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Impact of virus-induced gill disease caused by carp edema virus (CEV) on the immunological status of fish

Applicant Dr. Mikolaj Adamek
Subject Area Veterinary Medical Science
Term from 2019 to 2023
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 426513195
 
Final Report Year 2025

Final Report Abstract

Viral gill diseases seriously affect fish health and have a high negative impact on aquaculture, mainly because of the multifunctional involvement of gills in fish physiology. In the project entitled “Impact of virus-induced gill disease caused by carp edema virus (CEV) on the immunological status of fish (CARPCEV)” funded by DFG and NCN in the frame of the BEETHOVEN LIFE 1 program, we studied the carp edema virus (CEV), a fish-infecting poxvirus which affects predominantly the gills of common carp (Cyprinus carpio) and induces a severe gill disease known as koi sleepy disease (KSD) causing severe mortality. Our goal was to determine whether differential stress responses, stress sensitivities, and immune responses might affect the outcome of KSD in carp strains (koi and Amur Sazan - AS). Second, we tested whether severe immunosuppression induced during KSD could impact susceptibility to secondary infections and the general immunological status of survivors during and after CEV infection. Additional research was conducted using cyprinid herpesvirus 3 (CyHV-3), spring viremia of carp virus (SVCV), and tilapia lake virus (TiLV) models to compare effects, better understand viral gill diseases, and search for solutions to the threat posed by CEV. We demonstrated that carp from the KSD-resistant AS strain and the susceptible Koi strain have similar total capacities to respond to stress. However, there were differences in the course of infection depending on the strain and temperature. Importantly, CEV infection activates the stress response, increasing serum cortisol and glucose levels, with a stronger effect at 18°C. CEV exhibits immunomodulatory properties by affecting the adaptive response of carp. Stress induced by CEV infection causes distinct changes in the gill and intestinal microbiomes, initiating secondary infections. CEV can also interact with other viral pathogens, exploiting them. For example, coinfection of fish with CEV and KHV or CEV and SVCV resulted in higher levels of CEV in the gills than infection with these viruses alone. Using OMICS (transcriptome, proteome, phosphoproteome, metabolome, and lipidome), we demonstrated the clear effects of infection, indicating pathological processes that lead to disease development and stress. Further, the detrimental effects of CEV on carp brains and testes have been demonstrated, explaining the detrimental effects on behavior and possible detrimental effects on reproductive success. Despite its strong immunomodulatory effects, CEV does not affect the efficacy of vaccines against other viruses, such as CyHV-3, and therefore does not influence vaccination success. Finally, it is important to note that carp that are naturally immunized show increased resistance to reinfection with CEV, which provides good prospects for developing a CEV vaccine. The project resulted in the publication of 14 peer-reviewed articles presenting original research results, as well as synthesizing existing and obtained knowledge in the form of reviews. By better understanding the interactions between the common carp and CEV and relating them to current knowledge about gill diseases in fish, we also identified avenues that could lead to the mitigation of disease burdens in the future, ensuring the better welfare of fish in aquaculture.

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