Transcript mapping of the ‘early’ genes of Orf virus

Temporal and spatial characterization of keratinocytes supporting orf virus replication

Reflecting their tropism for keratinocytes, most poxviruses that infect vertebrates replicate to high titers and cause pathology in the skin. Keratinocytes, the main cells of the epidermis, are found in different stages of a differentiation program that produces the critical barrier against environmental damage. While systemic poxviruses (e.g. smallpox virus, sheeppox virus) also infect other cell types, the parapoxvirus orf virus (ORFV), which causes localized infections in sheep and goats, has not been shown to replicate in cells other than keratinocytes. Notably, ORFV infection only occurs after or concomitant with epidermal damage and the subsequent healing response and shows unexplained delayed virus replication in an uncharacterized keratinocyte subpopulation. Using in situ hybridization, immunohistochemistry, confocal microscopy, qPCR, and a full-thickness wound/infection model in sheep, the natural host, we show that during an initial 2-day eclipse phase viral transcription and viral DNA replication are not detected. Between days 2 and 3 pi, viral transcription is first detected in keratinocytes of the stratum granulosum and upper stratum spinosum in the proliferative zone at the wound margin. These cells are positive for cytokeratin 10, a suprabasal marker; cytokeratin 6, a protein induced during early repair responses; stratum granulosum markers filaggrin and loricrin; and negative for the nuclear proliferation marker Ki-67 and cytokeratin 14, a basal cell marker. This marker profile suggests that keratinocytes supportive of viral replication are engaged in advanced keratinocyte differentiation rather than proliferation.

Host factor cyclophilin B affects Orf virus replication by interacting with viral ORF058 protein

Poxviruses have evolved multiple strategies to modulate host-derived factors to create an optimal environment for viral efficient replication. Our previous study indicated that cyclophilin B (CypB) is a critical factor for ORFV replication in MDBK cells. However, the precise molecular mechanism by which CypB facilitates ORFV replication remains less understood. In the present study, the function of CypB in ORFV replication is further evaluated. The overexpression of CypB was observed to facilitate ORFV replication in OFTu cells and HeLa cells, however, RNA interference (RNAi)-mediated reduction of endogenous CypB decreased the levels of ORFV replication. Coimmunoprecipitation experiments revealed that the CypB interacted with ORFV ORF058 protein, a late protein involved in virus entry. The interaction of host factor CypB and ORF058 protein was further confirmed by confocal microscopy analysis and GST-pull down. In addition, the 52-55 aa was identified as the critical binding sites for CypB on ORF058 protein by GST-pull down with OFTu cells overexpressing CypB and purified GST-tagged truncated ORF058. In conclusion, we demonstrate that CypB is a critical host factor for ORFV replication in vitro by interacting with ORF058 protein, providing new insights into ORFV pathogenesis.

Orf virus (ORFV) infection in a three-dimensional human skin model: Characteristic cellular alterations and interference with keratinocyte differentiation

ORF virus (ORFV) is the causative agent of contagious ecthyma, a pustular dermatitis of small ruminants and humans. Even though the development of lesions caused by ORFV was extensively studied in animals, only limited knowledge exists about the lesion development in human skin. The aim of the present study was to evaluate a three-dimensional (3D) organotypic culture (OTC) as a human skin model for ORFV infection considering lesion development, replication of the virus, viral gene transcription and modulation of differentiation of human keratinocytes by ORFV. ORFV infection of OTC was performed using the ORFV isolate B029 derived from a human patient. The OTC sections showed a similar structure of stratified epidermal keratinocytes as human foreskin and a similar expression profile of the differentiation markers keratin 1 (K1), K10, and loricrin. Upon ORFV infection, OTCs exhibited histological cytopathic changes including hyperkeratosis and ballooning degeneration of the keratinocytes. ORFV persisted for 10 days and was located in keratinocytes of the outer epidermal layers. ORFV-specific early, intermediate and late genes were transcribed, but limited viral spread and restricted cell infection were noticed. ORFV infection resulted in downregulation of K1, K10, and loricrin at the transcriptional level without affecting proliferation as shown by PCNA or Ki-67 expression. In conclusion, OTC provides a suitable model to study the interaction of virus with human keratinocytes in a similar structural setting as human skin and reveals that ORFV infection downregulates several differentiation markers in the epidermis of the human skin, a hitherto unknown feature of dermal ORFV infection in man.

Orf virus infection in Alaskan mountain goats, Dall's sheep, muskoxen, caribou and Sitka black-tailed deer

Background

The zoonotic Orf virus (ORFV; genus Parapoxvirus, Poxviridae family) occurs worldwide and is transmitted between sheep and goats, wildlife and man. Archived tissue samples from 16 Alaskan wildlife cases, representing mountain goat (Oreamnos americanus, n = 8), Dall’s sheep (Ovis dalli dalli, n = 3), muskox (Ovibos moschatus, n = 3), Sitka black-tailed deer (Odocoileus hemionus sitkensis, n = 1) and caribou (Rangifer tarandus granti, n = 1), were analyzed.

Results

Clinical signs and pathology were most severe in mountain goats, affecting most mucocutaneous regions, including palpebrae, nares, lips, anus, prepuce or vulva, as well as coronary bands. The proliferative masses were solid and nodular, covered by dark friable crusts. For Dall’s sheep lambs and juveniles, the gross lesions were similar to those of mountain goats, but not as extensive. The muskoxen displayed ulcerative lesions on the legs. The caribou had two ulcerative lesions on the upper lip, as well as lesions on the distal part of the legs, around the main and dew claws. A large hairless spherical mass, with the characteristics of a fibroma, was sampled from a Sitka black-tailed deer, which did not show proliferative lesions typical of an ORFV infection. Polymerase chain reaction analyses for B2L, GIF, vIL-10 and ATI demonstrated ORFV specific DNA in all cases. Sequences from Dall’s sheep formed a separate cluster, comparable to ORFV from domestic sheep. Sequences from the other species were different from the Dall’s sheep sequences, but almost identical to each other.

Conclusions

This is the first major investigation of parapoxvirus infections in large Alaskan game species, and the first report of parapoxvirus infection in caribou and Sitka black-tailed deer. This study shows that most of the wild ruminant species in Alaska and from most parts of Alaska, can carry and be affected by ORFV. These findings call for attention to transmission of ORFV from wildlife to livestock and to hunters, subsistence harvesters, and wildlife biologists.

Electronic supplementary material

The online version of this article (10.1186/s13028-018-0366-8) contains supplementary material, which is available to authorized users.

Role of autophagy in cellular response to infection with Orf virus Jilin isolate

Autophagy is a conserved catabolic process of the cell, which has been described to be involved in the development of various viral diseases. However, the role of autophagy in Orf virus (ORFV) replication remains unknown. In this study, we provide the first evidence that ORFV infection triggered autophagy in primary ovine fetal turbinate cells (OFTu) based on the appearance of abundant double- and single-membrane vesicles, the accumulation of LC3 fluorescent puncta, the enhancement of LC3-I/-II conversion, and autophagic flux. Moreover, modulation of ORFV-induced autophagy by rapamycin (RAPA), Earle's balanced salts solution (EBSS), chloroquine (CQ) or 3-methyladenime (3-MA) does not affect virus production. In conclusion, these results suggest that autophagy can be induced in host cells by ORFV infection, but which maybe not essential for ORFV replication.

Poxviral ankyrin proteins

Multiple repeats of the ankyrin motif (ANK) are ubiquitous throughout the kingdoms of life but are absent from most viruses. The main exception to this is the poxvirus family, and specifically the chordopoxviruses, with ANK repeat proteins present in all but three species from separate genera. The poxviral ANK repeat proteins belong to distinct orthologue groups spread over different species, and align well with the phylogeny of their genera. This distribution throughout the chordopoxviruses indicates these proteins were present in an ancestral vertebrate poxvirus, and have since undergone numerous duplication events. Most poxviral ANK repeat proteins contain an unusual topology of multiple ANK motifs starting at the N-terminus with a C-terminal poxviral homologue of the cellular F-box enabling interaction with the cellular SCF ubiquitin ligase complex. The subtle variations between ANK repeat proteins of individual poxviruses suggest an array of different substrates may be bound by these protein-protein interaction domains and, via the F-box, potentially directed to cellular ubiquitination pathways and possible degradation. Known interaction partners of several of these proteins indicate that the NF-κB coordinated anti-viral response is a key target, whilst some poxviral ANK repeat domains also have an F-box independent affect on viral host-range.

Infection with recombinant orf viruses demonstrates that the viral interleukin-10 is a virulence factor

Orf virus is the prototype parapoxvirus that causes the contagious skin disease orf. It encodes an orthologue of the cytokine interleukin (IL)-10. Recombinant orf viruses were constructed in which the viral interleukin-10 (vorfIL-10) was disabled (vorfIL-10ko) and reinserted (vorfrevIL-10) at the same locus and compared to wild-type virus for their ability to induce skin lesions in sheep. After either primary infection or reinfection, smaller less severe lesions were recorded in the vorfIL-10ko-infected animals compared with either of the vorfIL-10-intact virus-infected animals. Thus, the vorfIL-10ko virus was attenuated compared with the vorfIL-10 intact viruses, demonstrating that orf virus IL-10 is a virulence factor. The virus IL-10 is one of several virulence or immuno-modulatory factors expressed by orf virus. Removal of any one of these genes would be expected to have only a partial effect on virulence, which is what was observed in this study with vorfIL-10.

Genus Parapoxvirus

Highly contagious pustular skin infections of sheep, goats and cattle that were unwittingly transmitted to humans from close contact with infected animals, have been the scourge of shepherds, herdsmen and dairy farmers for centuries. In more recent times we recognise that these proliferative pustular lesions are likely to be caused by a group of zoonotic viruses that are classified as parapoxviruses. In addition to infecting the above ungulates, parapoxviruses have more recently been isolated from seals, camels, red deer and reindeer and most have been shown to infect man. The parapoxviruses have one of the smallest genomes of the poxvirus family (140 kb) yet share over 70% of their genes with the most virulent members. Like other poxviruses, the central core of the genomes encode factors for virus transcription and replication, and structural proteins, whereas the terminal regions encode accessory factors that give the parapoxvirus group many of its unique features. Several genes of parapoxviruses are unique to this genus and encode factors that target inflammation, the innate immune responses and the development of acquired immunity. These factors include a homologue of mammalian interleukin (IL)-10, a chemokine binding protein and a granulocyte-macrophage colony stimulating factor /IL-2 binding protein. The ability of this group to reinfect their hosts, even though a cell-mediated memory response is induced during primary infection, may be related to their epitheliotropic niche and the immunomodulators they produce. In this highly localised environment, the secreted immunomodulators only interfere with the local immune response and thus do not compromise the host’s immune system. The discovery of a vascular endothelial growth factor-like gene may explain the highly vascular nature of parapoxvirus lesions. There are many genes of parapoxviruses which do not encode polypeptides with significant matches with protein sequences in public databases, separating this genus from most other mammalian poxviruses. These genes appear to be involved in inhibiting apoptosis, manipulating cell cycle progression and degradation of cellular proteins that may be involved in the stress response, thus allowing the virus to subvert intracellular antiviral mechanisms and enhance the availability of cellular molecules required for replication. Parapoxviruses in common with Molluscum contagiosum virus lack a number of genes that are highly conserved in other poxviruses, including factors for nucleotide metabolism, serine protease inhibitors and kelch-like proteins. It is apparent that parapoxviruses have evolved a unique repertoire of genes that have allowed adaptation to the highly specialised environment of the epidermis.

Orf virus infection and host immunity

PURPOSE OF REVIEW

A summary of recent advances in our knowledge of the biology of orf virus is presented to illustrate the interaction of a zoonotic pathogen with host skin. This is providing novel and interesting data on the viral mechanism of skin infection and the host response.

RECENT FINDINGS

The full genome sequences of two parapoxviruses (orf virus and bovine papular stomatitis virus) have recently been published, defining the parapoxvirus genus at the molecular genetic level. This, along with more detailed characterization of viral immuno-modulatory proteins, is providing an insight into the acquisition of host genes and the mechanism of pathogenesis. A new chemokine-binding protein has been discovered with unique features. Structure-function analysis of the viral granulocyte/macrophage colony-stimulating factor inhibitory factor has revealed a similarity to type 1 cytokine receptors. The viral vascular endothelial growth factor-E stimulates angiogenesis in the skin without the side effects seen with cellular vascular endothelial growth factor-A, and may have therapeutic potential. Finally, orf virus is proving useful both as an immuno-modulator and as a vector for the expression of foreign antigens in non-permissive species.

SUMMARY

Orf virus infection provokes a vigorous skin immune response. However, the virus has acquired a range of immuno-modulatory/pathogenesis-related genes that function to limit (at least transiently) the effectiveness of host immunity. With the advent of the orf virus genome sequence, the study of this dynamic process will provide important insights into virus pathogenesis and the host skin immune response to infection.

Characterisation of parapoxviruses isolated from Norwegian semi-domesticated reindeer (Rangifer tarandus tarandus)

BACKGROUND

Two outbreaks of the disease contagious ecthyma were reported in 1999 and 2000 in Norwegian semi-domesticated reindeer (Rangifer tarandus tarandus). Contagious ecthyma is an epidermal disease of sheep and goats worldwide, which is caused by the zoonotic parapoxvirus orf virus. Characterisation of clinical samples from the two outbreaks in semi-domesticated reindeer in Norway by electron microscopy and PCR (B2L) revealed typical parapoxvirus particles and partial gene sequences corresponding to parapoxvirus, respectively. If contagious ecthyma in reindeer is caused by orf virus, the virus may be transferred from sheep and goats, via people, equipment and common use of pastures and corrals, to reindeer. Another possibility is that contagious ecthyma in reindeer is caused by a hitherto unclassified member of the parapoxvirus genus that circulates among reindeer herds and remains endemic in Norway.

RESULTS

Genomic comparisons of one standard orf strain (orf NZ2) and the reindeer isolates, employing restriction fragment length polymorphism (RFLP) and random amplified polymorphic DNA (RAPD) analysis, demonstrated high similarity between the reindeer viruses and known orf virus strains. Partial DNA sequences of two different viral genes were determined for the different isolates and compared with corresponding parapoxvirus genebank sequences. The comparison/alignment and construction of phylogenetic trees also point to an affiliation of the reindeer viruses to the species orf virus.

CONCLUSION

The results of this work imply that the parapoxvirus causing contagious ecthyma in Norwegian semi-domesticated reindeer belongs to the species orf virus and that the orf virus crosses the host species barrier from sheep and goat to semi-domesticated reindeer.