FREE SHIPPING over $40
OVER 10000 FIVE-STAR REVIEWS
5% OFF ALL SUBSCRIPTIONS
100% HAPPINESS GUARANTEE
Analyze Diet
0
Equine veterinary journal2026; doi: 10.1002/evj.70311

Genetic variants of EcPV2 E6 and E7 in equine genital and oronasal squamous cell carcinoma.

Abstract: Since its discovery in 2008, equine papillomavirus type 2 (EcPV2) has been detected in up to 100% of equine genital and up to 40% of equine oronasal squamous cell carcinomas (SCCs). Preliminary sequence data point to the existence of EcPV2 E6 and E7 oncogene variants compared to the British reference sequence from 2008. Objective: To Identify E6 and E7 sequence variations in EcPV2-positive tumours of horses from Continental Europe and Iceland. Methods: Cross-sectional study. Methods: EcPV2 E6 and E7 were amplified from DNA of 60 EcPV2-positive SCCs/SCC precursor lesions. Amplicons were gel-purified and submitted to bidirectional Sanger sequencing. Resulting 5'-and 3'-sequences were aligned with each other and then to EcPV2 sequences in the GenBank to determine sequence variations on DNA and predicted protein level. Results: Eight E6 gene variants were identified, predicting four E6 protein variants compared to the reference sequence. One E6 variant predominantly occurred in Icelandic horses imported from Iceland. Detected genetic variations in E6 were unlikely to affect known functional motifs. The E7 gene was highly conserved. None to three SNPs were detected per lesion, and only one E7 sequence contained a SNP predicted to be non-synonymous. Conclusions: Low number of oronasal SCCs (n = 10) included in the study. Conclusions: The detected E6 and E7 variants point to the existence of different EcPV2 sublineages. Interestingly, one E6-E7 sequence was significantly associated with SCC-bearing Icelandic horses imported from Iceland, suggesting that a specific EcPV2 sublineage may have evolved on the island. Provided that this theory can be confirmed, the long period between initial EcPV2 infection in Iceland and tumour development would indicate that EcPV2 can induce chronic infections that are reactivated in the older horse. Obtained sequence data are currently implemented in the generation of an immunotherapeutic vaccine targeting EcPV2 E6 and E7.
© 2026 The Author(s). Equine Veterinary Journal published by John Wiley & Sons Ltd on behalf of EVJ Ltd.
Get Full Text
Publication Date: 2026-08-19 PubMed ID: 42615548DOI: 10.1002/evj.70311Google Scholar: Lookup
The Equine Research Bank provides access to a large database of publicly available scientific literature. Inclusion in the Research Bank does not imply endorsement of study methods or findings by Mad Barn.
LinkedInCopy
  • Journal Article

Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

Overview

  • This study investigated genetic variations in the E6 and E7 oncogenes of equine papillomavirus type 2 (EcPV2) found in squamous cell carcinomas (SCCs) from horses, particularly focusing on horses from Continental Europe and Iceland.
  • The research aimed to identify viral gene variants that could relate to tumor development and potentially inform future immunotherapy treatments.

Introduction to the Research

  • EcPV2 and Its Significance: Equine papillomavirus type 2 (EcPV2) was first identified in 2008.
  • Association with Cancer: EcPV2 DNA has been found in almost all equine genital SCCs (up to 100%) and about 40% of oronasal SCCs, which are cancers affecting the nasal and oral regions in horses.
  • Genes of Interest: E6 and E7 are oncogenes (cancer-causing genes) in papillomaviruses known to interfere with cell cycle regulation, making their variations important in tumor biology.
  • Background Gap: Initial sequencing from a British reference strain hinted that EcPV2 E6 and E7 genes might have variants in different geographical or clinical contexts.

Objectives

  • To characterize the genetic variation of EcPV2 E6 and E7 genes in tumors from horses in Continental Europe and Iceland.
  • To determine if specific variants correlate with geographical origin or tumor types.
  • To infer potential implications for viral evolution and tumor development.

Methods

  • Sample Collection: DNA was extracted from 60 EcPV2-positive squamous cell carcinomas or precursor lesions.
  • Molecular Techniques: The E6 and E7 genes were amplified using PCR.
  • Sequencing: The amplified gene fragments were purified and sequenced using bidirectional Sanger sequencing for accuracy.
  • Data Analysis: The 5’ and 3’ sequences were aligned for consistency and compared to known EcPV2 sequences from GenBank.
  • Variant Identification: Changes at the DNA level (single nucleotide polymorphisms or SNPs) and predicted changes in the protein sequences of E6 and E7 were determined.

Results

  • E6 Gene Variants: Eight different E6 gene variants were found.
  • E6 Protein Variants: These nucleotide changes predicted four distinct protein variants of E6 compared to the original 2008 reference.
  • Geographic Association: One particular E6 variant was strongly associated with Icelandic horses imported from Iceland, pointing to a region-specific viral sublineage.
  • Functional Impact: The variations within E6 did not appear to disrupt known functional motifs important for the virus’s oncogenic activity.
  • E7 Gene Conservation: E7 showed very little genetic variability; up to three SNPs were found in some lesions, but only one mutation was predicted to cause an amino acid change, indicating high conservation.
  • Sample Size Note: Only 10 oronasal SCC samples were included, which is a relatively low number for this group.

Conclusions and Implications

  • Sublineages Exist: The presence of multiple E6 and E7 variants suggests that different EcPV2 sublineages circulate among horse populations.
  • Evolution on Iceland: The association of a unique E6-E7 variant with Icelandic horses suggests viral evolution in geographic isolation, possibly on the Icelandic island.
  • Chronic Infection Hypothesis: The time lag between initial infection (likely occurring in Iceland) and tumor development supports the idea that EcPV2 may cause chronic infections that remain dormant or reactivate later in the horse’s life.
  • Vaccine Development: The characterization of these variants is contributing to the development of an immunotherapeutic vaccine targeting EcPV2 E6 and E7 proteins, aiming to treat or prevent associated cancers in horses.

Significance of the Study

  • Improves understanding of EcPV2 genetic diversity and its link to cancer in horses.
  • Highlights geographic and evolutionary viral differences that may influence disease outcomes.
  • Supports the development of targeted therapies by defining viral variants that can be used as vaccine targets.
  • Offers insights into the natural history of viral infection and oncogenesis in equine species.

Cite This Article

APA
Jenner M, Brandt S. (2026). Genetic variants of EcPV2 E6 and E7 in equine genital and oronasal squamous cell carcinoma. Equine Vet J. https://doi.org/10.1002/evj.70311

Publication

Equine veterinary journal
ISSN: 2042-3306
NlmUniqueID: 0173320
Country: United States
Language: English

Researcher Affiliations

Jenner, Maya
  • Research Group Oncology (RGO), Division of Equine Surgery, Centre for Equine Health and Research, University of Veterinary Medicine, Vienna, Austria.
Brandt, Sabine
  • Research Group Oncology (RGO), Division of Equine Surgery, Centre for Equine Health and Research, University of Veterinary Medicine, Vienna, Austria.

References

This article includes 53 references
  1. Dayyani F, Etzel CJ, Liu M, Ho CH, Lippman SM, Tsao AS. Meta‐analysis of the impact of human papillomavirus (HPV) on cancer risk and overall survival in head and neck squamous cell carcinomas (HNSCC).. Head Neck Oncol 2010;2:15.
    doi: 10.1186/1758-3284-2-15google scholar: lookup
  2. Scott DW, Miller WH Jr. Squamous cell carcinoma.. In: Scott DW, Miller WH Jr, editors. Equine dermatology. 1st ed. St. Louis, MI: Saunders Elsevier; 2003. p. 707–712.
  3. Cohen EEW, Bell RB, Bifulco CB, Burtness B, Gillison ML, Harrington KJ. The Society for Immunotherapy of Cancer consensus statement on immunotherapy for the treatment of squamous cell carcinoma of the head and neck (HNSCC).. J Immunother Cancer 2019;7(1):184.
    doi: 10.1186/s40425-019-0662-5google scholar: lookup
  4. Munoz N. Human papillomavirus and cancer: the epidemiological evidence.. J Clin Virol 2000;19(1–2):1–5.
  5. zur Hausen H. Papillomavirus infections—a major cause of human cancers.. Biochim Biophys Acta 1996;1288(2):F55–F78.
  6. Scase T, Brandt S, Kainzbauer C, Sykora S, Bijmholt S, Hughes K. Equus caballus papillomavirus‐2 (EcPV‐2): an infectious cause for equine genital cancer?. Equine Vet J 2010;42(8):738–745.
    doi: 10.1111/j.2042-3306.2010.00311.xgoogle scholar: lookup
  7. Armando F, Mecocci S, Orlandi V, Porcellato I, Cappelli K, Mechelli L. Investigation of the epithelial to mesenchymal transition (EMT) process in equine papillomavirus‐2 (EcPV‐2)‐positive penile squamous cell carcinomas.. Int J Mol Sci 2021;22(19):10588.
    doi: 10.3390/ijms221910588google scholar: lookup
  8. Bogaert L, Willemsen A, Vanderstraeten E, Bracho MA, de Baere C, Bravo IG. EcPV2 DNA in equine genital squamous cell carcinomas and normal genital mucosa.. Vet Microbiol 2012;158(1–2):33–41.
    doi: 10.1016/j.vetmic.2012.02.005google scholar: lookup
  9. Brandt S, Samek L, Sykora S, Scase T. Association of EcPV‐2 with equine squamous cell carcinoma.. Vet Comp Oncol 2013;11(3):e26.
  10. da Silva TRO, Goncalves PNC, Marcus VB, Mucellini CI, Santos IRD, Kommers G. Detection of Equus caballus papillomavirus‐2 in equine penile/preputial papillomas and squamous cell carcinomas in southern Brazil.. Braz J Microbiol 2022;53(3):1707–1713.
    doi: 10.1007/s42770-022-00769-3google scholar: lookup
  11. Fischer NM, Favrot C, Birkmann K, Jackson M, Schwarzwald CC, Müller M. Serum antibodies and DNA indicate a high prevalence of equine papillomavirus 2 (EcPV2) among horses in Switzerland.. Vet Dermatol 2014;25(3):210–214, e53–4.
    doi: 10.1111/vde.12129google scholar: lookup
  12. Greenwood S, Chow‐Lockerbie B, Epp T, Knight C, Wachoski‐Dark G, MacDonald‐Dickinson V. Prevalence and prognostic impact of Equus caballus papillomavirus type 2 infection in equine squamous cell carcinomas in Western Canadian horses.. Vet Pathol 2020;57(5):623–631.
    doi: 10.1177/0300985820941266google scholar: lookup
  13. Knight CG, Dunowska M, Munday JS, Peters‐Kennedy J, Rosa BV. Comparison of the levels of Equus caballus papillomavirus type 2 (EcPV‐2) DNA in equine squamous cell carcinomas and non‐cancerous tissues using quantitative PCR.. Vet Microbiol 2013;166(1–2):257–262.
    doi: 10.1016/j.vetmic.2013.06.004google scholar: lookup
  14. Lange CE, Tobler K, Lehner A, Grest P, Welle MM, Schwarzwald CC. EcPV2 DNA in equine papillomas and in situ and invasive squamous cell carcinomas supports papillomavirus etiology.. Vet Pathol 2013;50(4):686–692.
    doi: 10.1177/0300985812463403google scholar: lookup
  15. Newkirk KM, Hendrix DV, Anis EA, Hendrix DVH, Rohrbach BW, Ehrhart EJ. Detection of papillomavirus in equine periocular and penile squamous cell carcinoma.. J Vet Diagn Invest 2014;26(1):131–135.
    doi: 10.1177/1040638713511618google scholar: lookup
  16. Ramsauer AS, Kubacki J, Favrot C, Ackermann M, Fraefel C, Tobler K. RNA‐seq analysis in equine papillomavirus type 2‐positive carcinomas identifies affected pathways and potential cancer markers as well as viral gene expression and splicing events. J Gen Virol 2019;100(6):985–998.
    doi: 10.1099/jgv.0.001267google scholar: lookup
  17. Sykora S, Jindra C, Hofer M, Steinborn R, Brandt S. Equine papillomavirus type 2: an equine equivalent to human papillomavirus 16?. Vet J 2017;225:3–8.
    doi: 10.1016/j.tvjl.2017.04.014google scholar: lookup
  18. Luff J, Weingart S, May S, Murphy B. A subset of equine oral squamous cell carcinomas is associated with Equus caballus papillomavirus 2 infection. J Comp Pathol 2023;205:1–6.
    doi: 10.1016/j.jcpa.2023.06.003google scholar: lookup
  19. Ramsauer AS, Wachoski‐Dark GL, Fraefel C, Ackermann M, Brandt S, Grest P. Establishment of a three‐dimensional in vitro model of equine papillomavirus type 2 infection. Viruses 2021;13(7):1404.
    doi: 10.3390/v13071404google scholar: lookup
  20. Ramsauer AS, Wachoski‐Dark GL, Fraefel C, Tobler K, Brandt S, Knight CG. Paving the way for more precise diagnosis of EcPV2‐associated equine penile lesions. BMC Vet Res 2019;15(1):356.
    doi: 10.1186/s12917-019-2097-0google scholar: lookup
  21. Sykora S, Samek L, Schonthaler K, Palm F, Borzacchiello G, Aurich C. EcPV‐2 is transcriptionally active in equine SCC but only rarely detectable in swabs and semen from healthy horses. Vet Microbiol 2012;158(1–2):194–198.
    doi: 10.1016/j.vetmic.2012.02.006google scholar: lookup
  22. Wise‐Draper TM, Wells SI. Papillomavirus E6 and E7 proteins and their cellular targets. Front Biosci 2008;13:1003–1017.
  23. Gardiol D, Kuhne C, Glaunsinger B, Lee SS, Javier R, Banks L. Oncogenic human papillomavirus E6 proteins target the discs large tumour suppressor for proteasome‐mediated degradation. Oncogene 1999;18(40):5487–5496.
    doi: 10.1038/sj.onc.1202920google scholar: lookup
  24. Pim D, Bergant M, Boon SS, Ganti K, Kranjec C, Massimi P. Human papillomaviruses and the specificity of PDZ domain targeting. FEBS J 2012;279(19):3530–3537.
    doi: 10.1111/j.1742-4658.2012.08709.xgoogle scholar: lookup
  25. Bernard HU, Burk RD, Chen Z, van Doorslaer K, zur Hausen H, de Villiers EM. Classification of papillomaviruses (PVs) based on 189 PV types and proposal of taxonomic amendments. Virology 2010;401(1):70–79.
    doi: 10.1016/j.virol.2010.02.002google scholar: lookup
  26. Yamada T, Wheeler CM, Halpern AL, Stewart AC, Hildesheim A, Jenison SA. Human papillomavirus type 16 variant lineages in United States populations characterized by nucleotide sequence analysis of the E6, L2, and L1 coding segments. J Virol 1995;69(12):7743–7753.
    doi: 10.1128/jvi.69.12.7743-7753.1995google scholar: lookup
  27. Chakrabarti O, Veeraraghavalu K, Tergaonkar V, Liu Y, Androphy EJ, Stanley MA. Human papillomavirus type 16 E6 amino acid 83 variants enhance E6‐mediated MAPK signaling and differentially regulate tumorigenesis by notch signaling and oncogenic Ras. J Virol 2004;78(11):5934–5945.
    doi: 10.1128/jvi.78.11.5934-5945.2004google scholar: lookup
  28. Hoffmann M, Lohrey C, Hunziker A, Kahn T, Schwarz E. Human papillomavirus type 16 E6 and E7 genotypes in head‐and‐neck carcinomas. Oral Oncol 2004;40(5):520–524.
    doi: 10.1016/j.oraloncology.2003.10.011google scholar: lookup
  29. Wichmann G. Variation of HPV subtypes with focus on HPV‐infection and cancer in the head and neck region. Recent Results Cancer Res 2017;206:113–122.
    doi: 10.1007/978-3-319-43580-0_8google scholar: lookup
  30. Kainzbauer C, Rushton J, Tober R, Scase T, Nell B, Sykora S. Bovine papillomavirus type 1 and Equus caballus papillomavirus 2 in equine squamous cell carcinoma of the head and neck in a Connemara mare. Equine Vet J 2012;44(1):112–115.
    doi: 10.1111/j.2042-3306.2010.00358.xgoogle scholar: lookup
  31. Brandt S, Haralambus R, Schoster A, Kirnbauer R, Stanek C. Peripheral blood mononuclear cells represent a reservoir of bovine papillomavirus DNA in sarcoid‐affected equines.. J Gen Virol 2008;89(Pt 6):1390–1395.
    doi: 10.1099/vir.0.83568-0google scholar: lookup
  32. Lale D, Geyer A, Jindra C, Cavalleri J-MV, Ramsauer AS. Equine papillomavirus type 2‐associated, carcinomatous lesions of the penis and laryngopharynx of an elderly Icelandic horse gelding.. Vet Rec Case Rep 2023;11:e508.
    doi: 10.1002/vrc2.508google scholar: lookup
  33. Curik I, Druml T, Seltenhammer M, Sundström E, Pielberg GR, Andersson L. Complex inheritance of melanoma and pigmentation of coat and skin in Grey horses.. PLoS Genet 2013;9(2):e1003248.
    doi: 10.1371/journal.pgen.1003248google scholar: lookup
  34. Chambers G, Ellsmore VA, O'Brien PM, Reid SWJ, Love S, Campo MS. Association of bovine papillomavirus with the equine sarcoid.. J Gen Virol 2003;84(Pt 5):1055–1062.
    doi: 10.1099/vir.0.18947-0google scholar: lookup
  35. Zhu KW, Affolter VK, Gaynor AM, Dela Cruz FN Jr, Pesavento PA. Equine genital squamous cell carcinoma: in situ hybridization identifies a distinct subset containing Equus caballus papillomavirus 2.. Vet Pathol 2015;52(6):1067–1072.
    doi: 10.1177/0300985815583095google scholar: lookup
  36. Hibi H, Hatama S, Obata A, Shibahara T, Kadota K. Laryngeal squamous cell carcinoma and papilloma associated with Equus caballus papillomavirus 2 in a horse.. J Vet Med Sci 2019;81(7):1029–1033.
    doi: 10.1292/jvms.18-0461google scholar: lookup
  37. Strohmayer C, Klang A, Kummer S, Walter I, Jindra C, Weissenbacher-Lang C. Tumor cell plasticity in equine papillomavirus‐positive versus‐negative squamous cell carcinoma of the head and neck.. Pathogens 2022;11(2):266.
    doi: 10.3390/pathogens11020266google scholar: lookup
  38. Armando F, Godizzi F, Razzuoli E, Leonardi F, Angelone M, Corradi A. Epithelial to mesenchymal transition (EMT) in a laryngeal squamous cell carcinoma of a horse: future perspectives.. Animals 2020;10(12):2318.
    doi: 10.3390/ani10122318google scholar: lookup
  39. Sykora S, Brandt S. Papillomavirus infection and squamous cell carcinoma in horses.. Vet J 2017;223:48–54.
  40. Bosch FX, Burchell AN, Schiffman M, Giuliano AR, de Sanjose S, Bruni L. Epidemiology and natural history of human papillomavirus infections and type‐specific implications in cervical neoplasia.. Vaccine 2008;26(Suppl 10):K1–K16.
    doi: 10.1016/j.vaccine.2008.05.064google scholar: lookup
  41. Bosch FX, De Sanjosé S, Castellsagué X, Moreno V, Muños N. Epidemiology of human papillomavirus infections and associations with cervical cancer: new opportunities for prevention.. In: Campo MS, editor. Papillomavirus research: from natural history to vaccines and beyond. 1st ed. Norfolk: Caister Academic Press; 2006. p. 19–39.
  42. Koch C, Ramsauer AS, Drogemuller M, Ackermann M, Gerber V, Tobler K. Genomic comparison of bovine papillomavirus 1 isolates from bovine, equine and asinine lesional tissue samples.. Virus Res 2018;244:6–12.
    doi: 10.1016/j.virusres.2017.11.005google scholar: lookup
  43. Austrian Working Group for the Breeding of the Haflinger. ARGE Haflinger. Available from: https://www.pferdezucht-austria.at/main.asp?kat1=107&kat2=2798&kat3=676
  44. Chen Z, Terai M, Fu L, Herrero R, DeSalle R, Burk RD. Diversifying selection in human papillomavirus type 16 lineages based on complete genome analyses.. J Virol 2005;79(11):7014–7023.
    doi: 10.1128/jvi.79.11.7014-7023.2005google scholar: lookup
  45. Chow LT, Broker TR. Mechanisms and regulation of papillomavirus DNA replication.. In: Campo MS, editor. Papillomavirus research: from natural history to vaccines and beyond. 1st ed. Norfol: Caister Academic Press; 2006. p. 53–71.
  46. Burk RD, Chen Z, Van Doorslaer K. Human papillomaviruses: genetic basis of carcinogenicity. Public Health Genomics 2009;12(5–6):281–290.
    doi: 10.1159/000214919google scholar: lookup
  47. Burk RD, Harari A, Chen Z. Human papillomavirus genome variants. Virology 2013;445(1–2):232–243.
    doi: 10.1016/j.virol.2013.07.018google scholar: lookup
  48. Rector A, Lemey P, Tachezy R, Mostmans S, Ghim SJ, van Doorslaer K. Ancient papillomavirus‐host co‐speciation in Felidae. Genome Biol 2007;8(4):R57.
    doi: 10.1186/gb-2007-8-4-r57google scholar: lookup
  49. Schwarz E, Freese UK, Gissmann L, Mayer W, Roggenbuck B, Stremlau A. Structure and transcription of human papillomavirus sequences in cervical carcinoma cells. Nature 1985;314(6006):111–114.
    doi: 10.1038/314111a0google scholar: lookup
  50. Thomas M, Pim D, Banks L. The role of HPV E6 oncoprotein in malignant progression. 2006. p. 115–132.
  51. Wang J, Zhou D, Prabhu A, Schlegel R, Yuan H. The canine papillomavirus and gamma HPV E7 proteins use an alternative domain to bind and destabilize the retinoblastoma protein. PLoS Pathog 2010;6(9):e1001089.
    doi: 10.1371/journal.ppat.1001089google scholar: lookup
  52. Jindra C, Hainisch EK, Rummele A, Wolschek M, Muster T, Brandt S. Influenza virus vector iNS1 expressing bovine papillomavirus 1 (BPV1) antigens efficiently induces tumour regression in equine sarcoid patients. PLoS One 2021;16(11):e0260155.
    doi: 10.1371/journal.pone.0260155google scholar: lookup
  53. Hainisch EK, Jindra C, Brandt S. Live‐attenuated influenza virus co‐expressing BPV1 E6 and E7 antigens as an adjuvant treatment to surgery for cases of severe sarcoid disease in horses. Trieste: ICGEB; 2024. p. 57.

Citations

This article has been cited 0 times.
Subscribe to our newsletter
Join 106,698 horse owners like you who receive our email updates on horse health and nutrition.