Molecular detection of Paragonimus mexicanus in freshwater crabs: new records in Oaxaca, Mexico.

Paragonimiasis is a zoonotic disease caused by lung flukes of the genus Paragonimus, which use freshwater snails and crustaceans as intermediate hosts and mammals as definitive hosts. Despite its public health importance, few studies have documented the distribution of this parasite in tropical regions of Mexico. In April 2024, a total of 180 freshwater crabs of the genus Pseudothelphusa were collected from five localities in Oaxaca State, Mexico. Metacercariae were observed in 47.2% of the crabs examined, with the highest mean intensity (18.46 cysts per crab) recorded in San Pedro Molinos locality. Morphologically, the metacercariae corresponded to Paragonimus mexicanus, although a distinct pink morphotype resembling P. caliensis was detected in San Juan Cacahuatepec locality. Molecular identification based on the 28S rRNA gene confirmed a 98.51% to 98.72% similarity with P. mexicanus (GenBank accession no. HM172619.1). This study provides new molecular records of P. mexicanus in freshwater crabs from previously unsampled localities in Oaxaca, expanding the known geographic distribution of the parasite in southern Mexico. Continuous surveillance and molecular characterization of Paragonimus species are essential to clarify their diversity and assess zoonotic risk in Neotropical freshwater systems.