ICTV virus taxonomy profile: Birnaviridae.

Birnaviridae is a family of viruses with bi-segmented dsRNA genomes totalling about 6 kbp forming icosahedral, non-enveloped virions. The family includes four genera, members of three of which (Aquabirnavirus, Avibirnavirus and Blosnavirus) infect vertebrates (excluding mammals), whereas members of the fourth genus (Entomobirnavirus) infect insects. Each genus includes 1-3 species. Infectious pancreatic necrosis virus of salmonids and infectious bursal disease virus of poultry are two economically important birnaviruses. This is a summary of the International Committee on Taxonomy of Viruses (ICTV) Report on the taxonomy of Birnaviridae, which is available at www.ictv.global/report/birnaviridae.

Electron microscopic identification of viruses associated with poult enteritis in turkeys grown in California 1993-2003.

Poult enteritis (PE) is one of the most common diseases seen in young turkey flocks. Since 1993, more than 1800 cases of suspected PE have been submitted for examination by negative stain electron microscopy; this has involved more than 2400 individual results, because in many cases more than one virus was identified; at least 1500 individual results were positive for viruses. Viruses have been identified in poults as young as 3 days and up to 9 wk of age. The most commonly found viruses are rotavirus-like viruses and small round viruses ranging from 15 nm to 30 nm, either alone or in combination. Reovirus, birnavirus, and adenovirus have also been detected. There has been no evidence to suggest the presence of coronaviruses. This report summarizes our findings.

Structure of birnavirus-like particles determined by combined electron cryomicroscopy and X-ray crystallography.

Birnaviruses possess a capsid with a single protein layer in contrast to most double-stranded RNA viruses infecting multicellular eukaryotes. Using freeze-drying and heavy metal shadowing, the capsids of two birnaviruses, infectious bursal disease virus (IBDV) and infectious pancreatic necrosis virus, as well as of an IBDV virus-like particle (VLP) are shown to follow the same T=13 laevo icosahedral geometry. The structure of the VLP was determined at a resolution of approximately 15 A (1.5 nm) by a combination of electron cryomicroscopy and a recently developed three-dimensional reconstruction method, where the scattering density is expressed in terms of symmetry-adapted functions. This reconstruction methodology is well adapted to the icosahedral symmetry of viruses and only requires a small number of images to analyse. The atomic model of the external capsid protein, VP2, recently determined by X-ray crystallography, fits well into the VLP reconstruction and occupies all the electron densities present in the map. Thus, similarly to the IBDV virion, only VP2 forms the icosahedral layer of the VLP. The other components of both VLP and IBDV particles that play a crucial role in the capsid assembly, VP1, VP3 and the peptides arising from the processing of pVP2, do not follow the icosahedral symmetry, allowing them to be involved in other processes such as RNA packaging.

First isolation of an aquatic birnavirus from farmed and wild fish species in Australia.

During routine sampling and testing, as part of a systematic surveillance program (the Tasmanian Salmonid Health Surveillance Program), an aquatic birnavirus was isolated from 'pin-head' (fish exhibiting deficient acclimatisation on transfer to saltwater) Atlantic salmon Salmo salar, approximately 18 mo old, farmed in net-pens located in Macquarie Harbour on the west coast of Tasmania, Australia. The isolate grows readily in a range of fish cell lines including CHSE-214, RTG-2 and BF-2 and is neutralised by a pan-specific rabbit antiserum raised against infectious pancreatic necrosis virus (IPNV) Ab strain and by a commercial pan-specific IPNV-neutralising monoclonal antibody. Presence of the virus was not associated with gross clinical signs. Histopathological examination revealed a range of lesions particularly in pancreatic tissue. The virus was localised in pancreas sections by immunoperoxidase staining using the polyclonal antiserum and by electron microscopy. Examination by electron microscopy demonstrated that the virus isolated in cell culture (1) belongs to the family Birnaviridae, genus Aquabirnaviridae; (2) was ultrastructurally and antigenically similar to virus identified in the index fish; (3) is related to IPNV. Western blot analysis using the polyclonal rabbit antiserum confirmed the cross-reactions between various aquatic birnavirus isolates. In addition, PCR analysis of isolated viral nucleic acid from the index case indicated that the virus is more closely related to IPNV fr21 and N1 isolates than to other birnavirus isolates available for comparison. Sampling of other fish species within Macquarie Harbour has demonstrated that the virus is present in several other species of fish including farmed rainbow trout Oncorhynchus mykiss, wild flounder Rhombosolea tapirina, cod Pseudophycis sp., spiked dogfish Squalus megalops and ling Genypterus blacodes.

Characteristics of a new birnavirus associated with a warm-water fish cell line.

A warm-water fish cell line developed from blotched snakehead caudal peduncle (BSN) was found to have persistent birnavirus infection. Purified virus particles were of icosahedral shape and had 57+/-1.6 nm diameter. The BSN virus was resistant to 5-iodo-2'-deoxyuridine and induced yellowish-green cytoplasmic inclusions when stained with acridine orange. The virus was resistant to chloroform, acid and alkaline pH and heat treatment at 56 degrees C for 2 h. Purified virions had a buoyant density of 1.33 g/ml in CsCl and contained two genomic segments with molecular masses of 2.56 x 10(6) and 2.00 x 10(6) Da and four structural polypeptides of 112 (polyprotein, PP), 91 (VP1), 44 (VP2) and 37 (VP3) kDa. Reciprocal beta cross-neutralization tests incorporating four classical strains of infectious pancreatic necrosis virus (IPNV) (WB, Sp, Ab and TV-1) and the BSN virus established the complete serological distinctness of the virus from IPNV. Considering the uniqueness of the virus, the name blotched snakehead virus is proposed for this agent.

Major viral diseases affecting fish aquaculture in Spain.

The number of viruses isolated from fish has grown in the last few years as a reflection of the increasing interest in fish diseases, particularly those occurring in aquaculture facilities. Of all the described viruses, only a few are considered to be of serious concern and economic importance; they are described in this review, drawing special attention to the four families of viruses (Birnaviridae, Rhabdoviridae, Iridoviridae and Reoviridae) that have been reported in Spanish aquaculture. Infectious pancreatic necrosis virus, a member of the first family, is the most spread virus with a prevalence of 39%. Viral diseases are untreatable and because effective and safe vaccines for fish are not yet commercially available, a great care needs to be exercised when moving fish or eggs from one site or country to another. Some fish health control regulations have been legislated in Europe and USA.