Infectious gastritis (excluding helicobacter)

Because of the high acid content of the normal stomach, the gastric environment is inhospitable to most infectious agents. However, in patients with atrophic gastritis and decreased acid secretion, in patients with impaired immune responses, or as part of systemic infections, numerous viruses, bacteria, and parasites can infect the stomach. Although rare, some of these infectious gastritides have characteristic clinical and pathological features.

Viruses

Enteric rotaviruses and caliciviruses probably infect the stomach during the course of gastroenteritis, but no pathological changes in the gastric mucosa have been documented in volunteer studies with these agents. Only cytomegalovirus (CMV) infection is known to have a distinct pathological appearance in the stomach. CMV gastritis is seen almost exclusively in young children and immunocompromised patients, and it is usually associated with concurrent CMV infection of other sites of the digestive tract. Endoscopically, the gastric mucosa may appear completely normal or may show erosions, shallow ulcers, or hemorrhagic gastritis. Rarely, the condition may present as grossly nodular mucosa that has been referred to as a pseudotumor. CMV inclusions may be abundant and thus easily detected using the routine hematoxylin and eosin stain, or they may be rare and impossible to demonstrate without using immunohistochemi­stry or in situ hybridization techniques. A characteristic manifestation of CMV infection in the stomach of young children is massive foveolar hyperplasia accompanied by edema and mild inflammation of the lamina propria. The resulting endoscopic appearance is that of a giant-fold hypertrophic gastropathy indistinguishable from Ménétrier disease.

The diagnosis of gastric CMV infection is made by demonstrating the characteristic nuclear or cytoplasmic viral inclusions. The only effective therapeutic agent is ganciclovir, a guanosine derivative that selectively inhibits CMV DNA polymerase. In patients with acquired immunodeficiency syndrome (AIDS) and CMV colitis, ganciclovir has a response rate of 70% to 90%.

Bacteria

Bacterial overgrowth may occur in stomachs that have become achlorhydric as a result of atrophy, complete antrectomy, or vagotomy or as a result of long-term use of histamine H 2-receptor antagonists or proton pump inhibitors. Patients with scleroderma and other severe motility impairments are also prone to bacterial overgrowth. In contrast to H.pylori, however, these bacteria colonize rather than infect the gastric mucosa, and they neither elicit inflammatory responses nor cause symptoms.

An extremely rare condition is acute suppurative gastritis, also known as phlegmonous gastritis. This life-threatening condition is caused by pyogenic bacteria (streptococci, staphylococci, Escherichia coli, Proteus, and Haemophilus spp.) and is characterized by large areas of purulent necrosis involving the full thickness of the gastric wall. When it is caused by gas-forming organisms, the term emphysematous gastritis has been used. Few cases have been reported, mostly in very young children, elderly persons, patients with alcoholism, and immunocompromised patients. Potential iatrogenic causes include polypectomy and mucosal injection with India ink. The diagnosis is made endoscopically or at surgery. Antibiotic treatment may have to be accompanied by surgical intervention.

Primary gastric tuberculosis is rare, particularly in industrialized countries. However, in patients with disseminated tuberculosis, necrotizing granulomata may be found in the gastric mucosa. Another Mycobacterium that has gained prominence with the spread of AIDS is Mycobacterium avium-intracellulare complex, but the stomach is rarely involved; when it is, typical lesions consist of accumulations of foamy histiocytes in the lamina propria, sometimes with formation of ill-defined granulomata without necrosis.

In the 1980s and early 1990s, increasing numbers of cases of gastric syphilis were reported in patients infected with human immunodeficiency virus. When associated with secondary syphilis, syphilitic gastritis is characterized by a prominent mixed inflammatory infiltrate consisting predominantly of plasma cells and with mucosal ulcerations. The infiltrate may be dense enough to cause the swelling of gastric folds, which may also undergo erosion and ulceration, sometimes mimicking the endoscopic appearance of lymphoma or infiltrating carcinoma. Symptoms include severe dyspepsia, nausea, vomiting, and anorexia, with rapid weight loss. The diagnosis is often delayed by a low index of suspicion. Although spirochetes may be seen in sections stained with appropriate silver stains (Dieterle, Steiner, or Warthin-Starry), the search may be painstaking and is usually beyond the reach of the nonspecialist pathologist. Standard treatment for secondary syphilis is rapidly effective.

Fungi

Candida species, Histoplasmacapsulatum, and Mucoraceae have been found in the stomach of immunocompromised patients, particularly those with AIDS, with disseminated infections, but none of these fungi have been reported as a primary cause of gastritis.

Parasites

The stomach is not a preferred site for human parasitic infections, but Cryptosporidium spp. and Giardia intestinalis have been identified in the gastric mucosa. Strongyloidesstercoralis has been found in the stomach of a few patients with widespread infections.

The only nematodes that invade the human gastric wall are those of the family collectively known as Anisakidae, or “sushi worms.” Anisakiasis is an important cause of morbidity in countries such as Japan, where large quantities of raw fish are consumed. The muscle of many species of edible fishes contain larvae of Anisakidae. In a small proportion of persons who eat infected fish, larvae penetrate the gastric wall and cause a sudden onset of epigastric pain. Because the worms can be easily removed endoscopically by an experienced operator and the disease is self-limited in any case, patients presenting with epigastric pain in high-prevalence countries should be asked routinely about ingestion of raw or undercooked fish within 12 hours before the onset of symptoms. This practice would help to avoid unnecessary surgery.