Immunological status of some edible fishes exposed to parasitic infections in relation to heavy metals pollution

Prevalence and identification of cyathocotylid trematodes infecting African catfish in Egypt

The trematode family Cyathocotylidae infects various hosts worldwide, including birds, mammals, reptiles, and fish. However, the lack of molecular data from adult worms hinders phylogenetic, epidemiological, and host association studies. This study aims to identify the common cyathocotylid trematodes infecting African catfish in Egypt using morphological and molecular evidence. Out of 142 Clarias gariepinus, 123 fish (86.6%) harbored cyathocotylid metacercariae, with a mean metacercarial intensity of 201 ± 38.5/g. Cyathocotylid metacercariae prevalence gradually rose as host size increased. Although there was no significant difference between groups, larger fish had a higher mean metacercarial intensity. The prevalence and intensity were unrelated to the fish gender. Histopathological examination of metacercariae-infected catfish revealed varying degrees of degenerative changes, including intermuscular edema leading to muscle fiber dispersion and atrophy, involving 11% to over 81% of muscle sections. We identified three cyathocotylid metacercariae and eight cyathocotylid adult species from experimental infection using morphometric and molecular data, including internal transcribed spacer (ITS) and/or mitochondrial cytochrome c oxidase subunit 1 (cox1) sequences. We determined the phylogenetic position of these cyathocotylid samples. The ITS sequence analysis linked the isolated Cyathocotylidae sp. 1 and 2 metacercariae to Prohemistomum vivax adults. Mesostephanus appendiculatoides and Paracoenogonimus ovatus were reported for the first time in Egypt. These findings may provide valuable genetic data for future molecular epidemiological and phylogenetic studies of cyathocotylid trematodes.

Tissue Accumulation, Cytotoxicity, Oxidative Stress, and Immunotoxicity in African Catfish, Clarias gariepinus Exposed to Sublethal Concentrations of Hexavalent Chromium

Hexavalent chromium (Cr6+) is one of the stable oxidation states of chromium that has been reported to elicit various toxic effects in aquatic organisms. However, the mechanisms of Cr6+ toxicity are still poorly understood. Thus, the present study investigated the tissue accumulation, cytotoxic, oxidative stress, and immunotoxic effects of Cr6+ in juvenile Clarias gariepinus. The fish were exposed to waterborne Cr6+ concentrations (0, 0.42, 0.84, and 1.68 mg/L) for 28 days, after which they were sacrificed and various organs were harvested for the determination of Cr6+ levels. Other parameters that were indicators of oxidative stress, cytotoxicity, and immunotoxicity were measured. Cr6+ accumulated more in the kidney and liver of the exposed fish, especially at the highest concentration. The levels of lipid peroxidation and DNA fragmentation increased significantly in the exposed fish. The activities of superoxide dismutase and lactate dehydrogenase increased significantly in exposed fish compared to the control. The total white blood cells, lymphocytes, and neutrophils counts were significantly higher in the exposed fish compared to the control fish. The respiratory burst activity decreased significantly in the exposed fish while the myeloperoxidase content did not differ significantly. There were upregulations of TNF-α and HSP 70 while CYP II and MHC 2 were downregulated in the exposed fish. Also, exposure to Cr6+ resulted in various histopathological alterations in the architecture of the head kidney. The results indicate concentration-dependent toxic effects of Cr6+ in C. gariepinus. The study reveals the potentials of Cr6+ to accumulate in the different tissues of fish and caused cytotoxic, oxidative stress, and immunotoxic effects in the exposed fish.

Immune pathogenesis in pigeons during experimental Prohemistomum vivax infection

Prohemistomum vivax is a small trematode belonging to the family Cyathocotylidae, infecting fish-eating birds and mammals, including humans. However, no data on molecular identification and immune pathogenesis are available, challenging effective diagnostic and therapeutic interventions. Here, we identified P. vivax based on combined morphological and molecular data and examined histopathological lesions and the differential cytokines expression in experimentally infected pigeons. Pigeons were orally infected with 500 prohemistomid metacercariae. Intestinal and spleen tissues were harvested 2, 4, 7, 14, 21, and 28 days post-infection (dpi). Gene expression levels of eleven cytokines (IL-1, IL-2, IL-4, IL-5, IL-6, IL-10, IL-12, IL-15, IL-18, IFN-γ, and TGF-β3) were assessed using quantitative reverse-transcription PCR (RT-qPCR). We identified the recovered flukes as Prohemistomum vivax based on morphological features and the sequence and phylogenetic analysis of the internal transcribed spacer 1 (ITS1), 5.8 ribosomal RNA, and ITS2 region. Histopathological lesions were induced as early as 2 dpi, with the intensity of villi atrophy and inflammatory cell infiltration increasing as the infection progressed. An early immunosuppressive state (2 and 4 dpi), with TGF-β3 overexpression, developed to allow parasite colonization. A mixed Th1/Th2 immune response (overexpressed IFN-γ, IL-12, IL-2, IL-4, and IL-5) was activated as the infection progressed from 7 to 28 dpi. Inflammatory cytokines (IL-1, IL-6, IL-18, and IL-15) were generally overexpressed at 7–28 dpi, peaking at 7 or 14 dpi. The upregulated Treg IL-10 expression peaking between 21 and 28 dpi might promote the Th1/Th2 balance and immune homeostasis to protect the host from excessive tissue pathology and inflammation. The intestine and spleen expressed a significantly different relative quantity of cytokines throughout the infection. To conclude, our results presented distinct cytokine alteration throughout P. vivax infection in pigeons, which may aid in understanding the immune pathogenesis and host defense mechanism against this infection.