Lung fluke (Paragonimus skrjabini miyazakii) infection of a freshwater crab (Geothephusa dehaani) in the Kamiyakawa and Yoshihara Streams

Abstract

The lung fluke, Paragonimus skrjabini miyazakii, is a parasitic flatworm of the class Trematoda. This parasite is transmitted via snails (the first intermediate hosts) to the Japanese freshwater crab Geothephusa dehaani (the second intermediate host), and finally to mammals including humans. The zoonosis that develops when mammals ingest the freshwater crab is termed paragonimiasis. To investigate the prevalence of the lung fluke in the second intermediate host, freshwater crabs were collected from the Kamiyakawa and Yoshihara Streams of Kochi Prefecture. The lung fluke infection rates were analyzed in terms of crab body size, color, and within-stream density. The infection rates were considerably elevated (49.2–60%) in certain Yoshiwara upstream regions that were both small and exhibited high crab densities. The infection rate differed by crab body size and color. The crab may be blue, red, or brown; it remains unknown how the color variations are controlled. The infection rate of red crabs (with the pigment astaxanthin) was lower than that of blue crabs (without the pigment), suggesting that astaxanthin could reduce parasitic infection.