Characterization of Clinostomum cutaneum and Clinostomum phalacrocoracis in tilapia species of Aswan Governorate, Egypt: A morphological, molecular and histopathological study

Abstract

Clinostomum species are digeneans, and their metacercariae infect both cultured and wild fish worldwide, causing significant economic losses and possibly possessing zoonotic potential; identification of these parasites has proven challenging due to the high degree of similarity and minor differences between different species. To identify them, we used a combination of morphological and molecular methods. Only tilapia species were positive for clinostomatids among 1200 examined fish samples from Aswan Governorate, Egypt (Oreochromis niloticus, Sarotherodon galilaeus, Tilapia zillii, Lates niloticus, Synodontis schall, Synodontis serratus and Hydrocynus forskalii). Clinostomum cutaneum and Clinostomum phalacrocoracis were isolated from cultured O. niloticus with a prevalence of 25% and 11.5%, respectively, and from wild O. niloticus, S. galilaeus and T. zillii with a prevalence of 12.5% and 27.5%, 23% and 33%, and 7.5% and 16.5% respectively. The nuclear ribosomal gene marker (28S rRNA) was amplified using PCR and sequenced, followed by phylogenetic analysis, which revealed that the two species under investigation were very closely related to C. cutaneum and C. phalacrocoracis. The histopathological changes associated with clinostomatid infections are necrosis, tissue damage and immune cell infiltration at the site of infection. C. cutaneum metacercaria was characterized for the first time in Egyptian fish. It was pathogenic to tilapia and caused significant mortality in cultured conditions.