HOST SPECIES, HOST SIZE, AND MIRACIDIAL DOSE INFLUENCE THE INFECTION SUCCESS OF ECHINOSTOMA TRIVOLVIS LINEAGE C LARVAE.

Completing parts of trematode life cycles in the laboratory is a useful way to obtain experimentally infected hosts and identify how specific aspects of parasitism influence host ecology and behavior. However, a lack of knowledge about host specificity and other factors that influence prevalence can hamper those efforts. Echinostoma trivolvis lineage c is a genetically distinct member of the E. trivolvis species complex that is known only from DNA sequences from adult and larval stages recovered from naturally infected muskrats (Ondatra zibethicus) and the marsh pondsnail (Ladislavella elodes), respectively. We determined the effect of host species/morphotype, host size, and miracidial dose on the infection success in potential first intermediate hosts. In the laboratory, we exposed 2 freshwater snail species (L. elodes and Planorbella duryi) and a morphological variant of L. elodes (formerly known as Stagnicola reflexa) to 2 miracidia to determine first intermediate host use. Among these 3 snail groups, we also tested the effect of host size on infection success with 3 size classes (1-5 mm, 5-10 mm, and 10-15 mm). Within 1 host species, L. elodes, we compared the effect of 2 doses (2 and 5 miracidia) and 3 size classes on infection success. At a dose of 2 miracidia, rediae and cercariae developed within 1 host species, L. elodes, as well as the S. reflexa morphotype, although infection success varied according to host size. At a dose of 5 miracidia, infection success increased in small and medium-size L. elodes relative to the low dose group. Our results confirm the first intermediate host species observed in nature but indicate that prevalence is influenced by host species morphotype, host size, and parasite dose. To obtain more infected snails, our experiments suggest exposing small and medium-size L. elodes snails to 5 miracidia. This research encourages further use of E. trivolvis lineage c in the laboratory to explore aspects of host-parasite interactions such as parasite-modified behavior.