When Helicobacter pylori was identified in the stomach mucosa, its presence was shown to cause gastritis, peptic ulcers, and cancer. As a result, the bacterium was classified as definitively harmful, and its eradication became a mandatory therapeutic indication. Subsequent studies showed that (i) eradication of the bacterium was associated with reflux esophagitis and esophageal cancer; (ii) in African, Indian, Asian, and even European populations of the last century, the presence of the bacterium was not associated with gastritis, peptic ulcers, and cancer; and (iii) the presence of H. pylori had some beneficial effects. Further studies revealed that the harmful effects of H. pylori do not occur when intestinal worms are present.

These data suggest that a simple analysis of the association of H. pylori presence with certain pathologies is incomplete and misleading. Conversely, in the interpretation of evolutionary medicine, it is necessary to consider the interactions between H. pylori and other components of the human holobiont (i.e., human species, plus the species coexisting with it). An alteration in the ancestral relationships among the components of the human holobiont, for example by elimination of one or more species considered pathogenic, represents a cause of holobiont imbalance with plausible negative effects on the host's health.

The eradication of intestinal worms or H. pylori, or both, and the concomitant alteration of microbial ecosystems of the human holobiont are a plausible cause of harmful and even lethal diseases that are increasingly widespread in the modern world.