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Paragonimus westermani infection of freshwater crab Sundathelphusa philippina and melaniid snails in Cadacan River in Irosin, Sorsogon, Philippines

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Paragonimiasis, the disease caused by Paragonimus westermani, is transmitted primarily by freshwater crabs Sundathelphusa philippina in the Philippines. Human infection has been recorded, but there is a dearth of published information on the extent of infection in animal reservoirs, particularly in crabs and snails. This study aimed to investigate the infection status and risk factors of P. westermani in freshwater crabs and melaniid snails collected in an endemic village along Cadacan River in Irosin, Sorsogon, where human cases of paragonimiasis were previously reported. A total of 246 freshwater crabs (118 females, 128 males) were dissected, and the gills, muscles, gonads, and viscera were examined for the presence of metacercariae; of which, 41.87% were found infected. The metacercariae were recovered from the gills (100%) and muscle tissues (7.3%) of infected crabs. Male crabs were more likely to be infected (49.22%) than female crabs (33.90%) (p < 0.05). Moreover, 70.87% of crabs showed low parasite intensity levels at ≤ 30 metacercariae/g tissue. A negative weak correlation was observed between parasite intensity and crab weight and carapace length, i.e., highly infected crabs were found to be smaller in size. Meanwhile, only 12% of the 150 melaniid snails collected were positive with cercariae with Tarebia granifera and Jagora asperata as the most infected species. Household survey conducted revealed that some knowledge, attitudes, and practices of the locals contribute to the sustained transmission of the parasite in this endemic area. These findings revealed that P. westermani is still prevalent among intermediate hosts and that some social and environmental factors contributed to the sustained parasite transmission in this endemic community.

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All data generated or analyzed during this study are included in this published article [and its supplementary information files].


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The authors would like to thank Carriedo local government unit in Sorsogon, Philippines for their assistance during the data collection and the Parasitology Research Laboratory of the Animal Biology Division of the Institute of Biological Sciences, University of the Philippines Los Baños for the use of facilities and laboratory assistance.


There was no financial support for this study.

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All authors contributed to the study conception and design, material preparation, data collection, and analysis. The first draft of the manuscript was written by VGP, JAS, and KLP and the rest made comments and revisions to the final manuscript.

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Correspondence to Vachel Gay Paller.

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The authors have no conflict of interest.

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The authors declare compliance with all relevant ethical standards. Gratuitous permit was secured from the Department of Environment and Natural Resources (DENR)—Region V and clearance from the local government unit (LGU) of Irosin, Sorsogon.

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Informed consent was obtained from all individual participants included in the study.

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Paller, V.G., Samudio, J.A., Patagnan, K.L. et al. Paragonimus westermani infection of freshwater crab Sundathelphusa philippina and melaniid snails in Cadacan River in Irosin, Sorsogon, Philippines. J Parasit Dis 45, 634–642 (2021).

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