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The common carp is one of the most economically valuable freshwater fish worldwide and its aquaculture can be severely affected by the koi sleepy disease (KSD)/carp edema virus disease (CEVD). This study explores a natural outbreak of CEVD in a pond containing both clinically healthy and diseased fish of various origins exposed to the virus. We investigated mRNA expression of genes associated with known antiviral immune mechanisms, such as type I interferon signalling and cell-mediated cytotoxicity, and performed a comprehensive protein expression analysis to highlight differences between the two groups in various organs. Significant differences in expression profiles of common carp with and without clinical signs were found to be strongly dependent on the organ from which the sample originated. Components of the complement cascade, including various C3 proteins, exhibited upregulation only in less affected organs, specifically the head kidney and spleen. Other complement proteins such as B/C2 and C9 showed upregulation in the kidney, spleen, and gills but not in the skin. Conversely, lysozymes C and G, were observed to be upregulated in the most affected organs of the skin and gills. This study submits the first description of the immune system related proteome using a mass spectrometry on the samples isolated from fish infected with CEV. It also offers a unique comparison of immune reaction of CEV infected and healthy fish under an infectious pressure., (© 2024 The Author(s). Journal of Fish Diseases published by John Wiley & Sons Ltd.)

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., (© 2024 The Authors. Journal of Fish Diseases published by John Wiley & Sons Ltd.)

The importance of world aquaculture production grows annually together with the increasing need to feed the global human population. Common carp (Cyprinus carpio) is one of the most important freshwater fish in global aquaculture. Unfortunately, carp production is affected by numerous diseases of which viral diseases are the most serious. Koi herpesvirus disease (KHVD), spring viraemia of carp (SVC), and during the last decades also koi sleepy disease (KSD) are currently the most harmful viral diseases of common carp. This review summarizes current knowledge about carp edema virus (CEV), aetiological agent causing KSD, and about the disease itself. Furthermore, the article is focused on summarizing the available information about the antiviral immune response of common carp, like production of class I interferons (IFNs), activation of cytotoxic cells, and production of antibodies by B cells focusing on anti-CEV immunity., (© 2021 John Wiley & Sons Ltd.)

Koi herpesvirus (KHV; cyprinid herpesvirus-3) and carp oedema virus (CEV) are important viruses of common and koi carp (Cyprinus carpio); however, the distribution of these viruses in wild common carp in North America is largely unknown. During the summers of 2017 and 2018, 27 mass mortalities of common carp were reported from four states in the USA (Minnesota, Iowa, Pennsylvania and Wisconsin), the majority of which were distributed across eight major watersheds in southern Minnesota. Samples from 22 of these mortality events and from five clinically healthy nearby carp populations were screened for KHV, CEV and SVCV using real-time polymerase chain reaction (qPCR). KHV was confirmed in 13 mortality events, CEV in two mortality events and coinfections of KHV/CEV in four mortality events. Nucleotide sequence analysis revealed that the KHV and CEV detected here are closely related to European lineages of these viruses. While molecular detection alone cannot conclusively link either virus with disease, the cases described here expand the known range of two important viruses. This is also the first reported detection of KHV and CEV coinfections in wild carp populations., (© 2019 John Wiley & Sons Ltd.)

Koi sleepy disease (KSD) is a disease with increasing importance in global common carp aquaculture. Despite the fact that carp edema virus (CEV) is most likely the causative agent of KSD, the disease often presents itself as multifactorial with several parasites and bacteria species present on gills, skin or in internal organs. Therefore, in this study, we analysed and presented initial results on an interaction of flavobacteria and CEV in the development of clinical KSD in carp suffering from proliferative gill disease. We examined selected field samples from Germany and Hungary and confirmed the presence of CEV and flavobacteria co-infections in subset of the samples. In several infection experiments, we studied the transfer and dynamics of both infections. Furthermore, we analysed which Flavobacterium species could be isolated from KSD-affected fish and concluded that Flavobacterium branchiophilum is a possible copathogen. Antibiotic treatment experiments showed that CEV seems to be the primary pathogen causing an insult to the gills of carp and by these enabling other pathogens, including F. branchiophilum, to establish co-infections. Despite the fact that F. branchiophilum co-infection is not required for the development of clinical KSD, it could contribute to the pathological changes recorded during the outbreaks., (© 2018 John Wiley & Sons Ltd.)

Hungary is an important carp producer with intensive trading relationships with farms in other carp-producing areas in Europe. Carp in Europe were recently found infected with carp edema virus (CEV), a poxvirus which causes the koi sleepy disease (KSD) syndrome. Moribund carp were collected from 17 fish farms and angling ponds in different regions of Hungary. Histological analysis of gills from these carp revealed a proliferation of the interlamellar epithelium and an infiltration by eosinophilic cells. In 13 of 17 of these carp, CEV DNA was detected by qPCR and in seven fish more than 1 × 10 4 copies of virus-specific DNA sequences per 250 ng of DNA, which could be considered as clinically relevant and a cause of disease. A phylogenetic analysis of the sequences revealed that all three genogroups of CEV were present in Hungarian common carp with genogroup I being most abundant. These results support the hypothesis of a prolonged presence of CEV in European carp populations and suggest that previous outbreaks of KSD were not recorded or misdiagnosed. Hence, a testing of carp and koi for infection with CEV should be included into disease surveillance programmes to prevent further spreading of this disease., (© 2017 John Wiley & Sons Ltd.)

Gill diseases cause considerable losses in Norwegian salmon farming. In 2015, we characterized salmon gill poxvirus (SGPV) and associated gill disease. Using newly developed diagnostic tools, we show here that SGPV infection is more widely distributed than previously assumed. We present seven cases of complex gill disease in Atlantic salmon farmed in seawater and freshwater from different parts of Norway. Apoptosis, the hallmark of acute SGPV infection, was not easily observed in these cases, and qPCR analysis was critical for identification of the presence of SGPV. Several other agents including Costia-like parasites, gill amoebas, Saprolegnia spp. and bacteria were observed. The studied populations experienced significant mortalities, which increased to extreme levels when severe SGPV infections coincided with smoltification. SGPV infection appears to affect the smoltification process directly by affecting the gills and chloride cells in particular. SGPV may be considered a primary pathogen as it was often found prior to identification of complex gill disease. It is hypothesized that SGPV-induced gill damage may impair innate immunity and allow invasion of secondary invaders. The distinct possibility that SGPV has been widely overlooked as a primary pathogen calls for extended use of SGPV qPCR in Atlantic salmon gill health management., (© 2017 John Wiley & Sons Ltd.)

Elucidation of the role of infectious agents putatively involved in gill disease is commonly hampered by the lack of culture systems for these organisms. In this study, a farmed population of Atlantic salmon pre-smolts, displaying proliferative gill disease with associated Candidatus Branchiomonas cysticola, Ca. Piscichlamydia salmonis and Atlantic salmon gill pox virus (SGPV) infections, was identified. A subpopulation of the diseased fish was used as a source of waterborne infection towards a population of naïve Atlantic salmon pre-smolts. Ca. B. cysticola infection became established in exposed naïve fish at high prevalence within the first month of exposure and the bacterial load increased over the study period. Ca. P. salmonis and SGPV infections were identified only at low prevalence in exposed fish during the trial. Although clinically healthy, at termination of the trial the exposed, naïve fish displayed histologically visible pathological changes typified by epithelial hyperplasia and subepithelial inflammation with associated bacterial inclusions, confirmed by fluorescent in situ hybridization to contain Ca. B. cysticola. The results strongly suggest that Ca. B. cysticola infections transmit directly from fish to fish and that the bacterium is directly associated with the pathological changes observed in the exposed, previously naïve fish., (© 2017 John Wiley & Sons Ltd.)

Fish samples initially collected by local veterinarians on the common and koi carp farms in Poland between 2013 and 2015 as part of a KHV surveillance programme, when the water temperature was between 16 and 26 °C, and were also tested for CEV by qPCR. A partial 478 nucleotide fragment of the 4a gene was subsequently generated from 17 qPCR-positive common carp Cyprinus carpio samples from 36 farm sites tested during the period. Sequence alignments and analysis revealed the presence of CEV in Poland both in common carp as well as in koi carp farms, and phylogenetic analysis assigned the Polish CEV sequences into three distinct genogroups. A lineage which includes the original sequences obtained from koi carp in Japan (genogroup II) included sequences from both koi carp and common carp, and the second lineage (genogroup I) contained sequences from common carp only. A third lineage (genogroup III) which was more closely related to the genogroup II also consisted of sequences from common carp only. The latter represents a lineage of CEV not previously described in the literature., (© 2016 John Wiley & Sons Ltd.)