Infectivity, growth, distribution and fecundity of a six versus twenty-five metacercarial cyst inoculum of Echinostoma caproni in ICR mice

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Abstract
Female ICR mice, 6–8 weeks old, were exposed to 6 (group A) or 25 (group B) metacercarial cysts/host of Echinostoma caproni to determine the effects of these cyst dosages on infectivity, growth, distribution and fecundity of worms in the small intestines. All 30 mice exposed (15 in group A and 15 in group B) were infected and there was no significant difference in the percentage of worm recovery between group A and B at 2, 4 and 8 weeks postinfection (PI). Growth was rapid in both groups with worm body areas increasing from about 3mm2 at 2 weeks PI to about 7 mm2 at 8 weeks PI. More worms from group B were in the anterior sections of the small intestines at 2 and 4 weeks PI than those from group A. However, at 8 weeks PI more worms from Group A were in the anterior sections of the small intestines than those from group B. There were marked differences in our findings on infectivity, growth and distribution of E. caproni in ICR mice using 6 and 25 cyst inocula compared to a previous study using the same echinostome and cyst inocula in NMRI mice, presumably related to the mouse strain. Fecundity studies were somewhat comparable in both studies showing an approximate three to four times increase in the average number of eggs/gram of faeces in mice receiving 25 versus 6 cyst inocula.