4. Echinostoma revolutum. a. Adult worm. Echinostomes are intestinal parasites with a worldwide distribution. Infection results from ingesting metacercariae, usually in uncooked molluscs. Mammals and birds serve as reservoir hosts. Heavy infections may cause diarrhea. Structures visible are two tandem testes (T), faintly-stained ootype (O), ovary (OV), uterus (U) filled with eggs, acetabulum (A), and seminal vesicle (S). Extensive vitelline glands (V) occupy lateral margins. b. Newly formed eggs in the uterus, which are passed out unembryonated in the feces of the definitive host. c. Collar of spines surrounding mouth, the feature that gives echinostomes their name. Life cycle: adult in small intestine of definitive host -- egg in feces -- 2 wk -- miracidium -- penetrates snail (1st intermediate host) -- sporocyst -- produces many -- mother rediae -- each produces many -- daughter rediae -- each produces many -- cercariae -- penetrate 2nd intermediate host (mollusc) -- metacercaria -- ingested by definitive host -- adult
6. Eggs of Echinostoma paraensei. Unembryonated when first deposited in the feces, a miracidium develops within two weeks and hatches through a small operculum (bottom right two photos). Compare with eggs of Fasciola hepatica .
