An epidermotropic canine papillomavirus with malignant potential contains an E5 gene and establishes a unique genus

Diverse papillomaviruses identified from Antarctic fur seals, leopard seals and Weddell seals from the Antarctic

Papillomaviruses (family Papillomaviridae) are non-enveloped, circular, double-stranded DNA viruses known to infect squamous and mucosal epithelial cells. In the family Papillomaviridae there are 53 genera and 133 viral species whose members infect a variety of mammalian, avian, reptilian, and fish species. Within the Antarctic context, papillomaviruses (PVs) have been identified in Adélie penguins (Pygoscelis adeliae, 2 PVs), Weddell seals (Leptonychotes weddellii, 7 PVs), and emerald notothen (Trematomus bernacchii, 1 PV) in McMurdo Sound and Ross Island in eastern Antarctica. Here we identified 13 diverse PVs from buccal swabs of Antarctic fur seals (Arctocephalus gazella, 2 PVs) and leopard seal (Hydrurga leptonyx, 3 PVs) in western Antarctica (Antarctic Peninsula), and vaginal and nasal swabs of Weddell seals (8 PVs) in McMurdo Sound. These PV genomes group into four genera representing 11 new papillomavirus types, of which five are from two Antarctic fur seals and a leopard seal and six from Weddell seals.

Exploring the link between viruses and cancer in companion animals: a comprehensive and comparative analysis

Currently, it is estimated that 15% of human neoplasms globally are caused by infectious agents, with new evidence emerging continuously. Multiple agents have been implicated in various forms of neoplasia, with viruses as the most frequent. In recent years, investigation on viral mechanisms underlying tumoral transformation in cancer development and progression are in the spotlight, both in human and veterinary oncology. Oncogenic viruses in veterinary medicine are of primary importance not only as original pathogens of pets, but also in the view of pets as models of human malignancies. Hence, this work will provide an overview of the main oncogenic viruses of companion animals, with brief notes of comparative medicine.

Canine and feline papillomaviruses: an update

Papillomaviruses are small viruses able to cause disease not only in mammalians, but also in birds and reptiles. In recent years, a rising number of papillomaviruses have been identified in dogs and cats, totaling 24 canine papillomavirus (CPV) and six feline papillomavirus (FcaPV). The canine and feline papillomaviruses (CPVs and FcaPVs, respectively) are responsible for multiple lesions in these domestic species but the potential pathological relevance of some recently identified types remains to be determined. CPVs are associated with oral papillomatosis, cutaneous papillomas and viral pigmented plaques, and have been rarely associated with the development of oral and cutaneous squamous cell carcinomas in their canine hosts. FcaPVs are associated with oral papillomas, viral plaques, and Bowenoid in situ carcinomas. The present review provides readers with the more recent advances on dog and cat papillomavirus research, bringing an update on this field to both veterinary practitioners and the virology community at large.

Long-Term Culture of Canine Ocular Cells That Maintain Canine Papillomaviruses

Canine ocular papillomas occur on the haired skin of eyelids, conjunctival epithelium, and rarely on the cornea. Using PCR typing assays with canine papillomavirus type-specific primer sets, our study confirmed that the papillomas contained canine papillomavirus type 1. The positive result from a rolling circle amplification assay indicated the CPV1 viral genome in the cells is a circular episomal form. We also successfully established the first canine corneal cell line using the conditional reprogramming method. The cells exhibited an epithelial cell morphology, grew rapidly in vitro, and could be maintained long term. For the continued growth of the canine corneal cells, feeder cells played a more important role than Rho-kinase inhibitor Y-27632. More importantly, the viral CPV1 genome was maintained in the canine corneal cells during the long-term expansion. Unlimited supplies of these cells provide as a model for the study CPV in dog cells, and a platform for drug screening for effective therapies against canine papillomavirus infection in the future.

Equus caballus Papillomavirus Type-9 (EcPV9): First Detection in Asymptomatic Italian Horses

Papillomavirus (PV) infections may be related to anogenital lesions and cancer development in humans and several other animal species. To date, 11 different PVs have been reported in horses. Among them, a newly described PV named Equus caballus Papillomavirus Type9 (EcPV9) was thus far only reported in the semen of a stallion with penile lesions in Australia. This study reports for the first time the presence of EcPV9 in asymptomatic Italian horses. From July 2020 to January 2022, genital brush samples were collected from 209 horses with no apparent signs of neoplastic disease and no PV-associated lesions, clinically examined at the Didactic Veterinary University Hospital (OVUD) of Perugia and at the Veterinary University Hospital (OVU) of Turin. Brushes were submitted to real-time PCR targeting the EcPV9-L1 region. The first amplification targeted a region of ~116 bp, followed by the amplification and sequencing of ~533 bp of the positive samples. EcPV9-L1 DNA was found in eleven horses (5.3%), all female and mainly English Thoroughbred. Co-infection with EcPV2-L1 was found in 7 out of the 11 EcPV9-L1 positive horses (63.6%). This study contributes to the description of the prevalence of exposure or infection of EcPVs in the horse population in Italy, for which data are still limited. In this regard, here we provide a phylogenetic analysis and the completely reconstructed viral genomes of two Italian EcPV type 9 isolates, as well as four EcPV type 2 obtained from co-infected animals.

Pathological Similarities in the Development of Papillomavirus-Associated Cancer in Humans, Dogs, and Cats

Simple Summary

Papillomavirus (PV) infection affects many species, including humans and domestic animals, such as dogs and cats. Some of these infections involve the development of cancer due to the presence of PV. There are similarities in the pathology of these three PV-associated cancers, which may provide crucial insights into cancer development in these species, extrapolating both markers and possible treatment in the three species. For example, the oncoproteins E5, E6, and E7 are the main causes of the development of cancer associated with PV, and the possible therapies associated with the blockage or reduction of these oncoproteins can be of great benefit for the reduction and/or elimination of cancer associated with PV. Thus, our review focuses on the similarities in the context of pathology and biomarkers in canine, feline, and human cancers associated with PV. We review the main biomarkers, E5, E6, and E7 oncoproteins, and their overexpression in Canis familiaris, Felis catus, and human papillomavirus and their association with the development of cancer. Furthermore, we also discuss that a potential treatment for PV-related cancer is the reduction or blocking of these oncoproteins.

Abstract

Canis familiaris, Felis catus, and human papillomavirus are nonenveloped viruses that share similarities in the initiation and development of cancer. For instance, the three species overexpress the oncoproteins E6 and E7, and Canis familiaris and human papillomavirus overexpress the E5 oncoprotein. These similarities in the pathophysiology of cancer among the three species are beneficial for treating cancer in dogs, cats, and humans. To our knowledge, this topic has not been reviewed so far. This review focuses on the information on cancer research in cats and dogs comparable to that being conducted in humans in the context of comparative pathology and biomarkers in canine, feline, and human cancer. We also focus on the possible benefit of treatment associated with the E5, E6, and E7 oncoproteins for cancer in dogs, cats, and humans.

New insights into Canis familiaris papillomaviruses genetics and biology: Is the genetic characterization of CPV types and their variants an important clinical issue?

Canis familiaris papillomavirus (CPV) is a member of the Papillomaviridae family and is found in dogs. After infection, the host can remain asymtomatic or develop benign ephitelial neoplasms such as papillomas and pigmented viral plaques, which can progress to cancer, in the form of squamous cell carcinoma (SCC). In humans, 227 types of human papillomavirus (HPV) have been described, with a well-established risk classification for cancer development. In addition, it is also known that variants of some high-risk HPV types may present different risks in respect of SCC development. In dogs, however, only a few types of CPV have been identified, despite the growing interest in this area, and knowledge on the genetic characterization of CPV variants is still scarce. Recent studies of CPV have shown that, as with HPV, benign neoplasia can develop into cancer, but it is believed that there are many more types and variants still to be described. Therefore, the aim of this study was to describe the genetics and biology of CPV, with the focus on what is known about lesions, geographic localization, virus types and variants.

Localization and genotyping of canine papillomavirus in canine inverted papillomas

Numerous canine papillomaviruses (CPVs) have been identified (CPV1-23). CPV1, 2, and 6 have been associated with inverted papillomas (IPs). We retrieved 19 IPs from 3 histopathology archives, and evaluated and scored koilocytes, inclusion bodies, giant keratohyalin granules, cytoplasmic pallor, ballooning degeneration, and parakeratosis. IHC targeting major capsid proteins of PV was performed, and CPV genotyping was achieved by PCR testing. Tissue localization of CPV DNA and RNA was studied by chromogenic and RNAscope in situ hybridization (DNA-CISH, RNA-ISH, respectively). IPs were localized to the limbs (50%), trunk (30%), and head (20%), mainly as single nodules (16 of 19). In 15 of 19 cases, immunopositivity was detected within the nuclei in corneal and subcorneal epidermal layers. PCR revealed CPV1 in 11 IPs and CPV2 DNA in 3 IPs. Overall, 14 of 17 cases were positive by both DNA-CISH and RNA-ISH, in accord with PCR results. A histologic score >5 was always obtained in cases in which the viral etiology was demonstrated by IHC, DNA-CISH, and RNA-ISH. IHC and molecular approaches were useful to ascertain the viral etiology of IPs. Although IHC is the first choice for diagnostic purposes, ISH testing allows identification of PV type and the infection phase. RNA-ISH seems a promising tool to deepen our understanding of the pathogenesis of different PV types in animal species.

Canine Papillomavirus 2 E6 Does Not Interfere With UVB-Induced Upregulation of p53 and p53-Regulated Genes

Cutaneous papillomaviruses are oncogenic viruses that cause severe, persistent infections that can develop into skin cancers within ultraviolet (UV)-exposed skin of immunodeficient individuals, such as those with X-linked severe combined immunodeficiency (XSCID). A canine research model of XSCID exhibits a similar phenotype; these dogs develop severe canine papillomavirus 2 (CPV2) infections that often progress to cancer. Thus, the dog is a natural, spontaneous model to investigate cutaneous papillomavirus infections in immunodeficient patients. The human papillomavirus oncogene E6 contributes to cancer development, in part, by initiating degradation of the tumor suppressor protein p53, or by inhibiting upregulation of p53-dependent genes required within the cell growth arrest and apoptotic pathways, thereby leading to an accumulation of DNA damage required for oncogenesis. Currently, little is known about CPV2, and how it promotes cancer development. The aim of this study was to determine if CPV2 oncogene E6 similarly affects p53 upon activation by UV radiation, as well as the downstream p53-regulated genes necessary to control growth arrest and apoptosis. We determined that cutaneous CPV2 E6 does not degrade p53, or interfere with the upregulation of p53-regulated genes p21, Bax, Bak, or lncRNA-p21, suggesting that CPV2 may use a p53-independent mechanism to contribute to oncogenesis.

Abrogation of Constitutive and Induced Type I and Type III Interferons and Interferon-Stimulated Genes in Keratinocytes by Canine Papillomavirus 2 E6 and E7

Cutaneous papillomaviruses can cause severe, persistent infections and skin cancer in immunodeficient patients, including people with X-linked severe combined immunodeficiency (XSCID). A similar phenotype is observed in a canine model of XSCID; these dogs acquire severe cutaneous papillomavirus infections that can progress to cancer in association with canine papillomavirus type 2 (CPV2). This canine model system provides a natural spontaneous animal model for investigation of papillomavirus infections in immunodeficient patients. Currently, it is unknown if CPV2 can subvert the innate immune system and interfere with its ability to express antiviral cytokines, which are critical in the host defense against viral pathogens. The aim of the current study was to determine if the oncogenes E6 and E7 from CPV2 interfere with expression of antiviral cytokines in keratinocytes, the target cells of papillomavirus infections. We determined that E6 but not E7 interferes with the constitutive expression of some antiviral cytokines, including interferon (IFN)-β and the IFN-stimulated gene IFIT1. Both E6 and E7 interfere with the transcriptional upregulation of the antiviral cytokines in response to stimulation with the dsDNA Poly(dA:dT). In contrast, while E6 also interferes with the transcriptional upregulation of antiviral cytokines in response to stimulation with the dsRNA Poly(I:C), E7 interferes with only a subset of these antiviral cytokines. Finally, we demonstrated that E7 but not E6 abrogates signaling through the type I IFN receptor. Taken together, CPV2 E6 and E7 both impact expression of antiviral cytokines in canine keratinocytes, albeit likely through different mechanisms.

The Detection and Association of Canine Papillomavirus with Benign and Malignant Skin Lesions in Dogs

Papillomavirus (PV) mainly infects the squamous epithelium and may potentially lead to benign or even malignant cutaneous lesions. However, the malignant transforming ability has been identified in several types of PVs. In humans, papillomavirus (HPV) type 16 and 18 are the most prevalent causative agents of cervical cancer. Therefore, vaccines are being developed to protect against these types. For dogs, there have been limited investigations into the association of different canine papillomavirus (CPV) genotypes with malignant lesions. Understanding the high-risk CPV genotype(s) responsible for these malignant lesions would contribute to the development of interventions for preventing CPV-induced carcinomas. In the present study, a retrospective cohort of 102 pathologically confirmed papillomas and 212 squamous cell carcinomas (SCCs) were included. The viral genome and antigens in the formalin-fixed paraffin-embedded (FFPE) tissues were detected using PCR targeting pan PV E1 and COPV L1 genes and by immunohistochemistry staining (IHC), respectively. PVs were successfully detected from 11 FFPE cutaneous tissues and four oral tissues using pan PV E1- and COPV L1-based PCR, respectively. After sequencing, CPV 1, CPV 2, and CPV 6 were detected in the benign lesions using PCR and were confirmed through IHC. While CPV 9 and CPV 15 were first detected in the SCCs of dogs, CPV 16 was most often detected in SCC specimens. The association and confirmative demonstration of viral genes and intralesional antigens of CPV 9, CPV 15, and CPV 16 in SCCs highlight the potential risk of these genotypes of CPVs in malignant transformation.

Malignant Transformation of a Canine Papillomavirus Type 1-Induced Persistent Oral Papilloma in a 3-Year-Old Dog

This case report describes a rare case of a persistent canine papillomavirus type 1 (CPV-1)-induced oral papilloma that underwent malignant transformation into an oral squamous cell carcinoma (OSCC) in a 3-year-old Labrador retriever cross. Initially, the patient had multiple and multifocal verrucous lesions populating the oral cavity exclusively. The papillomas persisted despite multiple surgical ablations, azithromycin, interferon α-2b, alternative medicines, and off-label drug use of an immunostimulant. After 1 year and 6 months, an aggressive lesion developed at the level of the left mandibular first molar (309) and progressed to a well-differentiated invasive OSCC. The presence of CPV-1 DNA in the OSCC, and the known oncogenic abilities of CPV-1, suggests that this virus might have played a significant role in the emergence of the OSCC that ultimately led to the patient's euthanasia due to poor quality of life. This is the first well-documented case where OSCC has developed from an oral papilloma caused by CPV-1 in which the presence of coinfection by another papillomavirus was excluded by multiple polymerase chain reaction tests using various primers.

Canine papillomavirus types 1 and 2 in classical papillomas: High abundance, different morphological associations and frequent co-infections

Canine papillomatosis is mainly attributed to papillomavirus infections. Papillomavirus DNA is also frequently identified in healthy skin, and evidence of high papillomavirus diversity complicates this simplistic view of causality. The aim of this study was to determine how frequently canine papillomas contain papillomavirus DNA and express viral protein, and how these factors correlate to the histology and anatomic location. Fifty-three archived, formalin-fixed samples of canine papillomas and eight samples of other proliferative skin lesions from dogs were included. Samples were re-evaluated histologically, tested for papillomavirus L1-antigen using immunohistochemistry, and for papillomavirus DNA with PCR assays and molecular sequencing. Most papillomas from haired skin contained papillomavirus DNA (96%) and antigen (92%). Of oral papillomas, 88% were positive for both papillomavirus DNA and antigen. Approximately 50% of non-papilloma proliferations and papillomas from eyelid/conjunctiva specimens contained viral DNA, but antigen was present in only 12% of eyelid/conjunctiva papillomas and in none of the non-papilloma proliferations. The presence of viral antigen was highly correlated with histological indicators of viral infection, including intranuclear inclusions, koilocytes, cytoplasmatic vacuolation and dysplasia. The viruses found were mainly CPV1 and CPV2. CPV1 dominated in oral infections, while CPV2 dominated in cutaneous endophytic papillomas. Co-infections with CPV1 and CPV2 accounted for about 20% of all detected infections. These results support a role for papillomaviruses in canine cutaneous and oral, exophytic and endophytic papillomas and support previously raised doubts about their role in squamous papillomas from eyelid/conjunctiva specimens.

Spontaneous regression of canine papillomavirus type 2-related papillomatosis on footpads in a dog

Persistent papillomatosis on footpads related to canine papillomavirus type 2 (CPV-2) infection has been described in dogs with immunocompromised condition. A 9-year-old, male French bulldog was presented with cauliflower-like nodules on the footpads of his left front leg. Histopathological examination revealed multiple finger-like projections of squamous epithelium with intranuclear inclusion bodies. Immunohistochemistry using an anti-bovine papillomavirus antibody demonstrated immunostaining in the keratinocytes. Partial genome DNA of CPV-2 was amplified from the lesion. Full genome sequence of CPV-2 in the subject showed 99.95% nucleotide identity with that of CPV-2 from the reference data. Two weeks after a biopsy, the skin lesion spontaneously regressed without any specific treatment. In non-immunocompromised dogs, CPV-2-related footpad papillomatosis could spontaneously resolve after a biopsy.

Viral genome integration of canine papillomavirus 16

Papillomaviruses infect humans and animals, most often causing benign proliferations on skin or mucosal surfaces. Rarely, these infections persist and progress to cancer. In humans, this transformation most often occurs with high-risk papillomaviruses, where viral integration is a critical event in carcinogenesis. The first aim of this study was to sequence the viral genome of canine papillomavirus (CPV) 16 from a pigmented viral plaque that progressed to metastatic squamous cell carcinoma in a dog. The second aim was to characterize multiple viral genomic deletions and translocations as well as host integration sites. The full viral genome was identified using a combination of PCR and high throughput sequencing. CPV16 is most closely related to chipapillomaviruses CPV4, CPV9, and CPV12 and we propose CPV16 be classified as a chipapillomavirus. Assembly of the full viral genome enabled identification of deletion of portions of the E1 and E2/E4 genes and two viral translocations within the squamous cell carcinoma. Genome walking was performed which identified four sites of viral integration into the host genome. This is the first description of integration of a canine papillomavirus into the host genome, raising the possibility that CPV16 may be a potential canine high-risk papillomavirus type.

Association of papillomavirus E6 proteins with either MAML1 or E6AP clusters E6 proteins by structure, function, and evolutionary relatedness

Papillomavirus E6 proteins bind to LXXLL peptide motifs displayed on targeted cellular proteins. Alpha genus HPV E6 proteins associate with the cellular ubiquitin ligase E6AP (UBE3A), by binding to an LXXLL peptide (ELTLQELLGEE) displayed by E6AP, thereby stimulating E6AP ubiquitin ligase activity. Beta, Gamma, and Delta genera E6 proteins bind a similar LXXLL peptide (WMSDLDDLLGS) on the cellular transcriptional co-activator MAML1 and thereby repress Notch signaling. We expressed 45 different animal and human E6 proteins from diverse papillomavirus genera to ascertain the overall preference of E6 proteins for E6AP or MAML1. E6 proteins from all HPV genera except Alpha preferentially interacted with MAML1 over E6AP. Among animal papillomaviruses, E6 proteins from certain ungulate (SsPV1 from pigs) and cetacean (porpoises and dolphins) hosts functionally resembled Alpha genus HPV by binding and targeting the degradation of E6AP. Beta genus HPV E6 proteins functionally clustered with Delta, Pi, Tau, Gamma, Chi, Mu, Lambda, Iota, Dyokappa, Rho, and Dyolambda E6 proteins to bind and repress MAML1. None of the tested E6 proteins physically and functionally interacted with both MAML1 and E6AP, indicating an evolutionary split. Further, interaction of an E6 protein was insufficient to activate degradation of E6AP, indicating that E6 proteins that target E6AP co-evolved to separately acquire both binding and triggering of ubiquitin ligase activation. E6 proteins with similar biological function clustered together in phylogenetic trees and shared structural features. This suggests that the divergence of E6 proteins from either MAML1 or E6AP binding preference is a major event in papillomavirus evolution.

Papillomaviruses in dogs and cats

Papillomaviruses (PVs) cause disease in both dogs and cats. In dogs, PVs are thought to cause oral papillomatosis, cutaneous papillomas and canine viral pigmented plaques, whereas PVs have been rarely associated with the development of oral and cutaneous squamous cell carcinomas in this species. In cats, PVs are currently thought to cause oral papillomas, feline viral plaques, Bowenoid in situ carcinomas and feline sarcoids. Furthermore, there is increasing evidence that PVs may also be a cause of cutaneous squamous cell carcinomas and basal cell carcinomas in cats. These diseases are discussed in this review. Additionally, there is a brief overview of PV biology, including how these viruses cause disease. Diagnostic techniques and possible methods to prevent PV infection are also discussed.

Genomic Sequence of Canine Papillomavirus 19

It is generally assumed that individual papillomas (warts) are caused by infection with individual papillomavirus types. Deep sequencing of virions extracted from a canine oral papilloma revealed the presence of canine papillomavirus 1 (CPV1), CPV2, and a novel canine papillomavirus, CPV19. This suggests that papillomas sometimes harbor multiple viral species.

An Update on Canine, Feline and Bovine Papillomaviruses

Over recent years, a growing number of papillomaviruses have been identified, which cause a wide range of lesions in domestic and wild animals. Papillomavirus-induced lesions may have a great impact on animal health, and some diseases observed in farm animals are associated with significant economic losses. This concise review brings together recent advancements on animal papillomavirus research, providing the scientific community and veterinary practitioners with an update on this rapidly evolving field. Among others, bovine, canine and feline papillomaviruses (BPV, CPV and FcaPV) are most extensively discussed, in view of the recent discovery of new viral types and their worldwide importance for animal health. Feline papillomaviruses 2 is an emerging, highly prevalent pathogen in domestic cats, associated with a subset of malignant skin lesions. Aspects related to cross-species infection by BPV and its environmental co-factors are also addressed. Animal papillomaviruses are also fascinating models for studying molecular and cell biology and have recently inspired some major breakthroughs. Overall, it is clear that additional, international and systematic efforts are needed to clarify which lesions are caused by which viral types and to develop experimental models for studying animal papillomavirus.

Genomic characterisation of canine papillomavirus type 17, a possible rare cause of canine oral squamous cell carcinoma

Squamous cell carcinomas (SCCs) are the second most common cancer of the canine oral cavity resulting in significant morbidity and mortality. Recently a dog with multiple oral SCCs that contained a novel papillomavirus (PV) was reported. The aim of the present study was to determine the genome of this novel PV. To do this a short section of PV DNA was amplified from an oral SCC and 'back-to-back' primers were designed. Due to the circular nature of PV DNA, these primers were then used to amplify the remainder of the genome by inverse PCR. The PCR product was sequenced using next generation sequencing and the full genome of the PV, consisting of 8007 bp, was assembled and analysed. As this is the seventeenth PV identified from the domestic dog, the novel PV was designated Canis familiaris papillomavirus (CPV) type 17. Similar to other CPV types, the putative coding regions of CPV-17 were predicted to produce 5 early and 2 late proteins. Phylogenetic analysis of ORF L1 revealed greater than 70% similarity to CPV-2 and CPV-7 and we propose that CPV-17 also be classified as a Taupapillomavirus 1. While it appears CPV-17 is only rarely present in canine oral SCCs, evidence suggests that this PV could influence the development of oral SCCs in this species.

Complete genome sequence of canine papillomavirus type 16

Papillomaviruses are epitheliotropic, circular, double-stranded DNA viruses within the family Papillomaviridae that are associated with benign and malignant tumors in humans and animals. We report the complete genome sequence of canine papillomavirus type 16 identified within multiple pigmented cutaneous plaques and squamous cell carcinoma from an intact female Basenji dog.

Complete genome sequence of canine papillomavirus virus type 12

Papillomaviruses, of the family Papillomaviridae, are epitheliotropic, nonenveloped, circular, double-stranded DNA viruses that contribute to benign and malignant tumors in humans and animals. We report here the whole-genome sequence of canine papillomavirus type 12, found at a pigmented plaque located on the skin of a mixed-breed bloodhound.

Keratinocyte antiviral response to Poly(dA:dT) stimulation and papillomavirus infection in a canine model of X-linked severe combined immunodeficiency

X-linked severe combined immunodeficiency (XSCID) is caused by a genetic mutation within the common gamma chain (γ_c), an essential component of the cytokine receptors for interleukin (IL)-2, IL-4, IL-7, IL-9, IL-15, and IL-21. XSCID patients are most commonly treated with bone marrow transplants (BMT) to restore systemic immune function. However, BMT-XSCID humans and dogs remain at an increased risk for development of cutaneous papillomavirus (PV) infections and their associated neoplasms, most typically cutaneous papillomas. Since basal keratinocytes are the target cell for the initial PV infection, we wanted to determine if canine XSCID keratinocytes have a diminished antiviral cytokine response to poly(dA:dT) and canine papillomavirus-2 (CPV-2) upon initial infection. We performed quantitative RT-PCR for antiviral cytokines and downstream interferon stimulated genes (ISG) on poly(dA:dT) stimulated and CPV-2 infected monolayer keratinocyte cultures derived from XSCID and normal control dogs. We found that XSCID keratinocytes responded similarly to poly(dA:dT) as normal keratinocytes by upregulating antiviral cytokines and ISGs. CPV-2 infection of both XSCID and normal keratinocytes did not result in upregulation of antiviral cytokines or ISGs at 2, 4, or 6 days post infection. These data suggest that the antiviral response to initial PV infection of basal keratinocytes is similar between XSCID and normal patients, and is not the likely source for the remaining immunodeficiency in XSCID patients.

Complete genome sequence of canine papillomavirus type 11

Papillomaviruses with the features of epitheliotropic, nonenveloped, circular, and double-stranded DNA belong to the family Papillomaviridae, which contributes to benign and malignant tumors in humans and animals. We report the whole-genome sequence of canine papillomavirus type 11 found at a pigmented plaque located on the skin of a mixed-breed bloodhound.

Oral papillary squamous cell carcinoma in twelve dogs

Papillary squamous cell carcinoma (PSCC) is a distinct histological subtype of oral squamous cell carcinoma (SCC), described in both dogs and man. In dogs, PSCC has long been considered a malignant oral tumour of very young animals, but it has recently been reported to occur in adult dogs as well. The aim of this study was to describe the major clinicopathological characteristics of canine oral PSCC (COPSCC). Twelve dogs diagnosed with COPSCC were included in this retrospective study (1990-2012). The majority (75%) of the dogs were >6 years of age (median age 9 years). All tumours were derived from the gingiva of dentate jaws, with 66.7% affecting the rostral aspects of the jaws. The gross appearance of the lesions varied, with one having an intraosseous component only. The majority (91.7%) of the tumours were advanced lesions (T2 and T3), but no local or distant metastases were noted. Microscopically, two patterns were seen: (1) invasion of bone forming a cup-shaped indentation in the bone or a deeply cavitating cyst within the bone (cavitating pattern), (2) histologically malignant growth, but lack of apparent bone invasion (non-cavitating pattern). The microscopical appearance corresponded to imaging findings in a majority of cases, with cavitating forms presenting with a cyst-like pattern of bone loss or an expansile mass on imaging and non-cavitating forms showing an infiltrative pattern of bone destruction on imaging. These features suggest two distinct biological behaviours of COPSCC.

Animal papillomaviruses

We provide an overview of the host range, taxonomic classification and genomic diversity of animal papillomaviruses. The complete genomes of 112 non-human papillomavirus types, recovered from 54 different host species, are currently available in GenBank. The recent characterizations of reptilian papillomaviruses extend the host range of the Papillomaviridae to include all amniotes. Although the genetically diverse papillomaviruses have a highly conserved genomic lay-out, deviations from this prototypic genome organization are observed in several animal papillomaviruses, and only the core ORFs E1, E2, L2 and L1 are present in all characterized papillomavirus genomes. The discovery of papilloma-polyoma hybrids BPCV1 and BPCV2, containing a papillomaviral late region but an early region encoding typical polyomaviral nonstructural proteins, and the detection of recombination breakpoints between the early and late coding regions of cetacean papillomaviruses, could indicate that early and late gene cassettes of papillomaviruses are relatively independent entities that can be interchanged by recombination.

Canine keratinocytes upregulate type I interferons and proinflammatory cytokines in response to poly(dA:dT) but not to canine papillomavirus

Papillomaviruses (PV) are double stranded (ds) DNA viruses that infect epithelial cells within the skin or mucosa, most often causing benign neoplasms that spontaneously regress. The immune system plays a key role in the defense against PVs. Since these viruses infect keratinocytes, we wanted to investigate the role of the keratinocyte in initiating an immune response to canine papillomavirus-2 (CPV-2) in the dog. Keratinocytes express a variety of pattern recognition receptors (PRR) to distinguish different cutaneous pathogens and initiate an immune response. We examined the mRNA expression patterns for several recently described cytosolic nucleic acid sensing PRRs in canine monolayer keratinocyte cultures using quantitative reverse transcription-polymerase chain reaction. Unstimulated normal cells were found to express mRNA for melanoma differentiation associated gene 5 (MDA5), retinoic acid-inducible gene I (RIG-I), DNA-dependent activation of interferon regulatory factors, leucine rich repeat flightless interacting protein 1, and interferon inducible gene 16 (IFI16), as well as their adaptor molecules myeloid differentiation primary response gene 88, interferon-β promoter stimulator 1, and endoplasmic reticulum-resident transmembrane protein stimulator of interferon genes. When stimulated with synthetic dsDNA [poly(dA:dT)] or dsRNA [poly(I:C)], keratinocytes responded with increased mRNA expression levels for interleukin-6, tumor necrosis factor-α, interferon-β, RIG-I, IFI16, and MDA5. There was no detectable increase in mRNA expression, however, in keratinocytes infected with CPV-2. Furthermore, CPV-2-infected keratinocytes stimulated with poly(dA:dT) and poly(I:C) showed similar mRNA expression levels for these gene products when compared with expression levels in uninfected cells. These results suggest that although canine keratinocytes contain functional PRRs that can recognize and respond to dsDNA and dsRNA ligands, they do not appear to recognize or initiate a similar response to CPV-2.

Complete genome sequence of canine papillomavirus type 10

Papillomaviruses are epitheliotropic, nonenveloped, circular, double-stranded DNA viruses within the family Papillomaviridae that are associated with benign and malignant tumors in humans and animals. We report the complete genome sequence of canine papillomavirus type 10 identified from a pigmented plaque located on the head of a mixed-breed bloodhound.

Entire genomic sequence of novel canine papillomavirus type 13

Papillomaviruses are associated with benign and malignant neoplasias of the skin and mucous membranes. The sequence of a novel canine papillomavirus was determined from DNA detected in the oral cavity of a dog. The sequence of the novel virus canine papillomavirus type 13 (CPV13) shares the highest levels of similarity with the Tau papillomaviruses CPV2 and CPV7.

Detection of six novel papillomavirus sequences within canine pigmented plaques

In dogs, papillomaviruses are thought to cause oral and cutaneous papillomas and pigmented plaques. Eight canine papillomaviruses have been fully sequenced to date. Four of these canine papillomaviruses, including Canis familiaris papillomavirus (CPV)-3, CPV-4, CPV-5, and CPV-8, were amplified from pigmented plaques. Given the identification of several different canine papillomaviruses within pigmented plaques, it is likely that there are additional papillomavirus sequences that have not been previously identified. The aim of the present study was to amplify papillomavirus DNA from pigmented plaques and identify potentially novel papillomavirus sequences through nucleotide sequence analysis. Polymerase chain reaction was used to amplify DNA sequences of the papillomavirus L1 gene from 27 pigmented plaques. Identification of novel papillomavirus sequences was based on less than 90% shared DNA homology to any known papillomavirus. DNA from 10 different papillomaviruses was identified within the pigmented plaques, including 6 putative novel papillomavirus sequences. CPV-4 was detected within 41% (11/27) of the pigmented plaques, while CPV-5 was identified within 2 pigmented plaques and CPV-3 within a single pigmented plaque. A previously identified novel papillomavirus sequence was identified within 2 pigmented plaques. The remaining 11 pigmented plaques contained 6 papillomavirus DNA sequences that have not been previously reported. These putative novel PV sequences were most similar to the canine papillomaviruses that have been detected within canine pigmented plaques.

Molecular diagnosis of a laboratory mouse papillomavirus (MusPV)

MusPV, a novel papillomavirus (PV) that naturally infects laboratory mice, was isolated and characterized from a colony of NMRI-Foxn1(nu)/Foxn1(nu) (nude) mice in India. Because MusPV may have been missed during routine pathogen screening of mice in colonies worldwide, a variety of detection methods are described to detect MusPV. The clinical and histologic lesions of productive MusPV infections fit PV-associated features, including papillomas, koilocytes within the stratum granulosum of the hyperplastic/acanthotic papillomatous epithelium, and the presence of intranuclear virus particles in koilocytotic cells visualized by electron microscopy. Antiserum against disrupted PV virions, isolated from another species (canine), identified conserved viral antigens in productively infected cells by immunohistochemistry. A rolling circle technique was used to amplify viral circular DNAs followed by endonuclease restriction enzyme digestion to determine the correct size of PV DNA. Consensus PV degenerative primers, My09/11, commonly used to detect many different types of PVs by polymerase chain reaction (PCR), particularly mucosotropic HPVs, also identified MusPV and all rodent PVs tested. Since there was one nucleotide mismatch between the My09/11 primer set and the MusPV template, a new primer set, MusPV-My09/11, was designed to specifically detect MusPV in latent infections and spontaneous MusPV-induced papillomas. Southern blot analysis verified the presence of full size PV DNA in infected tissues. Virus-like particles (VLPs), generated from MusPV L1 genes, provided a substrate for serological testing of naturally and experimentally infected mice. In summary, a series of diagnostic assays were developed and validated to detect MusPV infection in skin tumors and serological response in laboratory mice.

Complete genome sequence of canine papillomavirus type 9

Papillomaviruses are nonenveloped, double-stranded DNA viruses that are associated with both benign and malignant tumors in animals and humans. We report the complete genome sequence of canine papillomavirus type 9 isolated from a solitary pigmented plaque on a mixed-breed bloodhound.

EcPV-2 is transcriptionally active in equine SCC but only rarely detectable in swabs and semen from healthy horses

Squamous cell carcinomas (SCC) are malignant tumours arising from keratinocytes. In horses, there is increasing evidence for Equus caballus papillomavirus type 2 (EcPV-2) being causally involved in SCC development. However, only little is known regarding intralesional transcription of the virus, and sparse information on the incidence of EcPV-2 infection in healthy equids is available so far. Using RT-PCR, total mRNA from 8 EcPV-2 DNA-positive and 1 EcPV-2 negative SCC/SCC precursor lesions was screened for the presence of EcPV-2 E6 and E1 transcripts. Using PCR, we tested 193 sample specimens (30 ocular swabs, 94 genital swabs, 54 semen and 15 milk samples) from a total of 161 apparently healthy horses for the presence of EcPV-2 genes E7 and E6 or E2. Positive results were confirmed by repeating the PCR reactions, and by amplicon sequencing. E6 mRNA was detectable in 8/8 EcPV-2 DNA-positive lesions, whereas only 3/8 scored positive for E1 mRNA. EcPV-2 PCR scored positive for DNA from 1/30 ocular swabs, 4/94 genital swabs, 0/54 semen and 0/15 milk samples, thus resulting in an overall detection rate of 5/193, i.e. 2.6%. The demonstrated presence of viral mRNA in all EcPV-2 DNA-positive lesions is suggestive for an active pathogenic role of the virus in SCC development. This finding and the low incidence of EcPV-2 DNA in healthy equids further strengthen the concept of an aetiologic association of EcPV-2 with equine SCC disease.

Clinically healthy skin of dogs is a potential reservoir for canine papillomaviruses

Papillomaviruses have been linked to several skin disorders in the dog. In order to have a suitable diagnostic tool for canine papillomavirus detection, eight PCRs with published primer combinations were evaluated. The most sensitive PCR was used to demonstrate that papillomavirus DNA can be detected on nonlesional skin of dogs.

The canine papillomavirus and gamma HPV E7 proteins use an alternative domain to bind and destabilize the retinoblastoma protein

The high-risk HPV E6 and E7 proteins cooperate to immortalize primary human cervical cells and the E7 protein can independently transform fibroblasts in vitro, primarily due to its ability to associate with and degrade the retinoblastoma tumor suppressor protein, pRb. The binding of E7 to pRb is mediated by a conserved Leu-X-Cys-X-Glu (LXCXE) motif in the conserved region 2 (CR2) of E7 and this domain is both necessary and sufficient for E7/pRb association. In the current study, we report that the E7 protein of the malignancy-associated canine papillomavirus type 2 encodes an E7 protein that has serine substituted for cysteine in the LXCXE motif. In HPV, this substitution in E7 abrogates pRb binding and degradation. However, despite variation at this critical site, the canine papillomavirus E7 protein still bound and degraded pRb. Even complete deletion of the LXSXE domain of canine E7 failed to interfere with binding to pRb in vitro and in vivo. Rather, the dominant binding site for pRb mapped to the C-terminal domain of canine E7. Finally, while the CR1 and CR2 domains of HPV E7 are sufficient for degradation of pRb, the C-terminal region of canine E7 was also required for pRb degradation. Screening of HPV genome sequences revealed that the LXSXE motif of the canine E7 protein was also present in the gamma HPVs and we demonstrate that the gamma HPV-4 E7 protein also binds pRb in a similar way. It appears, therefore, that the type 2 canine PV and gamma-type HPVs not only share similar properties with respect to tissue specificity and association with immunosuppression, but also the mechanism by which their E7 proteins interact with pRb.

Human papillomaviruses (HPVs) are estimated to cause the most common sexually transmitted infection in the world, and these infections are recognized as the major cause of cervical cancer. One of the papillomavirus oncoproteins, E7, plays a major role in both the viral life cycle and progression to cancer. In cells E7 associates and inactivates pRb, a tumor suppressor protein. For the vast majority of papillomaviruses, E7 binds to pRb using a small amino acid sequence, LXCXE. However, we have now identified a papillomavirus E7 protein that lacks the LXCXE domain yet still binds and degrades pRb. This E7 protein, derived from a carcinogenic canine virus, uses its C-terminal domain to bind pRb. In addition, we discovered that a family of papillomaviruses, the gamma type HPVs, also lacks the LXCXE domain and binds pRb using a similar mechanism.

Characterization of canine oral papillomavirus by histopathological and genetic analysis in Korea

In August 2008, forty dogs out of 400 developed oral warts in a breeding farm in Korea. Canine oral papilloma infection is a common disease in dogs. However, there has been no report of an outbreak of canine oral papillomavirus (COPV) in a group of dogs or in dog breeding farms in Korea, and the genetic analysis of COPV in Korea has yet to be performed. This study diagnosed canine oral papilloma from the oral samples of these dogs based on histopathological examination and immunohistochemistry. Polymerase chain reaction was applied to amplify the corresponding products using pre-existing primer sets for COPV and a universal human papillomavirus targeting L1 gene. Further genetic analysis of the major viral capsid gene L1 confirms the sequences of Korean COPV, which shows a close relationship to previously reported COPV. This study describes the histopathological and immunohistochemical characteristics of canine oral papilloma in a group of breeding dogs in Korea and discloses the complete L1 gene sequences of Korean COPV.

Classification of papillomaviruses (PVs) based on 189 PV types and proposal of taxonomic amendments

We present an expansion of the classification of the family Papillomaviridae, which now contains 29 genera formed by 189 papillomavirus (PV) types isolated from humans (120 types), non-human mammals, birds and reptiles (64, 3 and 2 types, respectively). To accommodate the number of PV genera exceeding the Greek alphabet, the prefix "dyo" is used, continuing after the Omega-PVs with Dyodelta-PVs. The current set of human PVs is contained within five genera, whereas mammalian, avian and reptile PVs are contained within 20, 3 and 1 genera, respectively. We propose standardizations to the names of a number of animal PVs. As prerequisite for a coherent nomenclature of animal PVs, we propose founding a reference center for animal PVs. We discuss that based on emerging species concepts derived from genome sequences, PV types could be promoted to the taxonomic level of species, but we do not recommend implementing this change at the current time.

Papillomavirus-Associated Cutaneous Neoplasia in Mammals

For humans, strong evidence indicates that some mucosal papillomavirus (PV) types cause genital and oral neoplasia, and weaker evidence suggests that some cutaneous PVs may cause cutaneous squamous cell carcinomas (SCC). For nonhuman species, strong evidence supports a causal role of PVs in the development of feline and equine sarcoids. Likewise, PVs are believed to cause cutaneous SCCs in rabbits, western barred bandicoots, and some rodents. Furthermore, some evidence suggests that PVs may influence the development of both feline and canine cutaneous SCCs. This review discusses the evidence that PVs cause human cutaneous SCCs and the proposed mechanisms for this action. It then reviews preneoplastic and neoplastic skin diseases that are associated with PV infection in nonhuman mammals.

Three novel canine papillomaviruses support taxonomic clade formation

More than 100 human papillomaviruses (HPVs) have been identified and had their whole genomes sequenced. Most of these HPVs can be classified into three distinct genera, the alpha-, beta- and gamma-papillomaviruses (PVs). Of note, only one or a small number of PVs have been identified for each individual animal species. However, four canine PVs (CPVs) (COPV, CPV2, CPV3 and CPV4) have been described and their entire genomic sequences have been published. Based on their sequence similarities, they belong to three distinct clades. In the present study, circular viral DNA was amplified from three dogs showing signs of pigmented plaques, endophytic papilloma or in situ squamous cell carcinoma. Analysis of the DNA sequences suggested that these are three novel viruses (CPV5, CPV6 and CPV7) whose genomes comprise all the conserved sequence elements of known PVs. The genomes of these seven CPVs were compared in order properly classify them. Interestingly, phylogenetic analyses, as well as pairwise sequence alignments of the putative amino acid sequences, revealed that CPV5 grouped well with CPV3 and CPV4, whereas CPV7 grouped with CPV2 but neither group fitted with other classified PVs. However, CPV6 grouped with COPV, a lambda-PV. Based on this evidence, allocation of CPVs into three distinct clades could therefore be supported. Thus, similar to HPVs, it might be that the known and currently unknown CPVs are related and form just a few clades or genera.