCl solutions. At 20 C, tissue cysts survived for 14 days in 0.85% NaCl, 7 days in 2.0% NaCl, and 3 days in 3.3% NaCl solutions. Tissue cysts generally did not survive in 6.0% NaCl solution at any temperature.