Molecular characterization of the complete genome of falconid herpesvirus strain S-18

Characterization of a Unique Novel LORF3 Protein of Duck Plague Virus and Its Potential Pathogenesis

Duck plague virus (DPV) is a high-morbidity fowl alphaherpesvirus that causes septicemic lesions in various organs. Most DPV genes are conserved among herpesviruses, while a few are specific to fowl herpesviruses, including the LORF3 gene, for which there is currently no literature describing its biological properties and functions. This study first addressed whether the LORF3 protein is expressed by making specific polyclonal antibodies. We could demonstrate that DPV LORF3 is an early gene and encodes a protein involved in virion assembly, mainly localized in the nucleus of DPV-infected DEF cells. To investigate the role of this novel LORF3 protein in DPV pathogenesis, we generated a recombinant virus that lacks expression of the LORF3 protein. Our data revealed that the LORF3 protein is not essential for viral replication but contributes to DPV replication in vitro and in vivo and promotes duck plague disease morbidity and mortality. Interestingly, deletion of the LORF3 protein abolished thymus atrophy in DPV-vaccinated ducks. In conclusion, this study revealed the expression of avian herpesviruses-specific genes and unraveled the role of the early protein LORF3 in the pathogenesis of DPV. IMPORTANCE DPV is a highly lethal alphaherpesvirus that causes duck plague in birds of the order Anseriformes. The virus has caused huge economic losses to the poultry industry due to high morbidity and mortality and the cost of vaccination. DPV encodes 78 open reading frames (ORFs), and these genes are involved in various processes of the viral life cycle. Functional characterization of DPV genes is important for understanding the complex viral life cycle and DPV pathogenesis. Here, we identified a novel protein encoded by LORF3, and our data suggest that the LORF3 protein is involved in the occurrence and development of duck plague.

Detection of Herpesviruses in Wild Bird Casualties in Slovenia

The complete host range of avian herpesviruses in wild birds is unknown, and information about nucleotide sequences is available only in limited cases. The aim of this study was to detect the presence of herpesviruses in wild birds and to gain more information about their phylogenetic relationship. Oropharyngeal and cloacal swabs from 447 wild birds from 15 different orders presented as wildlife casualties were examined for herpesvirus presence with PCR targeting a fragment of the DNA polymerase gene. Herpesviruses were detected in oropharyngeal and/or cloacal swabs in 34 (7.5%) birds belonging to 11 species from six different avian orders: Accipitriformes, Charadriiformes, Columbiformes, Falconiformes, Passeriformes, and Strigiformes. The results of phylogenetic analysis showed that various herpesviruses sequences are present in the wild bird population. Some herpesviruses are host species–specific, whereas in some cases very similar sequences were detected through different avian orders, which confirms findings that herpesviruses are not always restricted to bird species. It seems that herpesvirus transmission could occur by predation from avian prey, and even by superpredation—for example, large owls, such as the Eurasian eagle owl (Bubo bubo) or Ural owl (Strix uralensis), preying on smaller raptors. This can lead to greater infection exposure and is in line with the fact that raptors were the most infected species group. Nevertheless, the individual or simultaneous detection of herpesviruses in oropharyngeal and cloacal swabs shows that both swab samples should be used for herpesvirus detection in wild birds.

Comparative Molecular Characterization of Three Gallid alphaherpesvirus Type 3 Strains 301B/1, HPRS24, and SB-1

Marek's disease (MD) is a highly contagious lymphoproliferative disease of chickens caused by Gallid alphaherpesvirus type 2. Gallid alphaherpesvirus type 3 (GaHV-3) strain 301B/1 was previously shown to be an effective MD vaccine with synergistic efficacy when used as a bivalent vaccine with turkey herpesvirus. Since the nucleotide sequences of only two GaHV-3 strains have been determined, we sought to sequence the 301B/1 genome using Illumina MiSeq technology. Phylogenomic analysis indicated that 301B/1 is more closely related to other GaHV-3 strains (SB-1 and HPRS24) than to virulent or attenuated strains of GaHV-2. One hundred and twenty-six open reading frames (ORFs) have been identified within the 301B/1 genome with 108 ORFs showing a high degree of similarity to homologs found in the genomes of SB-1 and HPRS24; 14 ORFs are highly homologous (> 90% identity) with the corresponding ORFs within the SB-1 genome. The R-LORF8 and R-LORF9 genes are the most dissimilar to the collinear genes found in the SB-1 genome but are highly homologous (99%-100% identity) with those within the HPRS24 genome. Overall the 301B/1 genome is most similar to the SB-1 virus genome (99.1%) and to a lesser degree with the HPRS24 virus genome (97.7%). However, six 301B/1 ORFs (UL47, UL48, UL52, pp38, ICP4, and US10) have been identified that contain nonsynonymous substitutions relative to homologs found in the SB-1 genome. Notably, unlike the avian retrovirus long terminal repeat sequences found within the SB-1 genome, none were identified within the 301B/1 genome.

Inclusion Body Herpesvirus Hepatitis in Captive Falcons in the Middle East: A Review of Clinical and Pathologic Findings

Inclusion body hepatitis in falcons is caused by a herpesvirus designated Falconid HV-1. This herpesvirus and other herpesviruses affecting birds of prey have not been assigned to a genus and include inclusion body herpesvirus hepatitis in eagles (Accipitrid HV-1) and inclusion body herpesvirus hepatitis in owls (Strigid HV-1). Herpesvirus infections have been diagnosed in both captive and free-living raptors across Europe, North America, and Asia in different species of the family Falconidae. Herpesviruses affecting owls and falcons have been found to be antigenically similar to pigeon herpesvirus (Columbid HV-1) and distinct from other avian herpesviruses. When the herpesvirus isolates from owls, falcons, and pigeons were compared by sequencing a fragment of the herpes viral DNA polymerase gene from those birds naturally infected with the virus, the sequences from these 3 sources were found to be nearly identical. The authors of this study concluded that the Falconid HV-1, Strigid HV-1, and Columbid HV-1 were the same virus. Furthermore, the authors also proposed that the virus therefore be referred to as Columbid HV-1 (CoHV-1), because pigeons may be responsible for the transmission of the virus to birds of prey. Pigeons are often carriers of the virus without showing any clinical signs. It has long been suspected that raptors may contract the infection by the ingestion of infected pigeons. Some studies have suggested that falcons may not contract the infection through the oral route by ingesting carrier pigeons, but through the ocular or nasal route. Inclusion body herpesvirus hepatitis is a frequently diagnosed disease in the captive falcon population used for falconry, racing, and breeding in the Middle East, and it seems to be associated with the extensive use of pigeons for training and as a food item. This paper reviews the clinical and pathological findings in falcons affected by inclusion body herpesvirus hepatitis in the Middle East.

Detection and Phylogenetic Analysis of Herpesviruses Detected in Wild Owls in Slovenia

Herpesvirus (HV) was detected using PCR in the organs of eight of 55 wild owls (14.5%) from seven species that were found dead in various locations in Slovenia between 1995 and 2015. HV was detected in three species: the Eurasian eagle owl (Bubo bubo), Ural owl (Strix uralensis), and long-eared owl (Asio otus). Phylogenetic analysis of partial DNA polymerase gene nucleotide sequences showed that the detected HVs are similar to the avian and mammal alphaherpesviruses. Two sequences were very similar to known bird HV sequences. One sequence was identical to the columbid herpesvirus 1 (CoHV1) sequence, and the other was very similar to the gallid herpesvirus 2 (GaHV2) sequence. The phylogenetic tree revealed a lower similarity of the other six analyzed Slovenian sequences with the sequences of alphaherpesviruses of birds and mammals. This is the first study to report the detection of different HVs in owls.

The ORF012 gene of Marek's disease virus type 1 produces a spliced transcript and encodes a novel nuclear phosphoprotein essential for virus growth

Marek's disease virus (MDV), an alphaherpesvirus, is the causative agent of a lethal disease in chickens characterized by generalized nerve inflammation and rapid lymphoma development. The extensive colinearity of the MDV genome with those of related herpesviruses has eased functional characterization of many MDV genes. However, MDV carries a number of unique open reading frames (ORFs) that have not yet been investigated regarding their coding potentials and the functions of their products. Among these unique ORFs are two putative ORFs, ORF011 and ORF012, which are found at the extreme left end of the MDV unique long region. Using reverse transcriptase PCR, we showed that ORF011 and ORF012 are not individual genes but form a single gene through mRNA splicing of a small intron, resulting in the novel ORF012. We generated an ORF012-null virus using an infectious clone of MDV strain RB-1B. The deletion virus had a marked growth defect in vitro and could not be passaged in cultured cells, suggesting an essential role for the ORF012 product in virus replication. Further studies revealed that protein 012 (p012) localized to the nucleus in transfected and infected cells, and we identified by site-directed mutagenesis and green fluorescent protein (GFP) reporter fusion assays a nuclear localization signal (NLS) that was mapped to a 23-amino-acid sequence at the protein's C terminus. Nuclear export was blocked using leptomycin B, suggesting a potential role for p012 as a nuclear/cytoplasmic shuttling protein. Finally, p012 is phosphorylated at multiple residues, a modification that could possibly regulate its subcellular distribution.

IMPORTANCE

Marek's disease virus (MDV) causes a devastating oncogenic disease in chickens with high morbidity and mortality. The costs for disease prevention reach several billion dollars annually. The functional investigation of MDV genes is necessary to understand its complex replication cycle, which eventually could help us to interfere with MDV and herpesviral pathogenesis. We have identified a previously unidentified phosphoprotein encoded by MDV ORF012. We were able to show experimentally that predicted splicing of the gene based on bioinformatics data does indeed occur during replication. The newly identified p012 is essential for MDV replication and localizes to the nucleus due to the presence of a transferable nuclear localization signal at its C terminus. Our results also imply that p012 could constitute a nucleocytoplasmic shuttle protein, a feature that could prove interesting and important.