Researchers at North Carolina State University have been investigating a novel kirkovirus that could be linked to colitis and small colon impactions in horses. More than half of infectious equine colitis cases do not have a determined etiology, the authors reported. They used next generation sequencing to evaluate feces from horses with gastrointestinal disease and identified kirkovirus. This single-strand DNA virus has been identified in many mammals besides horses, including swine, calves, adult cows, sheep, donkeys, and children with early type 1 diabetes.
Study: PCR Testing for Kirkovirus
In this study, the researchers performed fecal sampling on equine cases of gastrointestinal (GI) disease from four different sources in North Carolina. The 65 horses sick with colitis had diarrhea and at least two other abnormalities: fever, endotoxemia signs, or colonic wall thickening on ultrasound.
Metagenomic sequencing confirmed this novel kirkovirus was more closely related to donkey and porcine kirkovirus rather than “a previously reported equine kirkovirus.”
The researchers performed PCR testing for kirkovirus on 214 horse samples (collected between 2020-2025):
- Of 87 colitis cases, 24.1% (21 horses) were positive for kirkovirus.
- Of 56 colic cases, 5.4% (3 horses) were positive for kirkovirus.
- Of 75 normal horses, 6.7% (5 horses) were positive for kirkovirus.
Most of the positive horses came from three farms, two of which had farmwide outbreaks of GI disease. When those three farms were removed from the analysis, 3 out of 55 colitis (5.5%), 2 out of 55 colic (3.6%), and 2 out of 55 normal (3.6%) samples were positive for kirkovirus.
Of the 28 horses that tested positive for kirkovirus, 25% (7 horses) had small colon impaction, which is considered unusual.
On one of the two farms with GI disease outbreaks, 7 out of 8 (87.5%) horses tested positive for kirkovirus but negative for Salmonella, Clostridioides difficile, and equine coronavirus. On the other GI-affected farm, 55% of horses were positive for kirkovirus, but six of the kirkovirus-positive horses also had equine coronavirus, and two had salmonellosis.
Take-Home Message
While half of colitis cases have no identified etiology, the authors suggest that “kirkovirus may represent one such pathogen, or it may be shed more often when the GI microbiome is altered.” They identified the novel kirkovirus in feces from 28 horses; of these, 21 had colitis or GI disease on a farm with a GI disease outbreak.
The positive fecal samples were collected between September and April, with the highest percentage of positives found in January. This implies a possible higher incidence in cooler weather.
A retrospective evaluation of medical records shows that kirkovirus-positive horses displayed systemic illness with signs of tachycardia, tachypnea, neutropenia, and hyperglycemia. Some also had small colon impaction and diarrhea. The authors noted that these nonspecific clinical signs are linked to other possible infectious diseases. However, this outbreak was a short time frame (three weeks), with horses testing negative for other infectious agents while also experiencing small colon impaction. Small colon impaction typically occurs in only 2.5% of equine colic cases.
In conclusion, the authors stated: “We propose that equine kirkovirus may be a relevant virus in outbreaks of gastrointestinal disease where small colon impactions are a feature. Concurrent infections with multiple enteric pathogens may occur and should be considered in the diagnostic assessment of clinical cases.” At this time and based on this study, they have not yet been able to demonstrate that kirkovirus infects the equine GI tract, and they suggest more studies to evaluate the virus’s potential to infect equine enterocytes in cell culture.
Reference
Haywood LMB, Clark A, Hause B, Sheahan B. A novel Kirkovirus may be associated with equine gastrointestinal disease. Equine Veterinary Journal Nov 2025; DOI: 10.1111/evj.70121
Related Reading
- Cola Might Help Treat Gastric Impactions in Horses
- The Hindgut’s Role in Racehorse Health
- Researchers Identify Risk Factors for Postpartum Colic in Broodmares
Stay in the know! Sign up for EquiManagement’s FREE weekly newsletters to get the latest equine research, disease alerts, and vet practice updates delivered straight to your inbox.
