Previously unknown virus in common gut bacterium found more often in colorectal cancer patients
Feb 22nd 2026
Researchers identified a new bacteriophage in Bacteroides fragilis that appears roughly twice as often in people with colorectal cancer, but the study shows association not causation.
- Researchers at the University of Southern Denmark and Odense University Hospital discovered a previously undescribed virus that infects Bacteroides fragilis.
- The virus was found about twice as often in stool samples from colorectal cancer patients across datasets from Europe, the US and Asia.
- The initial signal came from Danish patients with bloodstream infections by Bacteroides fragilis and genomic comparison of bacterial samples.
- The study demonstrates a statistical association but cannot show that the virus causes colorectal cancer.
- Selected viral sequences identified around 40 percent of cancer cases in preliminary analyses while being uncommon in healthy individuals.
- Follow-up experiments include artificial gut models, direct tumour tissue testing, and mouse studies to explore mechanism and causality.
- Findings are published in Communications Medicine and are still preliminary, so further research is required before any clinical screening use.