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A Comparison of Three Strains of Trichinella Spiralis

II. Longevity and Sex Ratio of Adults in the Intestine and Rapidity of Larval Development in the Musculature¹

1. Little or no difference was found among the three strains of T. spiralis in regard to longevity and sex ratio of the adults and the rapidity of larval development.

2. Animals infected with small doses of T. spiralis showed considerable variations in the average proportions of larvae recovered to larvae fed. The results were much more consistent when the doses bordered on the lethal.

3. There was greater regularity in the longevity of T. spiralis adults in the intestines of mice infected with doses bordering on the lethal as compared with those lightly infected. After the first two weeks, the adults in the intestines of mice were lost rapidly. The worms appeared to withstand the effects of the host in the large intestine better than in the small intestine, as indicated by the exclusion of adults from the latter site usually after the first month. Adults were not observed later than 54 days after infection.

4. There was considerable regularity in the course of the sex ratios. In animals possessing a reasonable number of adults, the ratios remained invariably in favor of the females until the 16th or 18th day but then became reversed in favor of the males. In only one animal infected with 10 larvae per gram of body weight was the sex ratio in favor of the females on the 20th day. The reversal in many cases was so complete that males were found to the exclusion of females. These results are contrary to the generally accepted view that the males are lost soon after the females are fertilized.

¹ Read at the 38th Annual Meeting of the American Society of Tropical Medicine, Richmond, Va., 1942.