Studies on the reproductive capacity of Echinostoma caproni (Trematoda) in hamsters and jirds.

Total egg output per infective stage inoculated was used as a measurement of the reproductive capacity in Echinostoma caproni infections in hamsters and jirds. Egg production per adult E. caproni recovered was comparable in the hamster and in the jird, but the reproductive capacity of E. caproni in infections with 6 metacercariae in the hamster markedly exceeded that in the jird. This was due mainly to the expulsion of worms from the jird. Eggs per gram faeces produced was shown to be an invalid parameter in comparing the reproductive capacity in E. caproni infections in jirds and hamsters due to differences in amounts of faeces produced, and evidence was obtained that uterine egg counts may not be a useful parameter in assessment of overall reproductive potentials. In the hamster, the reproductive capacity of infections with 25 or 6 metacercariae of E. caproni was comparable. This reflected a density independent recovery and egg production of the adult worms. The reproductive capacity, being an expression of the importance of a particular host species for the reproduction of a parasite population, is suggested as a convenient and useful quantitative parameter in the establishment of standardized criteria for evaluating host-parasite relationships in definitive host models.