Evaluation of the antiparasitic efficacy of praziquantel against Prohemistomum vivax (Cyathocotylidae) metacercariae in naturally infected African catfish (Clarias gariepinus)

Abstract

Prohemistomum vivax (Cyathocotylidae) is a significant parasitic threat in Egyptian African catfish (Clarias gariepinus) aquaculture, causing tissue damage, high prevalence, and economic losses. This study evaluated the dose-dependent efficacy of praziquantel against naturally occurring P. vivax encysted metacercariae (EMC) under controlled laboratory conditions and explored its potential mode of action via molecular docking. A total of 105 naturally infected catfish (150-250 g) were randomly assigned to seven groups. Each treatment consisted of three independent replicate tanks (experimental units), with five fish per tank (n = 15 fish per treatment). Treatments included a control group (0 mg/L) and six praziquantel groups administered as single doses (0.5, 2, or 3 mg/L for 24 h) or double doses repeated after 7 days. Parasitological, histopathological, and pro-inflammatory gene expression analyses (TNF-α, IL-1β) were performed. The highest efficacy was achieved with double-dose 3 mg/L, resulting in 94.2 ± 2.1% parasite reduction (p < 0.001), with clear dose-dependent trends (single-dose: 28.8-67.9%; double-dose: 43.7-94.2%). Histopathological analysis showed reduced cyst burden and tissue lesions, while inflammatory markers were significantly downregulated in treated groups. To investigate praziquantel's mechanism of action, in silico docking targeted P. vivax cytochrome c oxidase subunit I (COI), a key mitochondrial enzyme. Praziquantel exhibited strong binding affinity (-6.1 kcal/mol; RMSD = 0.0 Å), forming stable hydrophobic interactions with conserved residues (Val55A, Ala58A, Leu88A, Phe91A, Trp142A). The localization of Trp142A within the active site suggests potential enzyme inhibition, supporting a mitochondrial mechanism of action. These findings confirm praziquantel's effectiveness against P. vivax EMC and identify COI as a potential molecular target. Given its critical role in human medicine, further research into resistance risks, environmental safety, and regulatory frameworks in aquaculture is recommended.