Characteristics of pathology and transcriptome profiling reveal features of immune response of acutely infected and asymptomatic infected of carp edema virus in Koi

Transcriptome analysis of head kidney and liver in grass carp (Ctenopharyngodon idella) symptomatically or asymptomatically infected with Flavobacterium columnare

Flavobacterium columnare is an important pathogen causing columnaris disease, which can result in high mortality in freshwater fish worldwide. Understanding the immune response in infection status of fish may be essential for developing effective prevention and treatment strategies. In this study, transcriptomes of liver and head kidney tissues in grass carp (Ctenopharyngodon idella) were compared under symptomatic and asymptomatic statuses following the immersion infection of F. columnare. Significant differences in expression of genes were observed between fish showing disease symptoms and those without symptoms. The number of differentially expressed genes (DEGs) between infected and control groups ranged from 4752 to 8,277, while the DEGs between exposed and control groups ranged from 272 to 1,751, suggesting a strong acute inflammatory response in infected groups. KEGG pathway enrichment analysis of infected groups revealed that among the top 30 enriched pathways, liver and head kidney shared 22 and 16 common pathways, respectively. These common enriched pathways are involved in various functions such as metabolism, diseases, cellular processes, biological systems, and information processing, indicating their roles in the immune response to F. columnare. Notably, we investigated in detail the gene expression profiles associated with complement molecules and three classes of cytokines (interleukin, tumor necrosis factor, and interferon) in different organs/tissues and disease states during the pathogenesis of columnaris disease. The findings highlight the importance of inflammatory responses and complement pathways in the pathogenesis of columnaris disease and suggest potential targets for future research and disease management strategies. The present study thus provides valuable insights into the transcriptomic changes and immune responses in grass carp infected with F. columnare, and sheds light on how highly virulent strains of F. columnare cause morbidity and mortality in the host.

Potential to grow carp oedema virus (genogroup I) in monolayers of carp-derived primary cells with further implication in cell analysis

Carp oedema virus (CEV) has distinct molecularly identified genogroups of viral mutations, denoted as I, IIa, and IIb. Failure to propagate CEV in vitro limits studies towards understanding its interactions with host cells. Here, virus isolates belonging to genogroup I collected during natural outbreaks in the Czech Republic were employed for routine CEV cultivation in monolayers of carp-derived primary cells, common carp brain (CCB) cells, and epithelioma papulosum cyprinid (EPC) cells. Induction of cytopathic effects (CPEs) was observed and recorded in affected cells. Cell survival rate was evaluated under serial dilutions of the CEV inoculum. Virus cell entry was quantified and visualized by qPCR and transmission electron microscopy, respectively. Study findings indicate primary gills epithelia likely present the most suitable matrix for CEV growth in vitro. Cells of the head kidney and spleen facilitate virus entry with microscopically confirmed CPEs and the presence of cytoplasmic pleomorphic virus particles. Cells of the trunk kidney and gonads are unlikely to permit virus cell entry and CPEs development. Although CEV cultivation in cell lines was inconclusive, EPC cells were CEV permissible. Monolayers of carp-derived primary cells show promise for CEV cultivation that could enable elaborate study of mechanisms underlying cellular binding and responses.

Distribution of carp edema virus in organs of infected juvenile common carp

Introduction

The disease caused by carp edema virus (CEV) manifests with lethargy as a primary sign; this observation in koi in Japan gained the disease the name koi sleepy disease (KSD). In the years following the discovery of the virus in Japan, KSD cases have been noted in the UK in koi and common carp. Conducting research in order to expand knowledge of the processes of distribution of CEV in infected fish organs will be helpful for eradication and diagnostic purposes.

Material and Methods

Carp edema virus-affected fish with clinical signs of KSD were experimentally cohabited with common carp fry (30 fish). Three fish were euthanised by bath in a 0.5 g L-1 tricaine solution at one week intervals (7, 14, 21 and 28 days post cohabitation). Tissue samples from the brain, gills, spleen, kidney, intestines and skin were collected, and the total DNA was extracted and tested by real-time PCR.

Results

By the seventh day post infection, CEV DNA was most often found in the skin, gills and brain and less frequently in the kidney and intestines. In many of the common carp fry, CEV DNA could typically be found in several organs of each individual fish, although it was only found in one sample of spleen tissue.

Conclusion

In this experimental study the pathogenesis of the CEV infection process was shown, the high infectivity of CEV was confirmed and the best organs were determined for sampling in CEV-infection experimentation. The real-time PCR method used in our cohabitation experiments was shown to be useful at the clinical and asymptomatic stage of virus infection.