The Thermal Death Point of Cysticerci of Taenia saginata

Abstract

Although it has long been recognized that thorough cooking of beef will destroy contained cysticerci of Taenia saginata, the larval stage of the common tapeworm of man, opinions of investigators concerning exact temperatures that are lethal to this parasite are somewhat varied. For example, Lewis (1872) heated fresh water, in salty water, and in a dry state encapsulated cysticerci to which a small amount of meat was left attached, and reported that death of the parasite, as evidenced by lack of movement, resulted when the organisms were exposed to a temperature of 54.40 C, for 5 minutes. Pellizzari et al (1874) reported that cysticerci die when heated to 600 C. Perroncito (1877) exposed decapsulated cysticerci to various temperatures and reported, mainly on the basis of the appearance of the parasites and whether or not movement could be induced, that they sometimes die at 440 C, often at 450 C, and never survive exposure to a temperature of 46' C. In some cases the cysticerci, after subjection to heat, were swallowed by human subjects to ascertain whether the parasites were alive. Ostertag (1913) stated that cysticerci will not survive temperatures of 450 to 500 C. Stiles (1898) reported that according to Hertwig a temperature of 520 C reduces the parasites to a smeary, soft condition. Clarenburg (1931) immersed pieces of muscle tissue, about 8 cm thick, containing cysticerci in boiling water for periods of 5, 10, 15, 20, 30, and 50 minutes and used the ability of the cysticerci to evaginate in vitro as a criterion of life. While evagination did occur in those heated 10 minutes or less, those heated for longer periods failed to evaginate, and were, therefore, considered dead. The internal temperatures of the pieces of meat in which the cysticerci were killed varied from 710 to 910 C. The internal temperatures of those pieces in which the cysticerci were not killed were not specified. To obtain specific information on the exact temperatures at which cysticerci of Taenia saginata die, a series of tests was carried out in which (a) decapsulated cysticerci, and (b) small pieces of flesh containing the encapsulated parasites, were heated to various temperatures in physiologic saline or Ringer's solution and the viability of the parasites tested (1) by exposure to warm solutions of sodium taurocholate (sodium salt of a bile acid, taurocholic acid), to induce movement and/or evagination, (2) by observance of flame cells for evidence of activity in those cysticerci that failed to exhibit movement or that failed to evaginate in the warm sodium taurocholate solution, or (3) by passage through the digestive tract of a human subject.