Infectious Diseases

Novel Virus May Be Associated With Colitis

By Tracey Peake

Researchers from North Carolina State University have found a novel kirkovirus that may be associated with colitis—and potentially small colon impactions—in horses.

The results of this pilot study could offer a route to new therapies for horses with colitis symptoms from unknown causes, the researchers said.

“Horses are uniquely susceptible to colitis, and the structure of their gastrointestinal tracts amplify the negative effects,” said Lilly Haywood, PhD, a student in NC State’s College of Veterinary Medicine and the first author of the study. “Horses have very large colons and cecums to facilitate water absorption, so when these structures become inflamed the horses dehydrate quickly. And their large intestines contain a lot of bacteria, so inflammation can lead to those bacteria entering the bloodstream and causing sepsis.”

Researchers suspect that many cases of equine enterocolitis are infectious, but no pathogen is identified in many cases, according to Branna Sheahan, DVM, PhD, an assistant professor of equine medicine at NC State and the corresponding author. “The other issue when dealing with colitis in horses is that in more than 50% of cases we are unable to find the cause,” she said. “We suspected there might be another viral cause for some of these cases, so we started looking for one.”

The researchers began by performing metagenomic sequencing on fecal samples from 65 horses with enterocolitis that were divided into 13 pools of 5. The sequencing identified a novel kirkovirus—a virus found in various livestock animals and potentially associated with GI diseases like enterocolitis—in 1 of the sampling pools, which contained 5 horses from the same farm. They also found evidence of the kirkovirus in 5 of the remaining 12 pools of samples.

Next, they performed targeted quantitative polymerase chain reaction (qPCR) for kirkovirus on 218 fecal samples collected between 2020 and 2025, divided into 3 groups: colitis (n = 87), colic (n = 56) and clinically normal (n = 75). The qPCR identified the kirkovirus in 24% of the colitis group, 5.4% of the colic group and 6.7% of the normal group.

Most affected horses in the colitis group were from 2 farms that had experienced farm-wide outbreaks of GI disease. Additionally, the researchers saw that 25% of the kirkovirus cases also had small colon impactions, which typically are rare.

“The first step to developing therapeutics is identifying the pathogen,” Dr. Sheahan said. “While we can’t definitively say that this novel kirkovirus was responsible for the illness, this work does identify a potential culprit in some cases, particularly because of the association between the virus and small colon impactions. Next steps for this work will be to find out whether kirkovirus infects the cells of the equine gastrointestinal tract.”

The study was supported by the North Carolina Horse Council 536126 and an intramural grant from the NC State University College of Veterinary Medicine Competitive Research Grants Program. MeV

This article first appeared on the NC State website. It has been edited for length and style. https://news.ncsu.edu/2025/12/novel-kirkovirus-may-be-associated-with-colitis-in-horses/

For more information:
Haywood LMB, Clark A, Hause B, et al. A novel kirkovirus may be associated with equine gastrointestinal disease. Equine Vet J. 2025 Nov. 18 DOI: 10.1111/evj.70121
https://beva.onlinelibrary.wiley.com/doi/pdfdirect/10.1111/evj.70121