Changes in the distribution of Hymenolepis diminuta (Cestoda: Cyclophyllidea) within the rat intestine during prepatent development

Abstract

The changes in the distribution of Hymenolepis diminuta within the rat intestine have been followed over the period 3 to 16 days postinfection using rats, each infected with 10 cysticercoids of H. diminuta, fed ad libitum on Purina Rat Chow.The parameters investigated were distribution of scolex attachment sites in the intestine, and distribution of parasite biomass in the intestine based on strobila length, ex vivo weight distribution, and in vivo weight distribution. Both the scoleces and biomass of 3- and 5-day-old worms are concentrated in the second quarter of the intestine. The mean scolex attachment point for 5-day-old worms was 39% of the total intestinal length behind the pyloric sphincter. Between days 5 and 7 there was a marked anterior migration of the young worms, so that at 7 days the mean scolex attachment site was 15% of the total intestinal length behind the stomach. Over the same period of time the mean in vivo weight distribution moved forward from a point 44% behind the pyloric sphincter to one only 23% along the intestine. After 7 days there was a gradual posteriad spreading of the scolex attachment sites and of the parasite biomass. Hymenolepis diminuta can attach itself anywhere in the anterior 75% of the intestine, including in front of the opening of the bile duct: no worms were found in the small intestine extending back into the caecum.The pattern of migration and the changes in worm distribution in the intestine suggest that H. diminuta selects an appropriate, but changing position, on one or more of the gradients that have been demonstrated or postulated along the length of the small intestine.It is also suggested that the long-term migration during prepatent development is interrelated, but distinct from the daily migrational movements that H. diminuta undergoes within the small intestine.