Effects of source of metacercariae on experimental infection of Zygocotyle lunata (Digenea: Paramphistomidae) in CD-1 mice.

Outbred (CD-1 strain) mice were infected experimentally with metacercariae of Zygocotyle lunata obtained from naturally infected Helisoma trivolvis. Growth, survival, and fecundity of the parasite and gross pathology in the host were evaluated. Metacercariae from 5 snail sources produced 3 patterns of growth and survival: significantly smaller worms that survived less than 4 wk and did not mature, significantly larger worms that matured but survived less than 6 wk, and worms of intermediate size that matured and lived at least 19 wk. Parasite maturation (at 3-4 wk) and egg production (14 eggs.worm-1.hr-1) were similar among infections from different sources. Ceca of mice with infections at least 4 wk old were enlarged with localized mucosal alteration at the site of parasite attachment, but there was no evidence of splenomegaly. The differences in infection due to the source of metacercariae within 1 strain of final host were similar to differences reported among other species of final host. These results suggest that variation associated with the intermediate host may confound studies of specificity to the definitive host.