Mtu

Plasma cell

Red blood cell Ulcer

Dilated capillary

Cellular response to inflammation

606 Chapter 24 Alimentary System Infections

Table 24.2 Helicobacter pylori Gastritis

Symptoms

Initial infection: range from belching to vomiting. Localized abdominal pain and tenderness, bleeding when complicated by ulcer or cancer

Incubation period

Usually undetermined

Causative agent

Helicobacter pylori, a spiral Gram-negative microaerophilic bacterium, with sheathed flagella

Pathogenesis

Organisms survive the acidity of stomach juices by producing a powerful urease. Upon reaching the layer of mucus, they penetrate to the epithelial surface, where bacterial products incite an inflammatory response.Thinning of the mucus layer occurs, and 10 to 20% of infected individuals develop ulcerations. Only a small percentage develop cancer, but more than 90% of individuals with stomach cancers are infected with H. pylori

Epidemiology

Probably fecal-oral transmission. Progressive increase with age, reaching almost 80% of those over 75

Prevention and treatment

No proven preventive. Most infections are cured using two antibiotics together, plus a medication to suppress stomach acid

peptic ulcers of the stomach and duodenum. A very small percentage of individuals infected with H. pylori develop cancer of the stomach, but more than 90% of those with stomach cancer are infected by the bacterium. Virulent H. pylori strains produce a protein, CagA, which they inject into host cells, resulting in changes in shape and surface characteristics of the cells. Evidence suggests these changes represent a prelude to malignancy. Another bacterial product, VacA, acts on mucosal cells to promote flow of urea into the stomach.

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