Review Article

Weapon Store of Contagious Ecthyma Virus: Accounting for Immune Evasion and Re-Infection Strategies in Target Hosts

Monu Karki, Amit Kumar and Gnanavel Venkatesan*

Indian Council of Agricultural Research (ICAR), Indian Veterinary Research Institute, India.

Received | March 18, 2022; Accepted | August 16, 2022; Published | December 26, 2022

*Correspondence | Gnanavel Venkatesan, Indian Council of Agricultural Research (ICAR), Indian Veterinary Research Institute, India; Email: [email protected]

Citation | Karki, M., Kumar, M. and Venkatesan, G., 2022. Weapon store of contagious ecthyma virus: Accounting for immune evasion and re-infection strategies in target hosts. Hosts and Viruses, 9: 19-31.

DOI | https://dx.doi.org/10.17582/journal.hv/2022/9.19.31

Keywords: Parapoxviruses, Orf virus, Virulence genes, Immune-evasion, Re-infection

Copyright: 2022 by the authors. Licensee ResearchersLinks Ltd, England, UK.

This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

Introduction

Viruses have gained a lot of attraction in the new era because of their ability to mutate fast and emerge into a whole new virus with varying host range and pathogenicity. There has been a long battle between viruses and humans since ages viz. 1918 Spanish flu to 2019 SARS-Cov-2 pandemic. Drastic environmental changes, ecologic and social habits of humans, and economic conditions have been an important factor in the transmission and emergence of various infectious diseases. The emerging and threatening viral diseases to public health put forth the need of “One Health approach” to study every potential virus in detail.

This review is focused on one of the most studied poxviruses after Vaccinia virus. Orf virus (ORFV) is known for its unique properties like immune evasion and re-infection in the host and has gained the interest of researchers in the present day. Orf is an important disease of small ruminants and also causes mild localized infections in humans [1]. It also affects camels, llamas, and some other wild animal species. Recent reports of ORFV infection in mountain goats, Sitka-black tailed deer, Dall’s sheep, muskox, and caribou indicates its host range switch ability [2]. Some reports of malignant lesion which often leads to death of animals are also reported [3]. The virus belongs to the family Poxviridae and carries many unique features viz. a number of virulence factors, immune evasion property, and inducing a short-lived immune response and thus re-infecting its host. The disease has been ignored by the small-scale farmers rearing small ruminants due to its self-limiting property and because of this notion, it has caused severe damage to the economy of many countries that have not even been recorded and resulted into spread to wild animals [3]. Although, an increasing number of recent reports on orf outbreak and its consequences, lack of proper attention and vaccines indicates that the virus is emerging to a more fatal form [3]. Different strains and recombination among the variants of virus are reported in one of the studies from Argentina, indicating the need for specific virus determination and specific vaccine [4].

Pathogenomics and virulence factor database for viruses

Pathogenomics is a field well known for bacterial virulence factor study [5] [6]. The study uses high-throughput genome sequencing and extensive bioinformatics for identifying genes encoding resistance or virulence factors [7]. Although a varied pool of virulence genes for different viruses has been already studied, the lacuna is a compilation of the data and a database. This database can help to ease the comparative studies while referring to immune evasion strategies of viruses and help in future challenges.

Virulence factors or genes of ORFV

Parapoxviruses are known to encode several virulence factors from the ends of the genome. Taken from the ancestral Poxviral genome or its host genome, these virulence genes have co-evolved with the virus to adapt it to host cell environments. A schematic of the location of different virulent genes or factors in the ORFV genome is presented in this review (Figure 1). These genes are not essential for viral replication in cell culture, but support the survival of virus in-vivo by helping the virus to replicate and survive in the specific immune environment [8]. Some of the unique PPV’s virulence genes are responsible for determining host range, pathogenesis, and virulence [9]. Some of the virulence genes are “captured” from the host during evolution like dUTPase, vIL-10, VEGF, Poxviral anaphase-promoting complex analog, and anti-apoptotic factors as indicated by their similarity to their cellular counterparts and absence from other Poxviral genomes [9]. This adaptation is probably because of the intricate relationship between host and virus. While CBP and GIF genes are believed to be the descendants of ancestral poxviral genes, NF-kB inhibitors genes found in PPVs are different from that of other poxviruses, without any similarity or homology. The review focuses on the on virulence genes of ORFV, as they hold potential for various uses like in the development of antiviral agent, immunomodulators, bio-therapeutics, and viral vectors [10]. List of potential virulent genes or factors of ORFV genome and their characteristics is depicted in Table 1.

 

VEGF (Vascular endothelial growth factor)

ORFV is the first among the viruses to report the presence of VEGF homologue VEGF-E. All the PPVs are known to encode the ORF132 (VEGF) gene from the 3’ terminal of the genome [9]. The VEGF glycoprotein binds the tyrosine kinase receptors, designated as VEGFRs present in the host cell and functions to enhance the oxygen and nutrient supply in infected cells to support virus survival and replication [11]. The gene is reported to be grouped as two different categories viz. VEGF-NZ7 and VEGF-NZ2 are based on differentiating inter-isolate variation [12]. Following this study, molecular epidemiology was done recently revealing the circulation of the VEGF-NZ7 gene containing isolates in India, and some from

 

Table 1: Compiling the key functions, ORF length in genome, their homologues if present in VACV and gene length of virulence genes

Virulence genes	ORF & VACV homologue	Key functions	Gene length
dUTPase	ORF007 (F2L)	Enhancing infection in non-dividing cells	506 bp
NF-kB acetylation inhibitor	ORF002	Inhibitor of NF-kB activation	344bp
NF-kB inhibitor	ORF024; ORF121	Inhibitor of NF-kB activation	875bp; 905bp
VEGF	ORF132	enhance the oxygen and nutrient supply in infected cells	446bp
GIF	ORF117 (A41L)	Manipulate chemokine response	794bp
Apoptosis inhibitor	ORF125	inhibits the mitochondrial downstream pathway of apoptosis	518bp
VIR	ORF020 (E3L)	Suppress antiviral activity by inactivating dsRNA induced interferons	548bp
vIL-10	ORF127	Suppress other defensive cytokines	551bp
CBP	ORF112 (C23L)	Bind and inactivate the cytokines and chemokines in infected cell	863bp
PACR/ Ring H2 protein	ORF014	Maintain infected cells in G0/G1 phase providing cells in sufficient supply	278bp

 

 

China and the rest known isolates possess VEGF-NZ2 type [13]. Mutational analyses suggested that the expression of VEGF in wild-type isolates leads to the formation of rete ridges with extensive epidermal proliferation and scab formation, which was not found in the recombinants [14]. Hence, peculiar finger-like projections of the lesions and involvement of VEGF in severe scab formation (Figure 2) can be correlated with the expression of VEGF [15]. The two types of VEGF genes can be a responsible factor for two types of lesions reported viz. severe and mild, which needs to be experimentally proved using both types of isolates. Even having the marked variation in the sequence, both the types possess conserved homodimeric structure and cysteine knot motif responsible for its activity [9, 15-16]. VEGF is specifically encoded by PPVs, whereas in other poxviruses, it is epidermal growth factor (EGF) only. For the same reason, the highly vascularized lesions of orf can be differentiated from the proliferative lesions of other poxviruses [9]. VEGF-E gene of the Vero cell-adapted attenuated ORFV D1701-V strain is found to be the most suitable target for insertion and expression of foreign genes and using it as an effective viral vector [17].

VIR (viral interferon resistance)

VIR is encoded by the ORF020 gene situated at the left end of the genome and utilizes the strategy providing the resistance to virus against interferon (Figure 1). VIR protein binds the interferon-induced dsRNA-dependent kinases, suppressing JAK-STAT signaling and subsequently their antiviral activity [9, 18]. VACV E3L gene is the only homolog shared by other poxviruses. ORF020 gene product can complement its homolog gene of VACV E3L in-vitro, as it shares 31% amino-acid identity [19]. The gene was found to show species-specific clusters in phylogenetic analysis, which is again an important finding to molecular epidemiology of the disease. The gene is found to be highly conserved among the genus, as well as among the different members of Poxviridae suggesting it as a good candidate for broad-spectrum antiviral [20].

PACR (poxvirus anaphase-promoting complex regulator)

ORFV along with its other PPV genus members encodes PACR to modulate the cell cycle in highly specialized immune epidermal cells, unlike most poxviruses that encode nucleotide metabolism enzymes like thymidine kinase and ribonucleotide reductase [9]. ORF014 gene encodes this protein which is similar to the APC11 subunit (RING H2 protein) of APC (Anaphase promoting complex) but lacks its functional ubiquitin ligase activity [21]. Therefore, the competitive binding of PACR to the C-terminal of APC2 subunit (a scaffold protein) in place of APC11 [22, 23] disturbs the functioning of APC and allows the cells to enter S phase [24]. The unbound APC11 subunit undergoes ubiquitination and proteasomal degradation. The unavailability of APC regulates the transition of the G1/S phase i.e., synthetic phase. ORFV-PACR like gene products is also found to be encoded by other poxviruses like MOCV and crocodile poxvirus. PACR gene which is common to all GC rich Chordopoxviruses and their specific targeting of epidermal cells suggest a link between the divergences of poxviruses [9]. Our lab studied that this gene possesses a specific difference in ORF lengths of sheep and goat isolates, reflected in the phylogenetic relationship. For the very first time, we found that the sheep and goat origin isolates can be differentially diagnosed through multiplex PCR (Unpublished data).

Apoptosis inhibitor

ORFV-125 gene encodes an anti-apoptotic product, a defensive phenomenon of the virus to prevent dying of host cells contain the spread of infection [25]. Sequence analysis of the ORF125 gene shows similarity in its C-terminal motif with Bcl-2-family members, but no homology to the VACV anti-apoptotic F1L gene and other poxviruses [26]. ORF125 protein binds and inactivates the BH3-range proteins, the pro-apoptotic members [27]. ORF125 shows 60-70% identity at the nucleotide level among ORFV isolates and PPVs but doesn’t show homology to any other viruses [9]. In contrast to the ORF125 gene, ORFV also encodes an apoptosis-inducing protein (ORF119) functioning by down-regulating the anti-apoptotic proteins Bcl-2 and cIAP-2 [28]. Transcriptome analysis of ORFV infected cells suggested that there is coordinated up and down-regulation of apoptosis-related genes and hence, links the viral interference in apoptosis [29].

dUTPase (dUTP pyrophosphatase)

An essential enzyme for nucleotide metabolism is encoded by ORF007 as an early protein, dUTPase [30]. Unlike other virulence genes, ORF007 is not essential for the in-vitro growth of ORFV, but in vivo, it enhances the replication of the virus in non-dividing cells [31]. The basic function of dUTPase is to hydrolyze the dUTP to dUMP and pyrophosphate (PPi). This limits the intracellular pool of dUTP and simultaneously provides the precursor (dUMP) for the synthesis of thymine maintaining the ratio of dUTP/dTTP. The increased concentration of dUTP in cells leads to the incorporation of uracil into DNA and other mutational changes [32]. Functional activity of dUTPase is found to be mainly regulated by five conserved amino acids “dUTPase motifs” acting as the active site of the enzyme [33-35]. The enzyme functions in a trimeric state and have the three active sites in which the tyrosine residue was found to be the active catalytic component as the functional loss of enzyme was demonstrated by its modifications (nitration and acetylation) [36]. This motif is reported to be found in all the dUTPase of viruses till now described viz. different retroviruses [37-41]. Therefore, its active site can be targeted for attenuation of the gene. Also, it has been described as a potential target for chemotherapeutic drugs [42]. The activity of dUTPase is found to be over the pH range of 6-9 and a temperature of 25-37°C [43]. This enzyme can be inhibited with an increased concentration of EDTA. Divalent cations like Mg+, MN+ act as co-factor to enhance its activity. ORFV dUTPase is more similar to mammalian dUTPase enzyme than other poxviruses, which suggests that it is acquired by the horizontal transfer from the host cell genome [44].

NF-ќB inhibitors

NF-kB (nuclear factor kappa-light-chain-enhancer of activated B cells) is a protein complex responsible for the regulation of immune response in infection. It is present in the cytosol of all cell types in an inactive state, bounded with IkB protein (inhibitor of kB). In response to any stimuli like infection, stress, etc., IKK (IkB kinase) is activated which destroys IkB [45]. Activated NF-kB is translocated to the nucleus, where it binds the DNA and helps it to transcribe the sequence, modulate its function accordingly to combat the change in the cell, and establish innate immune response. Hence, NF-kB inhibitors disrupt this process of immunity development. PPVs encoded NF-kB inhibitors are different from those encoded by other poxviruses like leporipoxvirus, molluscipoxvirus, yatapoxvirus, and orthopoxvirus suggesting the evolutionary deviations [46].

ORFV encodes three NF-kB inhibitory factors viz. ORF002, ORF024, and ORF121 [47-49]. The three factors have different functions but, eventually to inactivate the NF-kB signaling. Within the genus also, marked differences in homology have been reported [9]. ORF002 is an early-late protein of 117 amino acids, encoded from the left terminal region of the genome of PPV [50]. Among the three NF-κB inhibitors, the ORF002 is the first nuclear inhibitor having no homologs in other genera of the Chordopoxvirinae subfamily except equine molluscum contagiosum virus [51, 52]. Deletion mutants of ORF002 recommended the non-essential role of the gene in replication and virulence [48]. ORF002 and E1A protein of Adenovirus shares some conserved domains, therefore based on the comparative analysis, it was suggested that N-terminal amino acids of the ORF002 protein are responsible for blocking of phosphorylation of serine residue at 256 positions and thereby, inhibition of acetylation of NF-kB-p65 in the nucleus [53]. Notably, it was found that only the deletion of ORF121 has a significant change in virulence and pathogenesis [9]. ORF121 gene is conserved among its ORFV sheep and goat isolates and encoded early in the infection [47]. ORF121 binds NF-kB-p65 and inhibits its phosphorylation and nuclear translocation. Likewise, ORF024 inhibits the phosphorylation of IkB kinases and thereby inhibiting the activation of the IKK complex [49]. Despite tending to compact the genome, why the poxviruses encode several NF-kB inhibitors is a big question to the researchers [54].

Virokine, viral interleukin-10 (vIL-10)

vIL-10 was first reported in ORFV found to shares the remarkable functional similarity to ovine IL-10 at its C-terminal [9]. Similarly, virokine IL-10 has a suppressive effect on other cytokines that have inflammatory, antiviral, and other defensive roles [55]. ORF127 encodes the vIL-10 gene early in the infection from the right end of the genome, which plays a vital role in the establishment of virus infection. Both the IL-10R1 and IL-10R2 receptors are necessary for the activity of vIL-10 [56]. Recombinant ORFV having a deletion of ORF127 demonstrated the reduction in virulence and attenuation of the virus [57]. Sequence analysis of the vIL-10 gene from various species has suggested the variation in its amino-terminal, while the carboxy terminus of the gene was found to be conserved and responsible for virulence activity [58]. Low GC content of viral interleukin-10 gene, in contrast to the high GC content of ORFV genome and marked homology at its C-terminal to ovine IL-10 than to other viral IL-10 supports the findings that the gene is acquired from the host [59]. The DNA sequence of ORFV-IL-10 was found to have many synonymous substitutions from its host counterpart, which indicates the horizontal transfer of a gene from the host and evolutionary changes adapted by the ORFV [9]. Alternatively, other members of the genus PPV possess the amino-acid identity to the gene from their host counterparts, not to ORFV, indicating the independent horizontal transfer of the gene from specific hosts [60]. Other poxviruses like Yatapoxvirus and Capripoxvirus possess IL-24 encoding gene, an IL-10 family member [61, 62]. A report from Rajasthan, India stated that vIL-10 from the skin scab of PPV infected camel (Camel contagious ecthyma) resembles more closely to Pseudocowpoxvirus of cattle than ORFV of sheep based on sequence analysis, revealing the transfer of the virus from cattle to camel [58].

Viroceptors of ORFV: GM-CSF and IL-2 inhibitory factor (GIF) and Chemokine binding protein (CBP)

Poxviruses encode several proteins which challenges the chemokine mediated inflammatory response of host cell [63]. ORFV encodes two genes responsible for binding the important chemokines in the infected cells and disrupting their biological function to protect the cells. GIF, is encoded by ORF117 gene of PPVs only and binds two chemokines viz. GM-CSF and IL-2. The two cytokines are completely different in their binding domains [64]. CBP, an early 2.5A° soluble protein is encoded by ORF112 and is also present in other PPVs and members of the family [65, 66]. Chemokine-binding proteins inhibit host chemokine trafficking, especially of dendritic cells and monocytes to the infected cells and don’t possess any similarity to any of the host proteins [67-69]. This is one of the reasons why adaptive immunity doesn’t take a full hand in the case of ORFV. The two genes share high homology indicating duplication of the gene during evolution [9]. GIF activity corresponds to the WSXWS-like motif, which is responsible for dimer and tetramer formations, i.e. its functional state [70]. Conserved cysteine residues form disulfide bond important for maintaining tertiary structure of the protein, essential for binding to cytokines [71]. The functional activity of BPSV-ORF117 was found to be deviated from others, indicating more relatedness of ORFV and PCPV than BPSV [72]. The receptors of human and murine GM-CSF and IL-2 have been cloned and characterized, but these don’t share any similarity to the ORFV-GIF [73]. The ORFV-GIF binds only the ovine GM-CSF and IL-10, which emphasizes its adaptation to its particular hosts.

An analysis of the sequence of vCBP shows more similarity to GIF (GM-CSF and IL-2 inhibitory factor) than type-2 CC-chemokine binding protein family, indicating the evolution from the same ancestral gene [74]. The gene is conserved within the genus with a varied percentage of identity but shares low identity with other poxviruses CBP [9]. Recently, infection studies conducted based on the deletion mutants of CBP, wild type (wt) ORFV and revertant virus were carried out in sheep to prove its role in virulence, pathogenesis and host response [75]. Hence, the recombinants may prove as good subunit vaccine candidate as significant change in antibody response was observed for knock-out ORFV than wt and revertant virus.GIF and CBP are important virulence factors of ORFV, distantly related to the 35kDa protein family. GIF is a highly conserved gene of PPVs and possesses the ‘WDPWV’ and SUSHI domain. The SUSHI/CCP/SCR domain is basically a conserved protein domain with a structure consisting of a protein loop within another loop. CBP possesses high variations among ORFV as well as other poxviruses. For the first time, the presence of SUSHI domain in GIF gene of ORFV isolates from India has been reported [76].

Orf virus induced immunity in host

ORF011 and ORF059 encoded proteins are immunodominant and responsible for inducing immune response [77]. However, few and weak neutralizing antibodies are found in serum of infected animals. Neutrophils, natural killer cells, dendritic cells are observed to in infected cells after infection and a rush of cytokine has also been observed [78]. Similarly, Th1 response was found to comparatively confer strong cell-mediated immunity.Also, MHC-II+ dendritic cells population was observed in PPOV infected sheep [79]. However, the clear picture of immunity development is not clear till date, and need a specified stage-wise in-vivo experimental study to clear innate as well adaptive immunity phases of the disease. Biggest challenge is escaping the immunity developed and re-infecting the same host. Most probable reason is these virulence factors that help the virus to manipulate the immune environment of host cell. The re-infection is the major problem faced by livestock health sector to control this disease.

Applications of ORFV

Firstly, the Poxviruses have always played an important role as vaccine vectors viz. modified VACV Ankara (MVA), fowlpoxvirus, canarypoxvirus, and now the ORFV [80]. A Vero-cell culture adapted attenuated strain/apathogenic ORFV-D1701-V strain has been proved itself as an efficient immunomodulatory virus vector to develop recombinants via replacing VEGF-E gene with an insert often referred as an inactivated Parapoxvirusovis (iPPVO). VEGF-E is the most important gene in orf virulence and thereby this replacement subsequently reduces the disease pathogenicity.This vector has been used to develop vaccines against many diseases in the last two decades. Pseudorabies virus (PRV) glycoproteins gC and gD based ORFV-D1701 vector vaccine have shown both humoral and cellular immunity against natural infection in mice [81]. Another example of recombinant iPPVO as vector vaccine replacing VEGF-gene by rabies virus G glycoprotein successfully mounted protective immunity against lethal challenge infection in mice [82].

Also, iPPVO expressing PRV-gC and gD is used as booster dose for activation of strong immunity and found to be more efficient than other prime-boost regimens [83, 84]. Also, iPPVO plays a key role as antiviral immunotherapeutic against Herpes simplex virus, Hepatitis B virus, rabbit haemorrhagic disease and etc[85, 86]. This has been used to track the immune response by the host cell against iPPVO. A complex cytokine response from different immune cells including both Th1-related (IL-12, IL-18, IFN-ɣ) and Th2-regulatory cytokines (IL-4) was demonstrated in Equine, mice, and rats, in-vivo [87-90]. Also, the iPPVOinduces the secretion of IFN-α and–β by dendritic cells via TLR-independent pathways [91]. Human peripheral cells have also been showing induction of Th-1 cell and monocyte-related cytokines [92]. Even in non-permissive cells, canine polymorphonuclear cells (in-vitro), iPPVO induction demonstrated an enhanced phagocytic activity, MHC-II upregulation, and CD4+ T-cell proliferation, and oxidative burst in monocytes [93]. The immunostimulating effect of this inactivated ORFV expressing H5 has proved to protect against high pathogenic strains of avian influenza H5N1 and H1N1 in mice [94, 95]. Whereas, a study shows iPPVO co-culture with Equine Herpes virus-1 and 4 does not affect the viral proliferation and increased IL-10 mRNA and multi-cytokine expression [96].

Secondly, ORFV has joined the legacy of poxviruses as a potent oncolytic virus candidate for cancer biotherapyand has shown remarkably pronounced effects in murine cancer models [97]. They are widely accepted because of skin tropism, strong induction of innate immunity at the infection site, and no systemic invasion. IFN-ɣ and IL-10 induction by iPPVO directs the study towards its anti-fibrotic therapeutic approach and found to exercise it successfully in pre-established liver fibrosis in rat models [98]. Its widening applications have also touched the acaricidal therapy to treat canine generalized demodicosis via the combination of amitraz and iPPVO and provide faster recovery than amitraz alone [99]. This non-specific immunomodulator is also found to be effective in equine respiratory diseases when used along with Propionibacterium acnes [100].

By modulating the immune response of the host, some of the genes have been used as therapeutic agent for certain important inflammatory diseases. Synthetically produced VEGF using recombinant DNA technology can be used in conditions like hypoxia to restore the oxygen supply to tissues when blood circulation is inadequate and also to provide nutrient supply to regenerate the affected cell [101].The synergistic effect of ORFV-VEGF and IL-10 immunomodulatory proteins has been studied to treat wounds in a murine model recently, resulting in the expected outcome of enhanced wound closure, re-vascularisation, re-epitheliasation and less wound scarring [102]. Rabies virus G and M protein based VLP containing membrane anchored immunostimulatory molecule, GM-CSF, induces enhanced immunogenicity and 100% protection against wild type virus [103]. MOR103 drug is available to control high levels of GM-CSF found in joints with rheumatoid arthritis [104]. Likewise, pathogenesis behind diseases like psoriasis itching involved, due to over-expression of IL-2 can be controlled. The IL-2 used as therapeutic agent has been also known to determine the severity of the side effects [105], therefore in these cases also GIF can be used effectively.

Conclusions and Recommendations

Earlier, orf virus was known only as an entity causing mild self-limiting disease of sheep and goats. Later, its varied range of virulence factors, re-infection causing ability, and widening host range to wild animals gained the attraction of researchers to study the virus and its genome in more detail. Some of the important virulence factors are known to acquire from their respective hosts via horizontal gene transfer namely VEGF, IL-10, PACR etc for utilizing them against host defense mechanism. Ironically, the same genes can be used by certain manipulations for our benefits. VEGF is the most studied virulence factor of ORFV, followed by GIF, CBP and vIL-10 and they have been proved as potential candidates as biotherapeutics.Other virulence factors like dUTPase, VIR, apoptosis inhibitor, NF-kB inhibitors are still at the primary stage of study after being noticed in the genome of ORFV. The virus has evolved through many adaptations to ensure its presence in the environment and host. In the last decade, various uses of ORFV have been studied extensively as viral vector for other important diseases, bio-therapeutic for medical important diseases like cancer. We need to keep up our ability to fight against these small entities and maintain the balance of ecology.

Acknowledgment

The authors thank the Director, Indian Veterinary Research Institute for providing the necessary facilities to carry out this study. The financial support provided by DBT, India under the North-East Twinning program on DBT-NER on Pox project (BT/385/NE/TBP/2012) is also acknowledged.

Abbreviations

Viral interferon resistance gene (VIR), Vascular endothelial growth factor (VEGF), viral interleukin-10 (vIL-10), GM-CSF and Interleukin-2 inhibitory factor (GIF), Chemokine binding protein (CBP), Poxviral anaphase promoting complex regulator analog (PACR).

Novelty Statement

The MS entitled “Weapon Store of Contagious Ecthyma Virus: Accounting for Immune Evasion and Re-Infection Strategies in Target Hosts” focuses on the important virulence genes of the orf virus and their functions with recent advances and the way they can be manipulated for different benefits to the research community viz candidates for cancer biotherapy, immunomodulators, antivirals, viral vectors, and recombinant vaccines.

Author’s Contribution

MK and VG planned, collected the data and prepared the draft. AK and VG edited and revised the review for final submission.

Conflict of interest

The authors have declared no conflict of interest.

References

Amann, R., Rohde, J., Wulle, U., Conlee, D., Raue, R., et al., 2013. A new rabies vaccine based on a recombinant ORF virus (parapoxvirus) expressing the rabies virus glycoprotein. J. Virol., 87(3): 1618-1630. https://doi.org/10.1128/JVI.02470-12

Anziliero, D., Weiblen, R., Kreutz, L.C., Spilki, F., Flores, E.F., 2014. Inactivated parapoxvirusovis induces a transient increase in the expression of proinflammatory, Th1-related, and autoregulatory cytokines in mice. Braz. J. Med. Biol. Res., 47(2): 110-118. https://doi.org/10.1590/1414-431X20133358

Avci, O., Bulut, O., and Dik, I., 2015. Effects of inactive parapoxvirusovis on cytokine levels in rats. J. Vet. Med. Sci., 15: 0231.

Baer, R., Bankier, A.T., Biggin, M.D., Deininger, P.L., Farrell, P.J., et al., 1984. DNA sequence and expression of the B95-8 Epstein Barr virus genome. Nature, 310(5974): 207-211. https://doi.org/10.1038/310207a0

Baggiolini, M., 1998. Chemokines and leukocyte traffic. Nature, 392(6676): 565. https://doi.org/10.1038/33340

Bala, J.A., Balakrishnan, K.N., Abdullah, A.A., Mohamed, R., Haron, A.W., et al., 2018. The re-emerging of orf virus infection: A call for surveillance, vaccination and effective control measures. Microbial Pathog., 120: 55-63. https://doi.org/10.1016/j.micpath.2018.04.057

Baldo, A.M., and McClure, M.A., 1999. Evolution and horizontal transfer of dUTPase-encoding genes in viruses and their hosts. J. Virol., 73: 7710-7721. https://doi.org/10.1128/JVI.73.9.7710-7721.1999

Bazan, J.F., 1990. Structural design and molecular evolution of a cytokine receptor superfamily. Proc. Natl. Acad. Sci., 87(18): 6934-6938. https://doi.org/10.1073/pnas.87.18.6934

Behrens, F., Tak, P.P., Ostergaard, M., Stoilov, R., Wiland, P., et al., 20140. MOR103, a human monoclonal antibody to granulocyte–macrophage colony-stimulating factor, in the treatment of patients with moderate rheumatoid arthritis: Results of a phase Ib/IIarandomised, double-blind, placebo-controlled, dose-escalation trial. Ann. Rheum. Dis., 74(6): 1058-1064. https://doi.org/10.1136/annrheumdis-2013-204816

Broyles, S.S., 1993. Vaccinia virus encodes a functional dUTPase. Virology, 195: 863-865. https://doi.org/10.1006/viro.1993.1446

Büttner, M., Rziha, H.J., 2002. Parapoxviruses from the lesion to the viral genome. J. Vet. Med. Ser. B, 49(1): 7-16. https://doi.org/10.1046/j.1439-0450.2002.00539.x

Chen, L., Yang, J., Yu, J., Yao, Z., Sun, L., et al., 2005. VFDB: A reference database for bacterial virulence factors. Nucl. Acids Res., 33: D325-D328. https://doi.org/10.1093/nar/gki008

Chen, L., Xiong, Z., Sun, L., Yang, J., Jin, Q., 2012. Update: toward the genetic diversity and molecular evolution of bacterial virulence factors. Nucl. Acids Res., 40(D1): D641-D645. https://doi.org/10.1093/nar/gkr989

Cottone, R., Buttner, M., McInnes, C.J., Wood, A.R., Rziha, H.J., 2002. Orf virus encodes a functional dUTPase gene. J. Gen. Virol., 83: 1043-1048. https://doi.org/10.1099/0022-1317-83-5-1043

Counago, R.M., Fleming, S.B., Mercer, A.A., Krause, K.L., 2010. Crystallization and preliminary X-ray analysis of the chemokine-binding protein from orf virus (Poxviridae). Acta Crystallogr. Sect. F, 66: 819-823. https://doi.org/10.1107/S1744309110018166

Davison, A.J., and Scott, J.E., The complete DNA sequence of varicella-zoster virus. J. Gen. Virol., 67(9): 1759-1816. https://doi.org/10.1099/0022-1317-67-9-1759

Deane, D., McInnes, C.J., Percival, A., Wood, A., Thomson, J., et al., 2000. Orf virus encodes a novel secreted protein inhibitor of granulocyte-macrophage colony-stimulating factor and interleukin-2. J. Virol., 74: 1313–1320. https://doi.org/10.1128/JVI.74.3.1313-1320.2000

Deane, D., Ueda, N., Wise, L.M., Wood, A.R., Percival, A., et al. 2009. Conservation and variation of the parapoxvirus GM-CSF-inhibitory factor (GIF) proteins. J. Gen. Virol., 90(4): 970-977. https://doi.org/10.1099/vir.0.006692-0

Delhon, G., Tulman, E.R., Afonso, C.L., Lu, Z., Concha-Bermejillo, A., et al., 2004. Genomes of the parapoxviruses orf virus and bovine papular stomatitis virus. J. Virol., 78: 168-177. https://doi.org/10.1128/JVI.78.1.168-177.2004

Diel, D.G., Delhon, G., Luo, S., Flores, E.F., Rock, D.L., 2010. A novel inhibitor of the NF-{kappa} B signaling pathway encoded by the parapoxvirus virus. J. Virol., 84: 3962–3973. https://doi.org/10.1128/JVI.02291-09

Diel, D.G., Luo, S., Delhon, G., Peng, Y., Flores, E.F., et al. 2011. A nuclear inhibitor of NF-kappaB encoded by a poxvirus. J. Virol., 85: 264–275. https://doi.org/10.1128/JVI.01149-10

Diel, D.G., Luo, S., Delhon, G., Peng, Y., Flores, E.F., et al., 2011. Orf virus ORFV121 encodes a novel inhibitor of NF-kappaB that contributes to virus virulence. J. Virol., 85: 2037–2049. https://doi.org/10.1128/JVI.02236-10

Dory, D., Fischer, T., Béven, V., Cariolet, R., Rziha, H.J., et al. 2006. Prime-boost immunization using DNA vaccine and recombinant Orf virus protects pigs against Pseudorabies virus (Herpes suid 1). Vaccine, 24(37-39): 6256-6263. https://doi.org/10.1016/j.vaccine.2006.05.078

Ehmann, R., Brandes, K., Antwerpen, M., Walter, M., Schlippenbach, K., et al., 2020. Molecular and genomic characterization of a novel equine molluscum contagiosum-like virus. J. Gen. Virol., 102(3). https://doi.org/10.1099/jgv.0.001357

Everett, H., and McFadden, G., 2002. Poxviruses and apoptosis: A time to die. Curr. Opin. Microbiol., 5: 395–402. https://doi.org/10.1016/S1369-5274(02)00340-5

Felix, J., Kandiah, E., De Munck, S., Bloch, Y., Van Zundert, G.C., et al., 2016. Structural basis of GM-CSF and IL-2 sequestration by the viral decoy receptor GIF. Nature Commun., 7: 13228. https://doi.org/10.1038/ncomms13228

Fiebig, H.H., Siegling, A., Volk, H.D., Friebe, A., Knolle, P., et al., 2011. Inactivated orf virus (Parapoxvirusovis) induces antitumoral activity in transplantable tumor models. Anticancer Res., 31(12): 4185-4190.

Fischer, T., Planz, O., Stitz, L., and Rziha, H.J., 2003. Novel recombinant parapoxvirus vectors induce protective humoral and cellular immunity against lethal herpesvirus challenge infection in mice. J. Virol., 77(17): 9312-9323. https://doi.org/10.1128/JVI.77.17.9312-9323.2003

Fleming, S.B., Lyttle, D.J., Sullivan, J.T., Mercer, A.A., Robinson, A.J., 1995. Genomic analysis of a transposition-deletion variant of orf virus reveals a 3.3 kb region of non-essential DNA. J. Gen. Virol., 76: 2969-2978. https://doi.org/10.1099/0022-1317-76-12-2969

Fleming, S.B., McCaughan, C., Lateef, Z., Dunn, A., Wise, L.M., et al., 2017. Deletion of the chemokine binding protein gene from the Parapoxvirus Orf virus reduces virulence and pathogenesis in sheep. Front. Microbiol., 8: 46. https://doi.org/10.3389/fmicb.2017.00046

Fleming, S.B., Wise, L.M., Mercer, A.A., 2015. Molecular genetic analysis of orf virus: A poxvirus that has adapted to skin. Viruses, 7(3): 1505-1539. https://doi.org/10.3390/v7031505

Fleming, S.B., Anderson, I.E., Thomson, J., Deane, D.L., McInnes, C.J., et al., 2007. Infection with recombinant orf viruses demonstrates that the viral interleukin-10 is a virulence factor. J. Gen. Virol., 88(7): 1922-1927. https://doi.org/10.1099/vir.0.82833-0

Friebe, A., Friederichs, S., Scholz, K., Janssen, U., and Scholz, C., et al., 2011. Characterization of immunostimulatory components of orf virus (parapoxvirusovis). J. Gen. Virol., 92(7): 1571-1584. https://doi.org/10.1099/vir.0.028894-0

Friebe, A., Siegling, A., Friederichs, S., Volk, H.D., and Weber, O., 2004. Immunomodulatory effects of inactivated parapoxvirusovis (ORF virus) on human peripheral immune cells: induction of cytokine secretion in monocytes and Th1-like cells. J. Virol., 78(17): 9400-9411. https://doi.org/10.1128/JVI.78.17.9400-9411.2004

González-Motos, V., Kropp, K.A., Viejo-Borbolla, A., 2016. Chemokine binding proteins: An immunomodulatory strategy going viral. Cytokine Growth Factor Rev., 30: 71-80. https://doi.org/10.1016/j.cytogfr.2016.02.007

Haig, D.M., McInnes, C., Deane, D., Reid, H., and Mercer, A.A., The immune and inflammatory response to orf virus. Comp. Microbiol. Immunol., 20(3): 197-204. https://doi.org/10.1016/S0147-9571(96)00045-8

Haig, D.M., McInnes, C.J., Thomson, J., Wood, A., Bunyan, K., et al., 1998. The orf virus OV20.0L gene product is involved in interferon resistance and inhibits an interferon-inducible, double-stranded RNA-dependent kinase. Immunology, 93: 335–340. https://doi.org/10.1046/j.1365-2567.1998.00438.x

Haller, S.L., Peng, C., McFadden, G., and Rothenburg, S., 2014. Poxviruses and the evolution of host range and virulence. Infect. Genet. Evol., 21: 15-40. https://doi.org/10.1016/j.meegid.2013.10.014

Horohov, D.W., Breathnach, C.C., Sturgill, T.L., Rashid, C., Stiltner, J.L., et al., 2008. In vitro and in vivo modulation of the equine immune response by parapoxvirusovis. Equine Vet. J., 40(5): 468-472. https://doi.org/10.2746/042516408X322111

Hue, E., Richard, E., Fortier, C., Fortier, G., Paillot, R., et al., 2017. Equine PBMC Cytokines Profile after In Vitro α-and γ-EHV Infection: Efficacy of a Parapoxvirus Ovis Based-Immunomodulator Treatment. Vaccines, 5(3): 28. https://doi.org/10.3390/vaccines5030028

Hughes, A.L., Irausquin, S., Friedman, R., 2010. The evolutionary biology of poxviruses. Infect. Genet. Evol., 10(1): 50-59. https://doi.org/10.1016/j.meegid.2009.10.001

Jia, H., Zhan, L., Wang, X., He, X., Chen, G., et al., 2017. Transcriptome analysis of sheep oral mucosa response to Orf virus infection. PLoS One, 12(10): e0186681. https://doi.org/10.1371/journal.pone.0186681

Kang, H., Qi, Y., Wang, H., Zheng, X., Gao, Y., et al., 2015. Chimeric rabies virus-like particles containing membrane-anchored GM-CSF enhances the immune response against rabies virus. Viruses, 7(3): 1134-1152. https://doi.org/10.3390/v7031134

Karin, M., Ben-Neriah, Y., 2000. Phosphorylation meets ubiquitination: The control of NF-κB activity. Ann. Rev. Immunol., 18(1): 621-663. https://doi.org/10.1146/annurev.immunol.18.1.621

Karki, M., Kumar, A., Arya, S., Ramakrishnan, M.A., and Venkatesan, G., 2019. Poxviral E3L ortholog (Viral Interferon resistance gene) of orf viruses of sheep and goats indicates species-specific clustering with heterogeneity among parapoxviruses. Cytokine, 120: 15-21. https://doi.org/10.1016/j.cyto.2019.04.001

Karki, M., Kumar, A., Arya, S., and Venkatesan, G., 2020. Circulation of Orf viruses containing the NZ7-like vascular endothelial growth factor (VEGF-E) gene type in India. Virus Res., 197908. https://doi.org/10.1016/j.virusres.2020.197908

Karki, M., Venkatesan, G., Kumar, A., Kumar, S., and Bora, D.P., 2019. Contagious ecthyma of sheep and goats: A comprehensive review on epidemiology, immunity, diagnostics and control measures. Veterinarskiarhiv, 89(3): 393-423.

Karki, M., Venkatesan, G., Kumar, A., and Pandey, A.B., 2022. Genetic analysis of two viroceptor genes of orf virus. Archives of Virology (Accepted for publication).

Kornberg, A., Baker, T.A., 1992. DNA Replication. 2nd New York, pp. 931.

Kotenko, S.V., Krause, C.D., Izotova, L.S., Pollack, B.P., Wu, W., et al., 1997. Identification and functional characterization of a second chain of the interleukin-10 receptor complex. EMBO J., 16(19): 5894-5903. https://doi.org/10.1093/emboj/16.19.5894

Lalani, A.S., McFadden, G., 1997. Secreted poxvirus chemokine binding proteins. J. Leukoc. Biol., 62(5): 570-576. https://doi.org/10.1002/jlb.62.5.570

Lateef, Z., Baird, M.A., Wise, L.M., Mercer, A.A., Fleming, S.B., Orf virus-encoded chemokine-binding protein is a potent inhibitor of inflammatory monocyte recruitment in a mouse skin model. J. Gen. Virol., 90(6): 1477-1482. https://doi.org/10.1099/vir.0.009589-0

Lee, H.J., Essani, K., Smith, G.L., The genome sequence of Yaba-like disease virus, a yatapoxvirus. Virology, 281(2): 170-192. https://doi.org/10.1006/viro.2000.0761

Li, W., Chen, H., Deng, H., Kuang, Z., Long, M., et al., 2018. Orf virus encoded protein ORFV119 induces cell apoptosis through the extrinsic and intrinsic pathways. Front. Microbiol., 9: 1056. https://doi.org/10.3389/fmicb.2018.01056

Lin, F.Y., Tseng, Y.Y., Chan, K.W., Kuo, S.T., Yang, C.H., et al., 2015. Suppression of influenza virus infection by the orf virus isolated in Taiwan. J. Vet. Med. Sci., 14-0663.

McClure, M.A., Johnson, M.S., and Doolittle, R.F., 1987. Relocation of a protease-like gene segment between two retroviruses. Proc. Natl. Acad. Sci. USA, 84(9): 2693-2697. https://doi.org/10.1073/pnas.84.9.2693

McColl, B.K., Stacker, S.A., and Achen, M.G., 2004. Molecular regulation of the VEGF family -inducers of angiogenesis and lymphangiogenesis. APMIS, 112: 463- 480. https://doi.org/10.1111/j.1600-0463.2004.apm11207-0807.x

McGeoch, D.J., Dalrymple, M.A., Davison, A.J., Dolan, A., Frame, M.C., et al., 1988. The complete DNA sequence of the long unique region in the genome of herpes simplex virus type 1. J. Gen. Virol., 69(7): 1531-1574. https://doi.org/10.1099/0022-1317-69-7-1531

McGeoch, D.J., 1990. Protein sequence comparisons show that the ‘pseudoproteases’ encoded by poxviruses and certain retroviruses belong to the deoxyuridine triphosphatase family. Nucl. Acids Res., 18(14): 4105-4110. https://doi.org/10.1093/nar/18.14.4105

McInnes, C.J., Deane, D., Haig, D., Percival, A., Thomson, J., et al., 2005. Glycosylation, disulfide bond formation, and the presence of a WSXWS-like motif in the orf virus GIF protein are critical for maintaining the integrity of Binding to ovine granulocyte-macrophage colony-stimulating factor and interleukin-2. J. Virol., 79(17): 11205-11213. https://doi.org/10.1128/JVI.79.17.11205-11213.2005

McIntosh, E.M., Haynes, R.H., 1996. dUTP pyrophosphatase as a potential target for chemotherapeutic drug development. Acta Biochim. Pol., 44(2): 159-171. https://doi.org/10.18388/abp.1997_4410

Mercer, A.A., Fraser, K.M., Stockwell, P.A., Robinson, A.J., 1989. A homologue of retroviral pseudoproteases in the parapoxvirus, orf virus. Virology, 172(2): 665-668. https://doi.org/10.1016/0042-6822(89)90212-2

Mercer, A.A., Wise, L.M., Scagliarini, A., McInnes, C.J., Buttner, M., et al., 2002. Vascular endothelial growth factors encoded by orf virus show surprising sequence variation but have a conserved, functionally relevant structure. J. Gen. Virol., 83: 2845-2855. https://doi.org/10.1099/0022-1317-83-11-2845

Mo, M., Fleming, S.B., Mercer, A.A., 2009. Cell cycle deregulation by a poxvirus partial mimic of anaphase-promoting complex subunit 11. Proc. Nat. Acad. Sci. USA, 106: 19527–19532. https://doi.org/10.1073/pnas.0905893106

Mo, M., Fleming, S.B., Mercer, A.A., 2010. Orf virus cell cycle regulator, PACR, competes with subunit 11 of the anaphase promoting complex for incorporation into the complex. J. Gen. Virol., 91: 3010-3015. https://doi.org/10.1099/vir.0.026054-0

Mo, M., Shahar, S., Fleming, S.B., Mercer, A.A., 2012. How viruses affect the cell cycle through manipulation of the APC/C. Trends Microbiol., 20: 440–448. https://doi.org/10.1016/j.tim.2012.05.007

Mohamed, M.R., and McFadden, G., 2009. NF-kB inhibitors: Strategies from poxviruses. Cell Cycle, 8: 3125–3132. https://doi.org/10.4161/cc.8.19.9683

Moore, K.W., de Waal, Malefyt, R., Coffman, R.L., O’Garra, A., 2001. Interleukin-10 and the interleukin-10 receptor. Ann. Rev. Immunol., 19(1): 683-765. https://doi.org/10.1146/annurev.immunol.19.1.683

Nagarajan, G., Swami, S.K., Dahiya, S.S., Sivakumar, G., Narnaware, S.D., et al. 2013. Comparison of virokine from camel pseudocowpoxvirus (PCPV) with Interleukin 10 of the Dromedary camel (Camelus dromedarius). Cytokine, 61(2): 356-359. https://doi.org/10.1016/j.cyto.2012.12.008

Ning, Z., Zheng, Z., Hao, W., Duan, C., Li, W., et al., 2013. The N terminus of orf virus-encoded protein 002 inhibits acetylation of NF-κB p65 by preventing Ser 276 phosphorylation. PLoS One, 8(3): e58854. https://doi.org/10.1371/journal.pone.0058854

Nowatzky, J., Knorr, A., Hirth-Dietrich, C., Siegling, A., Volk, H.D., et al., 2013. Inactivated Orf virus (Parapoxvirusovis) elicits antifibrotic activity in models of liver fibrosis. Hepatol. Res., 43(5): 535-546. https://doi.org/10.1111/j.1872-034X.2012.01086.x

Paillot, R., 2013. A systematic review of the immune-modulators Parapoxvirusovis and Propionibacterium acnes for the prevention of respiratory disease and other infections in the horse. Vet. Immunol. Immunopathol., 153(1-2): 1-9. https://doi.org/10.1016/j.vetimm.2013.01.010

Palmer, B.F., Clegg, D.J., 2014. Oxygen sensing and metabolic homeostasis. Mol. Cell Endocrinol., 397(1): 51-58. https://doi.org/10.1016/j.mce.2014.08.001

Pekmezci, D., Pekmezci, G.Z., Guzel, M., Cenesiz, S., Gurler, A.T., et al., 2014. Efficacy of amitraz plus inactivated parapoxvirusovis in the treatment of canine generalized demodicosis. Vet. Rec., 174(22). https://doi.org/10.1136/vr.102226

Peralta, A., Robles, C.A., Micheluod, J.F., Rossanigo, C.E., Martinez, A., et al., 2018. Phylogenetic analysis of ORF viruses from five contagious ecthyma outbreaks in Argentinian goats. Front. Vet. Sci., 5: 134. https://doi.org/10.3389/fvets.2018.00134

Pines, J., 2011. Cubism and the cell cycle: The many faces of the APC/C. Nat. Rev. Mol. Cell Biol., 12: 427-438. https://doi.org/10.1038/nrm3132

Rezende, A.L.R.A., Bernardes, F.F., de Paula, N.A., Towersey, L., Hay, R., et al., 2018. Clinical manifestation, dermoscopy, and scanning electron microscopy in two cases of contagious Ecthyma (Orf nodule). Case reports in dermatological medicine. https://doi.org/10.1155/2018/2094086

Robinson, A.J., Barns, G., Fraser, K., Carpenter, E., Mercer, A.A., 1987. Conservation and variation in orf virus genomes. Virology, 157(1): 13-23. https://doi.org/10.1016/0042-6822(87)90308-4

Rohde, J., Amann, R., Rziha, H.J., 2013. New Orf virus (Parapoxvirus) recombinant expressing H5 hemagglutinin protects mice against H5N1 and H1N1 influenza A virus. PLoS One, 8(12): e83802. https://doi.org/10.1371/journal.pone.0083802

Rohde, J., Schirrmeier, H., Granzow, H., Rziha, H.J., 2011. A new recombinant Orf virus (ORFV, Parapoxvirus) protects rabbits against lethal infection with rabbit hemorrhagic disease virus (RHDV). Vaccine, 29(49): 9256-9264. https://doi.org/10.1016/j.vaccine.2011.09.121

Rziha, H.J., Bauer, B., Adam, K.H., Röttgen, M., Cottone, R., et al., 2003. Relatedness and heterogeneity at the near-terminal end of the genome of a parapoxvirusbovis 1 strain (B177) compared with parapoxvirusovis (Orf virus). J. Gen. Virol., 84(5): 1111-1116. https://doi.org/10.1099/vir.0.18850-0

Rziha, H.J., Rohde, J., Amann, R., 2016. Generation and selection of Orf virus (ORFV) recombinants. In vaccine technologies for veterinary viral diseases. Humana Press, New York, NY. pp. 177-200. https://doi.org/10.1007/978-1-4939-3008-1_12

Savory, L.J., Stacker, S.A., Fleming, S.B., Niven, B.E., and Mercer, A.A., 2000. Viral vascular endothelial growth factor plays a critical role in orf virus infection. J. Virol., 74: 10699-10706. https://doi.org/10.1128/JVI.74.22.10699-10706.2000

Schütze, N., Raue, R., Büttner, M., Alber, G., 2009. Inactivated parapoxvirusovis activates canine blood phagocytes and T lymphocytes. Vet. Microbiol., 137(3-4): 260-267. https://doi.org/10.1016/j.vetmic.2009.01.035

Seet, B.T., McCaughan, C.A., Handel, T.M., Mercer, A., Brunetti, C., et al., 2003. Analysis of an orf virus chemokine-binding protein: Shifting ligand specificities among a family of poxvirus viroceptors. Proc. Natl. Acad. Sci. U.S.A., 100(25): 15137-15142. https://doi.org/10.1073/pnas.2336648100

Seet, B.T., McFadden, G., 2002. Viral chemokine-binding proteins. J. Leukoc. Biol., 72(1): 24-34.

Shaker, M.A., Younes, H.M., 2009. Interleukin-2: Evaluation of routes of administration and current delivery systems in cancer therapy. J. Pharmacol. Sci., 98(7): 2268-2298. https://doi.org/10.1002/jps.21596

Shao, H., Robek, M.D., Threadgill, D.S., Mankowski, L.S., Cameron, C.E., et al., 1997. Characterization and mutational studies of equine infectious anemia virus dUTPase. (BBA)-Protein Struct. Mol. Enzymol., 1339(2): 181-191. https://doi.org/10.1016/S0167-4838(96)00229-4

Sharma, A.K., Dhasmana, N., Dubey, N., Kumar, N., Gangwal, A., et al., 2017. Bacterial virulence factors: secreted for survival. Indian J. Microbiol., 57(1): 1-10. https://doi.org/10.1007/s12088-016-0625-1

Siegemund, S., Hartl, A., von Buttlar, H., Dautel, F., Raue, R., et al., 2009. Conventional bone marrow-derived dendritic cells contribute to toll-like receptor-independent production of alpha/ beta interferon in response to inactivated parapoxvirusovis. J. Virol., 83(18): 9411-9422. https://doi.org/10.1128/JVI.02362-08

Son, S.J., Harris, P.W.R., Squire, C.J., Baker, E.N., Kent, S.B.H., et al., 2014. Total chemical synthesis of an orf virus protein, ORFV002, an inhibitor of the master gene regulator NF-κB. Pept. Sci., 102(2): 137-144. https://doi.org/10.1002/bip.22445

Sumner, R.P., de Motes, C.M., Veyer, D.L., Smith, G.L., 2014. Vaccinia virus inhibits NF-κB-dependent gene expression downstream of p65 translocation. J. Virol., 88(6): 3092-3102. https://doi.org/10.1128/JVI.02627-13

Tryland, M., Beckmen, K.B., Burek-Huntington, K.A., Breines, E.M., and Klein, J., 2018. Orf virus infection in Alaskan mountain goats, Dall’s sheep, muskoxen, caribou and Sitka black-tailed deer. Acta Vet. Scand., 60(1): 12. https://doi.org/10.1186/s13028-018-0366-8

Tulman, E.R., Afonso, C.L., Lu, Z., Zsak, L., Kutish, G.F., et al., 2001. Genome of lumpy skin disease virus. J. Virol., 75(15): 7122-7130. https://doi.org/10.1128/JVI.75.15.7122-7130.2001

Van Rooij, E.M.A., Rijsewijk, F.A.M., Moonen-Leusen, H.W., Bianchi, A.T.J., and Rziha, H.J., 2010. Comparison of different prime-boost regimes with DNA and recombinant Orf virus based vaccines expressing glycoprotein D of pseudorabies virus in pigs. Vaccine, 28(7): 1808-1813. https://doi.org/10.1016/j.vaccine.2009.12.004

Vertessy, B.G., Zalud, P., Nyman, P.O., and Zeppezauer, M., 1994. Identification of tyrosine as a functional residue in the active site of Escherichia coli dUTPase. (BBA)-Protein Struct. Mol. Enzymol., 1205(1): 146-150. https://doi.org/10.1016/0167-4838(94)90103-1

Vijaysri, S., Talasela, L., Mercer, A.A., Mcinnes, C.J., Jacobs, B.L., et al., 2003. The orf virus E3L homologue is able to complement deletion of the vaccinia virus E3L gene in vitro but not in vivo. Virologyk, 314(1): 305-314. https://doi.org/10.1016/S0042-6822(03)00433-1

Wagaman, P.C., Hasselkus-Light, C.S., Henson, M., Lerner, D.L., Phillips, T.R., et al., 1993. Molecular cloning and characterization of deoxyuridine triphosphatase from feline immunodeficiency virus (FIV). Virology, 196(2): 451-457. https://doi.org/10.1006/viro.1993.1501

Wang, R., Wang, Y., Liu, F., and Luo, S., 2019. Orf virus: A promising new therapeutic agent. Rev. Med. Virol., 29(1): e2013. https://doi.org/10.1002/rmv.2013

Weber, O., Siegling, A., Friebe, A., Limmer, A., Schlapp, T., et al., 2003. Inactivated parapoxvirusovis (Orf virus) has antiviral activity against hepatitis B virus and herpes simplex virus. J. Gen. Virol., 84(7): 1843-1852. https://doi.org/10.1099/vir.0.19138-0

Westphal, D., Ledgerwood, E.C., Hibma, M.H., Fleming, S.B., Whelan, E.M., et al., 2007. A novel Bcl-2-like inhibitor of apoptosis is encoded by the parapoxvirusorf virus. J. Virol., 81: 7178–7188. https://doi.org/10.1128/JVI.00404-07

Westphal, D., Ledgerwood, E.C., Tyndall, J.D., Hibma, M.H., Ueda, N., et al., 2009. The orf virus inhibitor of apoptosis functions in a Bcl-2-like manner, binding and neutralizing a set of BH3-only proteins and active Bax. Apoptosis, 14(11): 1317. https://doi.org/10.1007/s10495-009-0403-1

Wise, L.M., Savory, L.J., Dryden, N.H., Whelan, E.M., Fleming, S.B., et al., 2007. Major amino acid sequence variants of viral vascular endothelial growth factor are functionally equivalent during orf virus infection of sheepskin. Virus Res., 128: 115-125. https://doi.org/10.1016/j.virusres.2007.04.018

Wise, L.M., Stuart, G.S., Jones, N.C., Fleming, S.B., Mercer, A.A., 2020. Orf virus IL-10 and VEGF-E act synergistically to enhance healing of cutaneous wounds in mice. J. Clin. Med., 9(4): 1085. https://doi.org/10.3390/jcm9041085

Zhao, K., He, W., Gao, W., Huijun, L., Han, T., et al., 2011. Orf virus DNA vaccines expressing ORFV 011 and ORFV 059 chimeric protein enhances Immunogenicity. Virol. J., 8: 562. https://doi.org/10.1186/1743-422X-8-562