Variation in the size and position of Hymenolepis diminuta (Cestoda: Cyclophyllidea) within the rat intestine

Abstract

Data on the dry weight of 410 worms from both male and female rats is shown not to differ significantly from the normal (Gaussian) frequency distribution. This finding justified the use of statistics based on this function.Host body weight is shown to have a highly significant (P < 0.01) effect upon worm dry weight. The heavier the rat, the smaller the worms. An experimental design taking rat body weight into consideration is shown to be up to 36% more efficient in demonstrating differences between groups than one that ignores this source of variation. The point of scolex attachment behind the pyloric sphincter also has a significant effect (P < 0.05) upon worm dry weight. The nearer the scolex is to the stomach, the smaller the worm.The distribution of worm biomass in the intestine does not follow a normal (Gaussian) frequency, but is both asymmetrical (P < 0.001) and flattened (P < 0.001). Over 50% of the parasite biomass lies within the second quarter of the intestine. The distribution of the median points of worm strobilae in the rat intestine is also asymmetrical (P < 0.01) with a peak in the zone which represents a distance of 30–35% from the stomach.The migration of H. diminuta within the rat intestine results in the greater part of the parasite body lying in the second quarter of the intestine. The median points of the strobilae are concentrated at the junction of the first and second quarters of the intestine. This region of the rat intestine appears to offer the optimum site for the growth of H. diminuta.