Light and scanning electron microscopy of Echinostoma caproni (Trematoda) during maturation in ICR mice

Light (LM) and scanning electron microscopy (SEM) were used to study the maturation of Echinostoma caproni in 13 ICR mice, each of which was exposed to 50 encysted metacercariae and necropsied at 1-20 weeks postinfection (p.i.). All 13 mice were infected with 20-30 worms/host and half the worms were used for LM and the remainder, for SEM. Body area measurements showed that the worms grew rapidly from day zero (excysted metacercariae) to 4 weeks p.i. and less rapidly thereafter. Area measurements of organs showed that the growth of the acetabular area paralleled that of the body. Gonadal area growth was less rapid than acetabular growth, and the area of the posterior testis was always greater than that of the anterior testis. The most remarkable change in topography occurred by 5 weeks p.i. when some of the ventral tegumentary spines became multipointed with 2-5 points/spine. Spine division was associated with a decline in worm growth, but the significance of this finding is unclear. Spine division probably facilitates the feeding, abrasion, and migration of this echinostome in the mouse small intestine.