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Veterinary research2025; 56(1); 12; doi: 10.1186/s13567-024-01434-3

Genomic analysis and replication kinetics of the closely related EHV-1 neuropathogenic 21P40 and abortigenic 97P70 strains.

Abstract: Varicellovirus equidalpha 1, formerly known as Equid alphaherpesvirus 1 (EHV-1), is highly prevalent and can lead to various problems, such as respiratory problems, abortion, neonatal foal death, and neurological disorders. The latter is known as equine herpes myeloencephalopathy (EHM). Cases of EHM have significantly increased since the beginning of the twenty-first century. The genomic sequences of five isolates associated with the fatal neurological outbreak in Valencia, Spain, in 2021 were analyzed and documented. The genome and replication kinetics of the Belgian EHM isolate 21P40, associated with the Valencia outbreak, and the well-characterized abortigenic strain 97P70 were compared. Both strains exhibited a nucleotide identity of 99.96%, with only seven genetic mutations in ORFs 13, 24, 30, 32, 40, 65, and 71. Isoleucine and asparagine at loci 291 and 207 of ORF30 (DNA polymerase) and ORF65 (ICP22), respectively, were unique to isolates from the Valencia outbreak. The replication kinetics of these two genetically closely related strains were determined in rabbit kidney (RK-13), equine respiratory, and vaginal mucosal explant cells, as well as equine blood monocytes (CD172a). Both strains replicated equally well in RK-13 cells. The neuropathogenic isolate 21P40 exhibited a more extensive infection in respiratory explants and blood monocytes, as demonstrated by more plaques and single infected leukocytes, and a higher percentage of infected monocytes. In contrast, vaginal explants infected with the abortigenic strain 97P70 demonstrated more plaques and single infected leukocytes. In conclusion, 21P40 replicated significantly different compared to 97P70 but shared similarities with the Belgian well-studied neuropathogenic EHV-1 strain 03P37.
© 2025. The Author(s).
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Publication Date: 2025-01-13 PubMed ID: 39806433PubMed Central: PMC11731145DOI: 10.1186/s13567-024-01434-3Google Scholar: Lookup
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  • 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 research compares the genetic makeup and replication behavior of two closely related strains of Equid alphaherpesvirus 1 (EHV-1), one associated with neurological disease outbreaks and the other with abortion in horses.
  • The study aims to understand genetic differences and replication patterns that could explain variations in disease outcomes caused by these viral strains.

Background

  • Equid alphaherpesvirus 1 (EHV-1) is a common virus affecting horses worldwide.
  • EHV-1 infections can cause respiratory illness, abortion during pregnancy, death of newborn foals, and neurological disease known as equine herpes myeloencephalopathy (EHM).
  • There has been a notable rise in EHM cases since the early 2000s.
  • The study focuses on two strains: the neuropathogenic 21P40 strain linked to a fatal neurological outbreak in Valencia, Spain in 2021, and the abortigenic strain 97P70, known for causing abortions.

Genomic Analysis

  • Researchers sequenced the genomes of five viral isolates from the 2021 Valencia EHM outbreak.
  • The genomes of strain 21P40 (neuropathogenic) and 97P70 (abortigenic) were compared.
  • Both strains showed 99.96% nucleotide identity, indicating they are extremely similar genetically.
  • Only seven mutations were found in specific open reading frames (ORFs 13, 24, 30, 32, 40, 65, and 71).
  • Unique amino acid changes were identified in ORF30 (DNA polymerase) and ORF65 (ICP22) associated with the neuropathogenic Valencia isolates:
    • Isoleucine at position 291 in ORF30
    • Asparagine at position 207 in ORF65
  • These mutations may be linked to the neuropathogenic properties of the 21P40 strain.

Replication Kinetics Study

  • Replication of 21P40 and 97P70 was tested in various cell types relevant to infection:
    • Rabbit kidney cells (RK-13)
    • Equine respiratory mucosal explants
    • Equine vaginal mucosal explants
    • Equine blood monocytes (CD172a+)
  • Findings:
    • Both strains replicated similarly in RK-13 cells, showing equal growth in this non-equine cell line.
    • In equine respiratory explants and blood monocytes, the neuropathogenic strain 21P40 caused more infection, indicated by more plaques, more infected leukocytes, and a higher percentage of infected monocytes.
    • Conversely, the 97P70 abortigenic strain showed higher replication in vaginal mucosal explants.

Conclusions and Implications

  • Despite high genetic similarity, 21P40 and 97P70 demonstrate significant differences in how they replicate in different equine tissues.
  • The unique genetic mutations in the neuropathogenic strain may help explain its enhanced ability to infect respiratory tissue and blood immune cells, which could contribute to neurological disease development.
  • The abortigenic strain’s preference for vaginal tissue replication aligns with its role in causing abortion.
  • The neuropathogenic strain 21P40 shares replication characteristics with another known Belgian neuropathogenic strain (03P37), supporting the idea of specific viral traits linked to disease outcomes.
  • Understanding these differences at the genomic and replication levels is crucial for developing targeted prevention and treatment strategies for EHV-1 associated diseases, including EHM and abortion in horses.

Cite This Article

APA
Mohamed E, Zarak I, Vereecke N, Theuns S, Laval K, Nauwynck H. (2025). Genomic analysis and replication kinetics of the closely related EHV-1 neuropathogenic 21P40 and abortigenic 97P70 strains. Vet Res, 56(1), 12. https://doi.org/10.1186/s13567-024-01434-3

Publication

Veterinary research
ISSN: 1297-9716
NlmUniqueID: 9309551
Country: England
Language: English
Volume: 56
Issue: 1
Pages: 12
PII: 12

Researcher Affiliations

Mohamed, Eslam
  • Department of Translational Physiology, Infectiology and Public Health, Faculty of Veterinary Medicine, Ghent University, 9820, Merelbeke, Belgium. eslam.elhanafy@ugent.be.
  • Department of Animal Medicine, Faculty of Veterinary Medicine, Benha University, Moshtohor, 13736, Egypt. eslam.elhanafy@ugent.be.
Zarak, Ines
  • Department of Translational Physiology, Infectiology and Public Health, Faculty of Veterinary Medicine, Ghent University, 9820, Merelbeke, Belgium.
Vereecke, Nick
  • Department of Translational Physiology, Infectiology and Public Health, Faculty of Veterinary Medicine, Ghent University, 9820, Merelbeke, Belgium.
  • PathoSense BV, Pastoriestraat 10, 2500, Lier, Belgium.
Theuns, Sebastiaan
  • PathoSense BV, Pastoriestraat 10, 2500, Lier, Belgium.
Laval, Kathlyn
  • Department of Translational Physiology, Infectiology and Public Health, Faculty of Veterinary Medicine, Ghent University, 9820, Merelbeke, Belgium.
Nauwynck, Hans
  • Department of Translational Physiology, Infectiology and Public Health, Faculty of Veterinary Medicine, Ghent University, 9820, Merelbeke, Belgium.

MeSH Terms

  • Herpesvirus 1, Equid / physiology
  • Herpesvirus 1, Equid / genetics
  • Horses
  • Animals
  • Horse Diseases / virology
  • Horse Diseases / epidemiology
  • Virus Replication
  • Herpesviridae Infections / veterinary
  • Herpesviridae Infections / virology
  • Herpesviridae Infections / epidemiology
  • Genome, Viral
  • Spain / epidemiology
  • Rabbits
  • Kinetics
  • Female

Grant Funding

  • GOA013-17 / Universiteit Gent
  • G035920N / Fonds Wetenschappelijk Onderzoek
  • PhD Scholarship / Ministry of Higher Education
  • HBC.2020.2889 / Agentschap Innoveren en Ondernemen

Conflict of Interest Statement

Declarations. Competing interests: The authors declare that they have no competing interests.

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Citations

This article has been cited 3 times.
  1. Conn KL. Equine histones are mobilized within equid alphaherpesvirus 1 (EHV1) replication compartments. J Virol 2025 Dec 23;99(12):e0158925.
    doi: 10.1128/jvi.01589-25pubmed: 41288450google scholar: lookup
  2. Mohamed E, Van Cleemput J, Şahin B, Van den Broeck W, Boyen F, Nauwynck H. Streptococcus equi subsp. zooepidemicus Supernatant Containing Streptolysin S Alters the Equine Nasal and Vaginal Mucosa, Modulating Equine Herpesvirus 1, 3 and 4 Infections. Viruses 2025 Jul 14;17(7).
    doi: 10.3390/v17070980pubmed: 40733597google scholar: lookup
  3. Mohamed E, Zarak I, Vereecke N, Theuns S, Laval K, Nauwynck H. Correction: Genomic analysis and replication kinetics of the closely related EHV-1 neuropathogenic 21P40 and abortigenic 97P70 strains. Vet Res 2025 Feb 7;56(1):34.
    doi: 10.1186/s13567-025-01464-5pubmed: 39920827google scholar: lookup
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