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Common carp (including ornamental koi carp) Cyprinus carpio L. are ecologically and economically important freshwater fish in Europe and Asia. C. carpio have recently been endangered by a third cyprinid herpesvirus, known as cyprinid herpesvirus-3 (CyHV-3), the etiological agent of koi herpesvirus disease (KHVD), which causes significant morbidity and mortality in koi and common carp. Clinical and pathological signs include epidermal abrasions, excess mucus production, necrosis of gill and internal organs, and lethargy. KHVD has decimated major carp populations in Israel,

Megalocytiviruses, such as infectious spleen and kidney necrosis virus (ISKNV), induce lethal systemic diseases in both ornamental and food fish species. In this study, we investigated an epizootic affecting Nile tilapia Oreochromis niloticus cultured in the US Midwest. Diseased fish displayed lethargy, gill pallor, and distension of the coelomic cavity due to ascites. Histopathological examination revealed a severe systemic abundance of intravascular megalocytes that were especially prominent in the gills, kidney, spleen, liver, and intestinal submucosa. Transmission electron microscopic examination revealed abundant intracytoplasmic polygonal virions consistent with iridovirus infection. Comparison of the full-length major capsid protein nucleotide sequences from a recent outbreak with a remarkably similar case that occurred at the same facility many years earlier revealed that both epizootics were caused by ISKNV. A comparison of this case with previous reports suggests that ISKNV may represent a greater threat to tilapia aquaculture than previously realized. KEY WORDS: Iridoviridae · Megalocytivirus · Infectious spleen and kidney necrosis virus · Aquaculture · Ornamental fish Resale or republication not permitted without written consent of the publisherDis Aquat Org 119: [253][254][255][256][257][258] 2016 Although tilapia are considered relatively resistant to disease, they are susceptible to common aquatic pathogens (e.g. viruses, bacteria, fungi, water molds, parasites) when reared intensively. The primary microbial pathogens affecting cultivated tilapia include Gram-negative bacteria (Aeromonas hydrophila, Flavobacterium columnare, and Francisella noatunensis), Gram-positive bacteria (Streptococcus spp.), and water molds such as members of the family Saprolegniaceae (e.g. Achyla and Saprolgenia spp.; Plumb & Hanson 2010). Despite the global culture of tilapia, few viruses have been described from tilapia, and none has proven to be a serious threat to the industry (El-Sayed 2006).The first RNA virus discovered in tilapia was an aquabirnavirus isolated from apparently healthy Mozambique tilapia O. mossambicus cultured in Lukang, Taiwan (Hedrick et al. 1983). In 2007, a betanodavirus was detected by RT-PCR in Nile tilapia larvae following a mass mortality event at a western European fish farm (Bigarré et al. 2009), andEyngor et al. (2014) isolated a novel RNA virus (tilapia lake virus) from wild tilapia and confirmed its pathogenicity via experimental infection in Nile tilapia.The first DNA viruses discovered in tilapia were iridoviruses. Although the family Iridoviridae is composed of 5 genera, only members of the genera Megalocytivirus, Lymphocystivirus, and Ranavirus infect fish (Zhang & Gui 2015). Paperna (1973) detected lymphocystis virus in tilapine and haplochromine cichlids from the Rift Valley Lakes Kitangiri and Victoria. A severe (100% mortality) epizootic among Mozambique tilapia fry held in an Australian aquatic disease laboratory was tentatively attributed to a ranavirus, Bohle ir...

Cyprinid herpesvirus-3 (CyHV-3) is an etiological agent of a notifiable disease that causes high mortality rates affecting both the common and koi carp Cyprinus carpio L. There is no current treatment strategy to save CyHV-3 infected fish. RNA mediated interference (RNAi) is an emerging strategy used for understanding gene function and is a promising method in developing novel therapeutics and antiviral medications. For this study, the possibility of activating the RNAi pathway by the use of small interfering (si)RNAs was tested to inhibit in vitro viral replication of CyHV-3 in common carp brain (CCB) cells. The siRNAs were designed to target either thymidine kinase (TK) or DNA polymerase (DP) genes, which both code for transcripts involved in DNA replication. The inhibition of viral replication caused by the siRNAs was measured by a reporter gene, termed ORF81. Treatment with siRNA targeting either TK or DP genes reduced the release of viral particles from infected CCB cells. However, siRNA targeting DP was most effective at reducing viral release as measured by qPCR.

Cyprinid herpesvirus 3 (CyHV-3) is the aetiological agent of a serious and notifiable disease afflicting common and koi carp, Cyprinus carpio L., termed koi herpesvirus disease (KHVD). Significant progress has been achieved in the last 15 years, since the initial reports surfaced from Germany, USA and Israel of the CyHV-3 virus, in terms of pathology and detection. However, relatively few studies have been carried out in understanding viral replication and propagation. Antibody-based affinity has been used for detection of CyHV-3 in enzyme-linked immunosorbent assay and PCR-based techniques, and immunohistological assays have been used to describe a CyHV-3 membrane protein, termed ORF81. In this study, monoclonal antibodies linked to Nhydroxysuccinimide (NHS)-activated spin columns were used to purify CyHV-3 and host proteins from tissue samples originating in either CyHV-3 symptomatic or asymptomatic fish. The samples were next analysed either by polyacrylamide gel electrophoresis (PAGE) and subsequently by electrospray ionization coupled to mass spectrometry (ESI-MS) or by ESI-MS analysis directly after purification. A total of 78 host proteins and five CyHV-3 proteins were identified in the two analyses. These data can be used to develop novel control methods for CyHV-3, based on pathways or proteins identified in this study.