Morphologic criteria for distinguishing the sex of Trichinella spiralis larvae from muscle.

The results of this study revealed two principal features that permit one to distinguish male from muscle Trichinella spiralis with ease and accuracy: (1) position of intestine, or hindgut, in relation to gonads, and (2) number of stichocytes in cell body. In male, intestine, near middle of testis on ventral side of body, passes diagonally to dorsal side, and joins cloaca at distal end of body. In female, intestine, below esophago-intestinal junction, lies along dorsal aspect of body, parallels ovary, and then joins cloaca at distal end of body. The number of stichocytes in ranged from 47 to 52, with a mean of 49; whereas number in ranged from 37 to 45, with a mean of 43. The number of stichocytes as a means of distinguishing from is reported for first time. Since sex of muscle trichinae, in contrast to that of intestinal trichinae, is not easily determined, a study was made to determine features of muscle trichinae that will enable sexes to be distinguished accurately and readily. A preliminary report of this study appeared in abstract form (Villella, 1963). According to Hemmert-Halswick and Bugge (1934), many textbooks carry an illustration by Leuckart, of a well-developed male muscle which actually exhibits characteristic features of a muscle trichina, and in an early picture, Pagenstecher designated as female muscle trichina one that has characteristics of a male muscle trichina. The same authors listed several anatomic criteria for distinguishing from relating chiefly to shape and size of gonads, and position of midgut and hindgut. Roth (1943), who, in immunologic experiments, infected animals with larvae that were all of same sex, stated that the separating of two sexes from each other to provide infection doses of one sex alone was rather difficult and tedious . . . and in spite of exercise of great care in isolating male and larvae from each other, occasional confusion of with could not be avoided. Microscopically, it has been difficult to decide whether a muscle larva is male or female, Received for publication 20 May 1966. * Part of this study was conducted at The University of Michigan. t The Puerto Rico Nuclear Center is operated by University of Puerto Rico for U. S. Atomic Energy Commission (Contract AT-(401)-1833). since gonads of both sexes are similar in their overall appearance and size. MATERIALS AND METHODS Muscle trichinae were obtained from rats according to standard procedures described by Gould (1945). Each of several hundred clean larvae was examined at a magnification of 430 X with a compound microscope. Three lots of trichinae were selected and labeled males, females, and males and females. In order to test reliability of morphologic criteria of sex of muscle trichinae, 100 larvae from each lot were inoculated by stomach tube into each of six trichina-free Swiss mice. Mice inoculated with lot of trichinae labeled males and females served as controls. Approximately 35 days later all of mice were killed, their skeletal muscles processed by standard pepsin-hydrochloric acid digestion method, and larval counts were made. Both live and fixed larvae were examined, gonadal structures were measured with aid of a compound microscope fitted with an ocular micrometer. Distinguishing features were illustrated in a composite drawing made from examination of several live, as well as fixed, male and larvae. RESULTS AND DISCUSSION In present study, two principal features pe mitted one to distinguish from with ease and accuracy: (1) position of intestine in relation to gonads, and (2) number of stichocytes in cell body (or Zellenkorper). Figures 1 and 2 illustrate specific features of muscle trichinae. In male (Fig. 1), intestine, near middle of testis on ventral side of body, passes diagonally to dorsal side, and joins cloaca at distal end of body. In (Fig. 2), intestine, below esophago-intestinal junction, lies along