Avian schistosomes, mainly belonging to the genus Trichobilharzia, are the etiological agents of cercarial dermatitis in humans. The aims of this study were to report a human case of cercarial dermatitis contracted in a paddy field in a natural regeneration area in Tokyo, Japan, and identify the etiological agents of this case using molecular phylogenetic analyses. A snail survey was conducted between 2021 and 2023 in a rice paddy field where a case of cercarial dermatitis occurred, and molecular phylogenetic analyses of the furcocercariae and parasitized lymnaeid snails were performed based on the partial sequence of the mtDNA cox1 gene. Furcocercariae were detected in 11 (2.7%) of the 413 lymnaeid snails examined, and all 120 pleurocerid snails tested negative for cercariae. The cercarial larvae possessed a pair of eye spots and a characteristic bifurcated tail. Phylogenetic analyses of the cox1 genes identified the furcocercariae as Trichobilharzia sp., and the lymnaeid snails were Radix plicatula. This study demonstrated that the life cycle of a Trichobilharzia sp., using R. plicatula as an intermediate host, is established in an urban natural restoration area in Tokyo, serving as a source of human cercarial dermatitis. This study emphasizes the need for an increased awareness of cercarial dermatitis as a potential public health concern.
To determine that Paragonimus sp. is actively transmitted in a tropical area of the Pacific region of Ecuador where human cases of pulmonary paragonimiasis have recently been documented, a total of 75 freshwater crabs were collected from 2 different streams in the Pedernales area of Manab? Province, Ecuador. All collected crabs were identified as Hypolobocera guayaquilensis based on morphological characteristics of the male gonopods. The hepatopancreas of each crab was examined by compressing it between 2 glass plates followed by observation under a stereomicroscope. Excysted Paragonimus metacercariae were detected in 39 (52.0%) crabs and their densities varied from 1 to 32 per infected crab. There was a positive relationship between crab size and metacercarial density. Sequences of the second internal transcribed spacer region of the ribosomal RNA gene of the Paragonimus metacercariae obtained in this study were identical to those of Paragonimus mexicanus deposited in the DDBJ/EMBL/GenBank database. Thus, the present study is the first to confirm that the crab species H. guayaquilensis is the second intermediate host of P. mexicanus in Manab? Province, Ecuador. Because this crab might be the possible source of human infections in this area, residents should pay attention to improper crab-eating habits related with a neglected parasitic disease, i.e., paragonimiasis.
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