Variations in egg size of Trichuris trichiura.

In patients infected with Trichuris trichiura, large eggs as well as more typical eggs were frequently found in the feces; these large eggs have been attributed to human infection by T. vulpis. To clarify whether the female worms laying the large eggs were T. trichiura or T. vulpis, we examined the morphology of adult worms and the size of whipworm eggs obtained from a patient and from several domestic dogs. Adult female T. trichiura worms were easily and quickly distinguished from those of T. vulpis by their convoluted vaginal tracts and uteri. Eggs obtained from the uteri of T. trichiura were of two sizes, with approximately 80% being of the smaller variety (57 X 26 microns) and 20%, the larger (78 X 30 microns). These percentages were about equal to those found the feces of the patient. T. vulpis uterine eggs were slightly larger (82 X 39 microns) than the large eggs of T. trichiura. The distribution of the 2 populations of eggs in 30 adult female T. trichiura was as follows: 1 worm had only large eggs, 14 had only the typical smaller eggs, and 15 had both varieties in their uteri.