Euclinostomum heterostomum and E. ardeolae in tilapia species of Aswan Governorate, Egypt: morphological, molecular, and histopathological characterization

Euclinostomum heterostomum and Euclinostomum ardeolae , both encysted metacercariae (EMC), were found to infect farmed Oreochromis niloticus in the Sahary fish hatchery and wild O. niloticus , Sarotherodon galilaeus , and Tilapia zillii in Lake Nasser, Aswan Governorate, Egypt, at a prevalence of 25.25% and an infection intensity of 1–14 EMC/fish. Macroscopic and microscopic examinations were used to identify them morphologically. PCR amplification, sequencing of the 28S large ribosomal RNA region, and phylogenetic analysis were used for molecular characterization. E. heterostomum and E. ardeolae were isolated from farmed O. niloticus kidneys, peritoneum, abdominal cavity, and under the gills attached to the head bone at prevalence of 13.5% and 6%, respectively, and from wild O. niloticus , S. galilaeus , and T. zillii at a prevalence of 15% and 4.5%, 18% and 10%, and 22.5% and 11.5% respectively. The molecular analyses of rRNA-28S marker revealed that the two Euclinostomum species examined are related yet distinct. This is the first molecular and phylogenetic evidence linking E. ardeolae to Euclinostomum . The present study added two new sequences to the GenBank databases for the genus Eulinostomum from Egypt, with accession numbers MW604803 and MW604806. Euclinostomum spp. have been shown to have detrimental and destructive effects on the kidneys of infected fish; these effects may eventually result in the parasites’ cysts replacing the kidney’s tissues. The kidneys of tilapia spp. infected with Euclinostomum spp. displayed degenerative alterations, with dilated renal tubules associated with migratory tunnels composed primarily of leucocytic infiltrations. Euclinostomum spp. exhibited clear hemophagic characteristics.