Current Status of Lung Fluke Metacercarial Infection in Freshwater Crabs in the Kawane Area of Shizuoka Prefecture, Japan

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Feline cases of lung fluke infection were recently reported in the upper basin of the Oi River in Shizuoka Prefecture. The causative species of these cases were not identified, although a field survey conducted about 40 years ago in this area demonstrated the prevalence of Paragonimus miyazakii metacercariae in intermediate host crabs. To clarify the current status of lung fluke metacercarial infection in host crabs, we collected the Japanese freshwater crab or Sawagani, Geothelphusa dehaani, at 14 sampling sites in the Kawane area, which is located in the upper basin of the Oi River. Sawagani harboring Paragonimus metacercariae were collected at all sampling sites in this study with a total prevalence of 42% (281 of 677 crabs examined) and a range of 16 to 92%. The number of metacercariae per infected crab ranged from 1 to 19 with a mean of 2.2. Based on the morphological features of the metacercariae and adult worms recovered from rats that were experimentally infected with the metacercariae, the lung flukes examined were identified as P. miyazakii Kamo, Nishida, Hatsushika and Tomimura, 1961; ITS2 sequence data corroborate this conclusion. P. miyazakii is still widely prevalent in this area, implying that the recently reported feline paragonimiasis cases were likely caused by P. miyazakii infection.