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''Helicobacter pylori'', previously ''Campylobacter pylori'', is a Gram-negative, microaerophilic bacterium found in the stomach, and may be present in other parts of the body, such as the eye. It was identified in 1982 by Australian scientists Barry Marshall and Robin Warren, who found that it was present in a person with chronic gastritis and gastric ulcers, conditions not previously believed to have a microbial cause. It is also linked to the development of duodenal ulcers and stomach cancer. However, over 80% of individuals infected with the bacterium are asymptomatic and it may play an important role in the natural stomach ecology. More than 50% of the world's population harbor ''H. pylori'' in their upper gastrointestinal tract. Infection is more prevalent in developing countries, and incidence is decreasing in Western countries. ''H. pylori's'' helical shape (from which the genus name is derived) is thought to have evolved to penetrate the mucoid lining of the stomach. ==Signs and symptoms== Up to 85% of people infected with ''H. pylori'' never experience symptoms or complications. Acute infection may appear as an acute gastritis with abdominal pain (stomach ache) or nausea. Where this develops into chronic gastritis, the symptoms, if present, are often those of non-ulcer dyspepsia: stomach pains, nausea, bloating, belching, and sometimes vomiting or black stool. Individuals infected with ''H. pylori'' have a 10 to 20% lifetime risk of developing peptic ulcers and a 1 to 2% risk of acquiring stomach cancer. Inflammation of the pyloric antrum is more likely to lead to duodenal ulcers, while inflammation of the corpus (body of the stomach) is more likely to lead to gastric ulcers and gastric carcinoma. However, ''H. pylori'' possibly plays a role only in the first stage that leads to common chronic inflammation, but not in further stages leading to carcinogenesis.〔 A meta-analysis conducted in 2009 concluded the eradication of ''H. pylori'' reduces gastric cancer risk in previously infected individuals, suggesting the continued presence of ''H. pylori'' constitutes a relative risk factor of 65% for gastric cancers; in terms of absolute risk, the increase was from 1.1% to 1.7%. ''H. pylori'' has also been associated with colorectal polyps and colorectal cancer. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「helicobacter pylori」の詳細全文を読む スポンサード リンク
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