Are snakes in Honshu facing tough times?

A research group, including Harushige Seo (an undergraduate student), Eriko Ansai (a graduate student), Tetsuya Sase (an undergraduate student), Associate Professor Tsukasa Waki, and Lecturer Yosuke Kojima from the Faculty of Science, Toho University, discovered a new North American trematode, Ochetosoma elongatum, for the first time in Japan in the oral cavities of three native snake species in the Kanto region. In addition to investigating its life cycle in the wild, the authors conducted a comprehensive literature review to explore the route of invasion of this parasite. The findings of this study were published in Parasitology International on August 24, 2024.

Key Points

• Ochetosoma elongatum is a snake trematode which distribute in North America. However, the adult was discovered for the first time in Japan in the mouths of three native snake species in the Kanto region. A previous study reported the presence of a related North American trematode (Ochetosoma kansense) in western Japan, indicating that the two North American trematodes are now infecting native snakes in Japan.
• The sporocysts and cercariae were detected in the North American freshwater snail Physella acuta, which has introduced and established its population in Japan. The cercarae is thought to infect frogs and develop into metacercariae. The metacercariae develop into adults after the host frog was fed by the Japanese snakes, the definitive host.
• The snail Physella acuta are thought to be introduced to Japan with imported freshwater plants for aquarium. The increased demand for ornamental fish and exotic pets likely led to the introduction of infected Physella acuta snails and/or North American snakes, resulting in the introduction of this parasite to Japan.