Effects of a 300-metacercarial cyst inoculum on worm recovery and crowding of Echinostoma caproni in Balb/C mice.

To test the effects of a large metacercarial cyst inoculum on the recovery of Echinostoma caproni adult worms in Balb/C mice, 4 mice were each exposed to 300 cysts and necropsied 21 days PI. The number and percent recovery of worms in the four hosts were 43 (14.3%), 54 (18.0%), 86 (28.7%), and 102 (34.0%). These recoveries were all higher than those in a previous report of 22 (7.3%) worms recovered from a single Institute of Cancer Research (ICR) mouse exposed to 300 cysts 22 days prior to necropsy. Our study showed that a large cyst inoculum (e.g. 300) can be used to obtain approximately 100 patent worms per host within 3 wk PI. We also showed that there was a significant decrease in body area and uterine egg counts in worms from the host that had the greatest number of worms compared to those that were obtained from hosts with lower worm burdens.