The expulsion of Echinostoma trivolvis (Trematoda) from ICR mice: scanning electron microscopy of the worms.

Echinostoma trivolvis adults are rejected from ICR mice within 3 weeks postinfection (p.i.) but are retained in golden hamsters for greater than 15 weeks. The present study used scanning electron microscopy (SEM) to examine worm topography in ICR mice, particularly that of the collar spines, and to correlate worm loss with tegumentary changes. The topography of the worm in ICR mice was similar to that observed in previous studies on this echinostome in domestic chick embryos, chickens, and golden hamsters. Observations were made on the pattern of collar spines in 115 worms from ICR mice at 3-14 days p.i. All worms examined at 3 days exhibited extended spines, whereas about 70% of the worms examined at 14 days displayed retracted or missing spines. Eight worms from golden hamsters examined at 14 days p.i. showed extended collar spines. The retraction or loss of collar spines may play a role in the expulsion of E. trivolvis from ICR mice.