Infectivity, growth and distribution of preovigerous adults of Echinostoma caproni in ICR mice.

All 23 6-8-week old outbred female ICR mice, each fed 100 metacercarial cysts of Echinostoma caproni, were infected on days 2, 4, 6, and 8 postinfection (PI) with a mean of 45 worms/host. To examine worm distribution in the mouse, the small intestine was divided into five equal sections (segments 1-5 beginning with the pylorus). Worms were found mainly in segments 3 and 4 and were never found in segment 1. Mean body area of worms fixed in 10% neutral buffered formalin (NBF), hot alcohol-formalin-acetic acid (AFA) and aceto-carmine increased slowly until day 4 and then rapidly until day 8 PI. There was a significant difference in the mean body area of worms fixed in hot AFA, NBF, and aceto-carmine on all days except 4 and 6. Distinction of the ovary and ootype was apparent by day 6 and uterine cooling was observed by day 8 PI. Only 2 of 50 worms showed eggs in the uterus on day 8 PI.