A novel kirkovirus may be associated with equine gastrointestinal disease.
Abstract: Many cases of equine enterocolitis are suspected to be infectious in nature, but no pathogen is identified in many cases. Objective: Perform next-generation sequencing on faeces collected from cases of equine enterocolitis for the presence of novel viruses and determine if an identified novel virus is associated with cases of equine enterocolitis. Methods: Retrospective cohort study. Methods: Next generation sequencing was performed targeting viral genomes from n = 13 pooled faecal samples (n = 5 horses/pool) with enterocolitis. Subsequent qPCR was performed targeting the highly conserved replication-associated segment of the identified kirkovirus genome on n = 218 samples (collected between 2020 and 2025), divided into 3 groups [colitis (n = 87), colic (n = 56) and clinically normal (n = 75)]. Additional qPCR was performed on a subset of cases targeting the less well-conserved open reading frame 3 (ORF3) segment of the kirkovirus genome. In situ hybridisation and electron microscopy on kirkovirus-positive samples were also performed. Results: Next generation sequencing identified a novel kirkovirus in 5/13 pooled samples from enterocolitis cases, including the full genome. There was an association between the novel kirkovirus and enterocolitis, specifically in two farm outbreaks. A retrospective case review of kirkovirus-positive cases suggested a seasonal pattern, with all cases presented in the autumn, winter, and spring. Additionally, there was an association with small colon impactions, with 25% of positive cases having a small colon impaction. Conclusions: Whether equine kirkovirus is a cause of equine infectious enterocolitis remains unknown. There are limited available tissue samples from positive horses and efforts to definitively identify equine kirkovirus in the gastrointestinal tract tissues have been unsuccessful. Conclusions: We identified a novel equine kirkovirus that is associated with outbreaks of enterocolitis and small colon impactions. It is rarely identified in clinically normal populations. Further study must be performed to determine if the virus infects equine tissues and/or causes disease.
© 2025 The Author(s). Equine Veterinary Journal published by John Wiley & Sons Ltd on behalf of EVJ Ltd.
Publication Date: 2025-11-14 PubMed ID: 41236343PubMed Central: PMC12892396DOI: 10.1111/evj.70121Google Scholar: Lookup
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- Journal Article
Summary
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Overview
- This research identified a new virus, called kirkovirus, which may be linked to gastrointestinal illness in horses.
- The study investigated the presence of this virus in horses with enterocolitis and explored its potential association with disease outbreaks.
Background and Objective
- Equine enterocolitis, a disease causing inflammation of the intestines in horses, is often suspected to be caused by infectious agents.
- However, in many cases no specific pathogen (disease-causing organism) is identified using standard diagnostics.
- The objective was to use next-generation sequencing (NGS) to detect any novel viruses present in fecal samples from horses with enterocolitis.
- The study aimed to determine if any newly identified virus is associated with disease cases.
Methods
- Sample Collection:
- Thirteen pooled fecal samples (each pool from 5 horses) with enterocolitis were analyzed via NGS.
- A total of 218 individual samples, collected from 2020 to 2025, were tested. These were separated into three groups:
- Colitis cases (87 samples)
- Colic cases (56 samples)
- Clinically normal horses (75 samples)
- Next-Generation Sequencing:
- Targeted detection of viral genomes was performed on pooled fecal samples to identify novel viral sequences.
- Quantitative PCR (qPCR):
- Performed to detect the kirkovirus genome’s replication-associated segment that is highly conserved among viruses in this group.
- Additional qPCR targeted a less conserved gene segment (ORF3), potentially to confirm virus identity and detect variants.
- Further Analyses:
- In situ hybridization was used to localize viral genetic material within tissue samples, aiming to identify infected tissues.
- Electron microscopy was performed on virus-positive samples to visualize viral particles.
Results
- NGS Findings:
- A novel kirkovirus was detected in 5 out of 13 pooled samples from horses with enterocolitis, with the full viral genome sequenced.
- Association With Disease:
- The novel kirkovirus was found in two distinct farm outbreaks of equine enterocolitis, indicating a possible epidemiological link.
- There was a statistically notable occurrence of the virus in horses with enterocolitis compared to clinically normal horses.
- Seasonal Pattern:
- Review of cases showed all positive cases occurred in autumn, winter, and spring, suggesting seasonal influences on infection or disease manifestation.
- Correlation With Gastrointestinal Conditions:
- One quarter (25%) of horses positive for kirkovirus had small colon impactions, potentially indicating a clinical complication linked with infection.
- Tissue Analysis:
- Attempts to definitively locate the virus in gastrointestinal tissues through in situ hybridization were unsuccessful, possibly due to limited tissue availability or low viral load.
Conclusions and Implications
- The study identified a previously unknown virus, equine kirkovirus, associated with outbreaks of equine enterocolitis and small colon impactions.
- The virus is rarely found in horses without clinical signs, suggesting potential involvement in disease.
- Despite the association, it remains unclear whether kirkovirus causes the gastrointestinal disease or is merely present due to other factors.
- Current evidence is limited by the lack of successful detection of the virus in tissue samples, leaving its role in infection and pathogenesis uncertain.
- Further research is needed to:
- Confirm whether kirkovirus infects equine gastrointestinal tissues directly.
- Determine if the virus causes disease or contributes to pathogenesis.
- Understand the epidemiology and transmission of kirkovirus in horse populations.
Cite This Article
APA
Haywood LMB, Clark A, Hause B, Sheahan B.
(2025).
A novel kirkovirus may be associated with equine gastrointestinal disease.
Equine Vet J, 58(2), 414-422.
https://doi.org/10.1111/evj.70121 Publication
Researcher Affiliations
- Department of Clinical Sciences, College of Veterinary Medicine, North Carolina State University, Raleigh, North Carolina, USA.
- Department of Biological Sciences, North Carolina State University, Raleigh, North Carolina, USA.
- Cambridge Technologies, Worthington, Minnesota, USA.
- Department of Clinical Sciences, College of Veterinary Medicine, North Carolina State University, Raleigh, North Carolina, USA.
MeSH Terms
- Horses
- Animals
- Horse Diseases / virology
- Retrospective Studies
- Feces / virology
- Herpesviridae / genetics
- Herpesviridae / isolation & purification
- Herpesviridae / classification
- Enterocolitis / veterinary
- Enterocolitis / virology
- Gastrointestinal Diseases / virology
- Gastrointestinal Diseases / veterinary
- Herpesviridae Infections / veterinary
- Herpesviridae Infections / virology
- Genome, Viral
Grant Funding
- North Carolina State University College of Veterinary Medicine Competitive Research Grants Program
- 536126 / North Carolina Horse Council
Conflict of Interest Statement
Dr. Ben Hause is the Chief Scientific Officer at Cambridge Technologies which performed the Next Generation Sequencing.
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