<unk> , previously known as Campylobacter<unk> , is a gram-negative, microaerophilic, spiral (helical) bacterium usually found in the stomach. Its helical shape (from which the genus name,<unk> , derives) is thought to have evolved in order to penetrate the mucoid lining of the stomach and thereby establish infection. The bacterium was first identified in 1982 by the Australian doctors Barry Marshall and Robin Warren.<unk>  has been associated with lymphomas of the mucosa-associated lymphoid tissue in the stomach, esophagus, colon, rectum, or tissues around the eye (termed extranodal marginal zone B-cell lymphoma of the cited organ), and of lymphoid tissue in the stomach (termed diffuse large B-cell lymphoma).<unk>  infection usually has no symptoms but sometimes causes gastritis (stomach inflammation) or ulcers of the stomach or first part of the small intestine. The infection is also associated with the development of certain cancers. Many investigators have suggested that<unk>  causes or prevents a wide range of other diseases, but many of these relationships remain controversial. Some studies suggest that<unk>  plays an important role in the natural stomach ecology, e.g. by influencing the type of bacteria that colonize the gastrointestinal tract. Other studies suggest that non-pathogenic strains of<unk>  may beneficially normalize stomach acid secretion, and regulate appetite. In 2015, it was estimated that over 50% of the world's population had<unk>  in their upper gastrointestinal tracts with this infection (or colonization) being more common in developing countries. In recent decades, however, the prevalence of<unk>  colonization of the gastrointestinal tract has declined in many countries.
Helicobacter pylori
Giardia duodenalis
Entamoeba histolytica
Neisseria mucosa
Cryptosporidium parvum
Entamoeba gingivalis
Campylobacter upsaliensis
Ancylostoma duodenale