Eel herpesvirus or anguillid herpesvirus 1 (AngHV1) frequently causes disease in freshwater eels. The complete genome sequence of AngHV1 and its taxonomic position within the family Alloherpesviridae were determined. Shotgun sequencing revealed a 249 kbp genome including an 11 kbp terminal direct repeat that contains 7 of the 136 predicted protein-coding open reading frames. Twelve of these genes are conserved among other members of the family Alloherpesviridae and another 28 genes have clear homologues in cyprinid herpesvirus 3. Phylogenetic analyses based on amino acid sequences of five conserved genes, including the ATPase subunit of the terminase, confirm the position of AngHV1 within the family Alloherpesviridae, where it is most closely related to the cyprinid herpesviruses. Our analyses support a recent proposal to subdivide the family Alloherpesviridae into two sister clades, one containing AngHV1 and the cyprinid herpesviruses and the other containing Ictalurid herpesvirus 1 and the ranid herpesviruses.One of the commonly observed and economically most relevant viruses in wild and cultured freshwater eels of the genus Anguilla is anguillid herpesvirus 1 (AngHV1) (Haenen et al., 2002;van Ginneken et al., 2004), also known as eel herpesvirus and herpesvirus anguillae (Sano et al., 1990). Other formerly used names include eel herpesvirus in Formosa (Ueno et al., 1992(Ueno et al., , 1996, gill herpesvirus of eel (Lee et al., 1999) and European eel herpesvirus (Chang et al., 2002). AngHV1 was first isolated from cultured European eels (Anguilla anguilla) and Japanese eels (Anguilla japonica) in Japan in 1985(Sano et al., 1990. Several herpesviral disease outbreaks in Japanese eels (Kobayashi & Miyazaki, 1997;Lee et al., 1999;Ueno et al., 1992) and European eels (Chang et al., 2002; Davidse et al., 1999;Haenen et al., 2002;Jakob et al., 2009;van Ginneken et al., 2004) have since been reported. Serological, molecular and sequence data indicated that the Asian and European eel herpesvirus isolates can be considered as a single virus species (Chang et al., 2002;Rijsewijk et al., 2005; Waltzek et al., 2009). Clinical and pathological findings of the infection vary among and within outbreaks but characteristically include haemorrhages in skin, fins, gills and liver, and a significantly increased mortality (Chang et al., 2002; Davidse et al., 1999;Haenen et al., 2002;Kobayashi & Miyazaki, 1997;Sano et al., 1990;Ueno et al., 1992;van Ginneken et al., 2004).Herpesviruses are large and complex linear double-stranded DNA viruses with a distinctive morphology . Accordingly, AngHV1 virions consist of a core, an icosahedral nucleocapsid made up of hollow capsomers (T516) with a diameter of about 110 nm, a proteinaceous tegument, and a host-derived envelope with a diameter of about 200 nm containing virus-encoded glycoproteins (Davidse et al., 1999;Sano et al., 1990). At the genome sequence level, only a single gene, encoding the putative ATPase subunit of the terminase (hereafter terminase), is convincingly conserved amo...

Avian coronaviruses of the genus Gammacoronavirus are represented by infectious bronchitis virus (IBV), the coronavirus of chicken. IBV causes a highly contagious disease affecting the respiratory tract and, depending on the strain, other tissues including the reproductive and urogenital tract. The control of IBV in the field is hampered by the many different strains circulating worldwide and the limited protection across strains due to serotype diversity. This diversity is believed to be due to the amino acid variation in the S1 domain of the major viral attachment protein spike. In the last years, much effort has been undertaken to address the role of the avian coronavirus spike protein in the various steps of the virus' live cycle. Various models have successfully been developed to elucidate the contribution of the spike in binding of the virus to cells, entry of cell culture cells and organ explants, and the in vivo tropism and pathogenesis. This review will give an overview of the literature on avian coronavirus spike proteins with particular focus on our recent studies on binding of recombinant soluble spike protein to chicken tissues. With this, we aim to summarize the current understanding on the avian coronavirus spike's contribution to host and tissue predilections, pathogenesis, as well as its role in therapeutic and protective interventions.

Many viruses have evolved strategies to deregulate the host immune system. These strategies include mechanisms to subvert or recruit the host cytokine network. IL-10 is a pleiotropic cytokine that has both immunostimulatory and immunosuppressive properties. However, its key features relate mainly to its capacity to exert potent immunosuppressive effects. Several viruses have been shown to upregulate the expression of cellular IL-10 (cIL-10) with, in some cases, enhancement of infection by suppression of immune functions. Other viruses encode functional orthologues of cIL-10, called viral IL-10s (vIL-10s). The present review is devoted to these virokines. To date, vIL-10 orthologues have been reported for 12 members of the family Herpesviridae, two members of the family Alloherpesviridae and seven members of the family Poxviridae. Study of vIL-10s demonstrated several interesting aspects on the origin and the evolution of these viral genes, e.g. the existence of multiple (potentially up to nine) independent gene acquisition events at different times during evolution, viral gene acquisition resulting from recombination with cellular genomic DNA or cDNA derived from cellular mRNA and the evolution of cellular sequence in the viral genome to restrict the biological activities of the viral orthologues to those beneficial for the virus life cycle. Here, various aspects of the vIL-10s described to date are reviewed, including their genetic organization, protein structure, origin, evolution, biological properties and potential in applied research. IL-10 is a pleiotropic cytokine, with both immunostimulatory and immunosuppressive properties (Moore et al., 2001). However, its key features relate mainly to its capacity to exert potent effects in the latter category via several mechanisms. Various viruses have been shown to upregulate the expression of cellular IL-10 (cIL-10) with, in some cases, an enhancement of infection by suppression of immune functions (

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BackgroundAvian coronavirus infectious bronchitis virus (IBV) is a respiratory pathogen of chickens that causes severe economic losses in the poultry industry worldwide. Major advances in the study of the molecular biology of IBV have resulted from the development of reverse genetics systems for the highly attenuated, cell culture-adapted, IBV strain Beaudette. However, most IBV strains, amongst them virulent field isolates, can only be propagated in embryonated chicken eggs, and not in continuous cell lines.MethodsWe established a reverse genetics system for the IBV strain H52, based on targeted RNA recombination in a two-step process. First, a genomic and a chimeric synthetic, modified IBV RNA were co-transfected into non-susceptible cells to generate a recombinant chimeric murinized (m) IBV intermediate (mIBV). Herein, the genomic part coding for the spike glycoprotein ectodomain was replaced by that of the coronavirus mouse hepatitis virus (MHV), allowing for the selection and propagation of recombinant mIBV in murine cells. In the second step, mIBV was used as the recipient. To this end a recombination with synthetic RNA comprising the 3′-end of the IBV genome was performed by introducing the complete IBV spike gene, allowing for the rescue and selection of candidate recombinants in embryonated chicken eggs.ResultsTargeted RNA recombination allowed for the modification of the 3′-end of the IBV genome, encoding all structural and accessory genes. A wild-type recombinant IBV was constructed, containing several synonymous marker mutations. The in ovo growth kinetics and in vivo characteristics of the recombinant virus were similar to those of the parental IBV strain H52.ConclusionsTargeted RNA recombination allows for the generation of recombinant IBV strains that are not able to infect and propagate in continuous cell lines. The ability to introduce specific mutations holds promise for the development of rationally designed live-attenuated IBV vaccines and for studies into the biology of IBV in general.Electronic supplementary materialThe online version of this article (doi:10.1186/s12985-017-0775-8) contains supplementary material, which is available to authorized users.

Many of the known fish herpesviruses have important aquaculture species as their natural host, and may cause serious disease and mortality. Anguillid herpesvirus 1 (AngHV-1) causes a hemorrhagic disease in European eel, Anguilla anguilla. Despite their importance, fundamental molecular knowledge on fish herpesviruses is still limited. In this study we describe the identification and localization of the structural proteins of AngHV-1. Purified virions were fractionated into a capsid-tegument and an envelope fraction, and premature capsids were isolated from infected cells. Proteins were extracted by different methods and identified by mass spectrometry. A total of 40 structural proteins were identified, of which 7 could be assigned to the capsid, 11 to the envelope, and 22 to the tegument. The identification and localization of these proteins allowed functional predictions. Our findings include the identification of the putative capsid triplex protein 1, the predominant tegument protein, and the major antigenic envelope proteins. Eighteen of the 40 AngHV-1 structural proteins had sequence homologues in related Cyprinid herpesvirus 3 (CyHV-3). Conservation of fish herpesvirus structural genes seemed to be high for the capsid proteins, limited for the tegument proteins, and low for the envelope proteins. The identification and localization of the structural proteins of AngHV-1 in this study adds to the fundamental knowledge of members of the Alloherpesviridae family, especially of the Cyprinivirus genus.

Avian coronavirus infectious bronchitis virus (IBV) infects domestic fowl, resulting in respiratory disease and causing serious losses in unprotected birds. Its control is mainly achieved by using live attenuated vaccines. Here we explored the possibilities for rationally attenuating IBV to improve our knowledge regarding the function of IBV accessory proteins and for the development of next-generation vaccines with the recently established reverse genetic system for IBV H52 based on targeted RNA recombination and selection of recombinant viruses in embryonated eggs. To this aim, we selectively removed accessory genes 3a, 3b, 5a and 5b individually, and rescued the resulting recombinant (r) rIBV-Δ3a, rIBV-Δ3b, rIBV-Δ5a and rIBV-Δ5b. In vitro inoculation of chicken embryo kidney cells with recombinant and wild-type viruses demonstrated that the accessory protein 5b is involved in the delayed activation of the interferon response of the host after IBV infection. Embryo mortality after the inoculation of 8-day-old embryonated chicken eggs with recombinant and wild-type viruses showed that rIBV-Δ3b, rIBV-Δ5a and rIBV-Δ5b had an attenuated phenotype in ovo, with reduced titres at 6 h p.i. and 12 h p.i. for all viruses, while growing to the same titre as wild-type rIBV at 48 h p.i. When administered to 1-day-old chickens, rIBV-Δ3a, rIBV-Δ3b, rIBV-Δ5a and rIBV-Δ5b showed reduced ciliostasis in comparison to the wild-type viruses. In conclusion, individual deletion of accessory genes in IBV H52 resulted in mutant viruses with an attenuated phenotype.

Viruses exploit molecules on the target membrane as receptors for attachment and entry into host cells. Thus, receptor expression patterns can define viral tissue tropism and might to some extent predict the susceptibility of a host to a particular virus. Previously, others and we have shown that respiratory pathogens of the genus Gammacoronavirus, including chicken infectious bronchitis virus (IBV), require specific ␣2,3-linked sialylated glycans for attachment and entry. Here, we studied determinants of binding of enterotropic avian gammacoronaviruses, including turkey coronavirus (TCoV), guineafowl coronavirus (GfCoV), and quail coronavirus (QCoV), which are evolutionarily distant from respiratory avian coronaviruses based on the viral attachment protein spike (S1). We profiled the binding of recombinantly expressed S1 proteins of TCoV, GfCoV, and QCoV to tissues of their respective hosts. Protein histochemistry showed that the tissue binding specificity of S1 proteins of turkey, quail, and guineafowl CoVs was limited to intestinal tissues of each particular host, in accordance with the reported pathogenicity of these viruses in vivo. Glycan array analyses revealed that, in contrast to the S1 protein of IBV, S1 proteins of enteric gammacoronaviruses recognize a unique set of nonsialylated type 2 poly-N-acetyl-lactosamines. Lectin histochemistry as well as tissue binding patterns of TCoV S1 further indicated that these complex N-glycans are prominently expressed on the intestinal tract of various avian species. In conclusion, our data demonstrate not only that enteric gammacoronaviruses recognize a novel glycan receptor but also that enterotropism may be correlated with the high specificity of spike proteins for such glycans expressed in the intestines of the avian host. IMPORTANCEAvian coronaviruses are economically important viruses for the poultry industry. While infectious bronchitis virus (IBV), a respiratory pathogen of chickens, is rather well known, other viruses of the genus Gammacoronavirus, including those causing enteric disease, are hardly studied. In turkey, guineafowl, and quail, coronaviruses have been reported to be the major causative agent of enteric diseases. Specifically, turkey coronavirus outbreaks have been reported in North America, Europe, and Australia for several decades. Recently, a gammacoronavirus was isolated from guineafowl with fulminating disease. To date, it is not clear why these avian coronaviruses are enteropathogenic, whereas other closely related avian coronaviruses like IBV cause respiratory disease. A comprehensive understanding of the tropism and pathogenicity of these viruses explained by their receptor specificity and receptor expression on tissues was therefore needed. Here, we identify a novel glycan receptor for enteric avian coronaviruses, which will further support the development of vaccines.