The growth of duck hepatitis virus in ducklings

The growth patterns of the Houchin strain of duck hepatitis virus in different tissues of ducklings infected when 11 days old were similar but their magnitudes and the times at which virus growth occurred differed significantly. The virus multiplied best in the liver and less well in kidneys, spleen, small and large intestines, and pancreas. Virus present in bile was attributable to virus excreted from the liver. Virus in other tissues was attributable to the virus content of blood. Virus was recovered from cloacal swabs taken from infected ducklings from 24 hours after exposure and excretion continued for a further 11 days.Age -related resistance to duck virus hepatitis was manifested in ducklings by a decline in the mortality rate as the birds grew older and was linked to a lengthening of the lag phase of virus growth, to a steady depression of virus growth, and to a shortening in the period of virus excretion. Multiplication rates of the virus, however, were not affected.An age- related resistance was found also in chicken embryos and duck embryos infected with the Houchin strain of duck hepatitis virus. A strain, H56, adapted to chicken embryos by serial passages overcame this age -related resistance in chicken embryos

A proposed disease classification system for duck viral hepatitis

The nomenclature of duck viral hepatitis (DVH) was historically not a problem. However, 14 hepatotropic viruses among 10 different genera are associated with the same disease name, DVH. Therefore, the disease name increasingly lacks clarity and may no longer fit the scientific description of the disease. Because one disease should not be attributed to 10 genera of viruses, this almost certainly causes misunderstanding regarding the disease-virus relationship. Herein, we revisited the problem and proposed an update to DVH disease classification. This classification is based on the nomenclature of human viral hepatitis and the key principle of Koch's postulates (“one microbe and one disease”). In total, 10 types of disease names have been proposed. These names were literately matched with hepatitis-related viruses. We envision that this intuitive nomenclature system will facilitate scientific communication and consistent interpretation in this field, especially in the Asian veterinary community, where these diseases are most commonly reported

The duck hepatitis virus 5'-UTR possesses HCV-like IRES activity that is independent of eIF4F complex and modulated by downstream coding sequences

Duck hepatitis virus (DHV-1) is a worldwide distributed picornavirus that causes acute and fatal disease in young ducklings. Recently, the complete genome of DHV-1 has been determined and comparative sequence analysis has shown that possesses the typical picornavirus organization but exhibits several unique features. For the first time, we provide evidence that the 626-nucleotide-long 5'-UTR of the DHV-1 genome contains an internal ribosome entry site (IRES) element that functions efficiently both in vitro and in mammalian cells. The prediction of the secondary structure of the DHV-1 IRES shows significant similarity to the hepatitis C virus (HCV) IRES. Moreover, similarly to HCV IRES, DHV-1 IRES can direct translation initiation in the absence of a functional eIF4F complex. We also demonstrate that the activity of the DHV-1 IRES is modulated by a viral coding sequence located downstream of the DHV-1 5'-UTR, which enhances DHV-1 IRES activity both in vitro and in vivo. Furthermore, mutational analysis of the predicted pseudo-knot structures at the 3'-end of the putative DHV-1 IRES supported the presence of conserved domains II and III and, as it has been previously described for other picornaviruses, these structures are essential for keeping the normal internal initiation of translation of DHV-1

Occurrence, function and evolutionary origins of ‘2A-like’ sequences in virus genomes

2A is an oligopeptide sequence mediating a ribosome ‘skipping’ effect, producing an apparent ‘cleavage’ of polyproteins. First identified and characterized in picornaviruses, ‘2A-like’ sequences are found in other mammalian viruses and a wide range of insect viruses. Databases were analysed using a motif conserved amongst 2A/2A-like sequences. The newly identified 2A-like sequences (30 aa) were inserted into a reporter polyprotein to determine their cleavage activity. Our analyses showed that these sequences fall into two categories. The majority mediated very high (complete) cleavage to separate proteins and a few sequences mediated cleavage with lower efficiency, generating appreciable levels of the uncleaved form. Phylogenetic analyses of 2A-like sequences and RNA-dependent RNA polymerases (RdRps) indicated multiple, independent, acquisitions of these sequences at different stages during virus evolution. Within a virus family, 2A sequences are (probably) homologous, but diverge due to other evolutionary pressures. Amongst different families, however, 2A/2A-like sequences appear to be homoplasic

Serendipitous identification of a new Iflavirus-like virus infecting tomato and its subsequent characterization

The genomic sequence of a previously undescribed virus was identified from symptomless tomato plants (Solanum lycopersicum). The viral genome is a positive-sense ssRNA molecule of 8506 nucleotides. It is predicted to encode a single polyprotein of 314·5 kDa that is subsequently processed into three coat protein components of 13·7, 17·9 and 13·5 kDa, and a viral replicase of approximately 207 kDa with conserved motifs for a helicase, a protease and RNA-dependent RNA polymerase (RdRp). Pairwise analysis of the deduced amino acid sequence of the RdRp revealed that it shares closest identity with members of the family Iflaviridae, genus Iflavirus (19–47% identity). Evidence of replication in plants was detected by RT-PCR of the viral replicative strand, and short interfering RNAs (siRNAs) matching the virus. The name Tomato matilda virus (TMaV) is proposed, and furthermore, that the genus Tomavirus (Tomato matilda virus) be created within the family Iflaviridae. This is the first report of a plant-infecting virus resembling members of the Iflaviridae

Establishing a TaqMan-Based Real-Time PCR Assay for the rapid detection and quantification of the newly emerged duck tembusu virus

To establish an accurate, rapid, and a quantifiable method for the detection of the newly emerged duck Tembusu virus (DTMUV) that recently caused a widespread infectious disease in ducks in China, we developed a TaqMan-based real-time PCR assay by using E gene-specific primers and a TaqMan probe. This real-time PCR assay was 100 times more sensitive than the conventional PCR. The reproducibility and specificity of the real-time PCR assay were confirmed using plasmids containing E genes or RNAs and DNAs extracted from well-known viruses causing duck diseases. The reliability of this real-time PCR assay was confirmed in 19 of the 24 swab samples, 22 of the 24 tissue samples collected from experimentally infected ducks, as well as 15 of the 21 clinical samples collected from sick ducks since they were verified as DTMUV-positive. The results reveal that the newly established real-time PCR assay might be a useful diagnostic method for epidemiologically investigating and closely observing the newly emerged DTMUV

Novel picornavirus in turkey poults with hepatitis, California, USA

To identify a candidate etiologic agent for turkey viral hepatitis, we analyzed samples from diseased turkey poults from 8 commercial flocks in California, USA, that were collected during 2008–2010. High-throughput pyrosequencing of RNA from livers of poults with turkey viral hepatitis (TVH) revealed picornavirus sequences. Subsequent cloning of the ≈9-kb genome showed an organization similar to that of picornaviruses with conservation of motifs within the P1, P2, and P3 genome regions, but also unique features, including a 1.2-kb sequence of unknown function at the junction of P1 and P2 regions. Real-time PCR confirmed viral RNA in liver, bile, intestine, serum, and cloacal swab specimens from diseased poults. Analysis of liver by in situ hybridization with viral probes and immunohistochemical testing of serum demonstrated viral nucleic acid and protein in livers of diseased poults. Molecular, anatomic, and immunologic evidence suggests that TVH is caused by a novel picornavirus, tentatively named turkey hepatitis virus