The Life Cycle of Metagonimoides oregonensis Price (Trematoda: Heterophyidae)

Metagonimoides oregonensis (Heterophyidae: Digenea) Infection In Pleurocerid Snails and Desmognathus quadramaculatus Salamander Larvae In Southern Appalachian Streams

“…Metagonimoides using Juga (5Oxytrema) silicula either form metacercariae within the snails or produce free-swimming cercariae that then form metacercariae in Rana spp. frogs (Burns and Pratt, 1953). The latter authors experimentally confirmed that cercariae could penetrate red-legged frogs, Rana aurora, which was suggested to be a common natural host for the parasite, as well as leopard frogs, Rana pipiens, and bullfrogs, Lithobates catesbeianus (5Rana catesbeiana).…”

“…Previous descriptions of the cercariae (Ingles, 1935;Burns and Pratt, 1953) refer to a tail emerging from a deep socket, with a dorso-ventral finfold starting half-way down the tail and continuing down to the tip (pleurolophocercous type). Our SEM images show the deep socket and dorso-ventral finfold, but also a lateral finfold starting at the tail's base that diminishes around the tail's midpoint ( Fig.…”

“…Emerging cercariae were removed from the cups with a pipette, placed on slides, and viewed and photographed using both brightfield viewing, following staining with neutral red, and darkfield viewing with no staining. Initial identifications were done using Schell (1985) and, for the most abundant cercariae that were being shed, which were tentatively identified as M. oregonensis, they were also compared with the description of Burns and Pratt (1953). Several cercariae samples from individual snails were preserved in 95% ethanol and stored at 220 C for subsequent molecular sequencing.…”

“…Soon after, definitive host surveys established the presence of this trematode across much of the United States, from North Carolina to Oregon, and subsequently the life cycle was experimentally determined in the laboratory (Burns and Pratt, 1953). Raccoons, and possibly mink, appear to be the primary definitive hosts, with adult parasites found in the small intestine.…”

“…Eggs are passed in the feces, and miracidia infect stream-dwelling prosobranch snails, which serve as the first intermediate host. It remains unknown whether the miracidia are free-swimming or must be consumed by the first intermediate host snails (Burns and Pratt, 1953 (5Goniobasis, Dillon, 2011). Cercariae develop within rediae in the snails; there is no sporocyst stage.…”