A previously unknown virus linked to bowel cancer has been discovered

Scientists from Denmark have discovered that the gut bacterium Bacteroides fragilis may harbor an unknown virus linked to colorectal cancer. The results of the study have been published in the journal Communications Medicine (ComMed).

According to the researchers' estimates, up to 80% of cases are associated with environmental factors. The gut microbiome — the collection of bacteria, fungi, and viruses living in the digestive tract — also plays an important role.

The bacterium Bacteroides fragilis is generally considered a common and relatively harmless inhabitant of the gut. However, scientists have repeatedly observed that the numbers of these organisms are elevated in people with cancer.

Initially, scientists hypothesized that the "cancer-associated" bacteria might belong to a separate evolutionary lineage, but this hypothesis was not confirmed. The researchers then focused on genetic elements that bacteria can acquire externally — for example, through infection by viruses.

As a result, two previously unknown prophages — viruses integrated into bacterial DNA — were discovered in the genomes of bacteria from cancer patients. Such viruses were virtually absent in bacteria from the guts of healthy individuals.

To verify the results, the scientists analyzed stool samples from 877 people across Europe, the United States, and Asia. Among them, 434 had colorectal cancer and 443 did not. It turned out that patients with bowel cancer were more than twice as likely to have these viral elements detected.

The authors emphasize that this is only a statistical association. It is not yet known whether the viruses contribute to cancer development or, conversely, whether the characteristics of the gut environment during the disease create conditions favorable for such bacteria.

Nevertheless, the discovery may have practical significance. The researchers suggest that viral "signatures" in the microbiome could be used for early detection of bowel cancer. Preliminary analysis showed that a test for genome fragments of these viruses is capable of detecting approximately 40% of disease cases.