Helicobacter pylori, previously known as Campylobacter pylori, is a gram-negative, flagellated, helical bacterium. Mutants can have a rod or curved rod shape that exhibits less virulence. Its helical body (from which the genus name Helicobacter derives) is thought to have evolved to penetrate the mucous lining of the stomach, helped by its flagella, and thereby establish infection. The bacterium was first identified as the causal agent of gastric ulcers in 1983 by Australian physician-scientists Barry Marshall and Robin Warren. In 2005, they were awarded the Nobel Prize in Physiology or Medicine for their discovery. Infection of the stomach with H. pylori does not necessarily cause illness: over half of the global population is infected, but most individuals are asymptomatic. Persistent colonization with more virulent strains can induce a number of gastric and non-gastric disorders. Gastric disorders due to infection begin with gastritis, or inflammation of the stomach lining. When infection is persistent, the prolonged inflammation will become chronic gastritis. Initially, this will be non-atrophic gastritis, but the damage caused to the stomach lining can bring about the development of atrophic gastritis and ulcers within the stomach itself or the duodenum (the nearest part of the intestine). At this stage, the risk of developing gastric cancer is high. However, the development of a duodenal ulcer confers a comparatively lower risk of cancer. Helicobacter pylori are class 1 carcinogenic bacteria, and potential cancers include gastric MALT lymphoma and gastric cancer. Infection with H. pylori is responsible for an estimated 89% of all gastric cancers and is linked to the development of 5.5% of all cases cancers worldwide. H. pylori is the only bacterium known to cause cancer. Extragastric complications that have been linked to H. pylori include anemia due either to iron deficiency or vitamin B12 deficiency, diabetes mellitus, cardiovascular illness, and certain neurological disorders. An inverse association has also been claimed with H. pylori having a positive protective effect against asthma, esophageal cancer, inflammatory bowel disease (including gastroesophageal reflux disease and Crohn's disease), and others. Some studies suggest that H. pylori plays an important role in the natural stomach ecology by influencing the type of bacteria that colonize the gastrointestinal tract. Other studies suggest that non-pathogenic strains of H. pylori may beneficially normalize stomach acid secretion, and regulate appetite. In 2023, it was estimated that about two-thirds of the world's population was infected with H. pylori, being more common in developing countries. The prevalence has declined in many countries due to eradication treatments with antibiotics and proton-pump inhibitors, and with increased standards of living. Source: Wikipedia (en)