Increased Survival of Swiss Mice Given Sublethal Infections of Trichinella spiralis

Male mice infected with 70, 160, 325, 420, and 535 larvae of T. spiralis lived longer than uninfected controls. Males infected with 35, 650, and 685 larvae had life spans similar to controls. Females infected with 35, 70, 160, 325, and 420 larvae lived longer than their controls, whereas females infected with 535 larvae had a life span similar to the controls. As expected, males and fe- males infected with more than 790 and 650 larvae, respectively, had shorter life spans than their con- trols. Reduced fighting among males, suppression of the development of breast cancers in females, and reduced food intake are proposed as possible explanations for the demonstrated longer life spans of the infected animals. Many studies have shown that mice infected with 30 to 75 larvae of T. spiralis per gram of weight will die within a relatively short period of time (Rappaport and Wells, 1951; Ewert and Olson, 1961; Kozar and Kozar, 1963; and others). To the author's knowledge, how- ever, no one has determined the effects of sublethal levels of infection on the life spans of mice or other animals. The present study shows that sublethal levels, in general, in- creased the life expectancy of Swiss mice.