Helicobacter Infection in Small Animals
Helicobacter spp are commonly found in the stomachs of both healthy and vomiting dogs and cats, but their significance is not well defined. Although H pylori infections in people have been linked to gastritis, peptic ulcers, and a higher rate of gastric neoplasia, similar direct casual relationships between Helicobacter infections and GI disease have not been established in dogs and cats.
Helicobacter organisms are spiral or curved, gram-negative, motile, flagellated organisms. H pylori is the most commonly reported species in human GI infections, but non-H pylori organisms (such as H felis, H heilmannii, and H bizzozeronii) are more common in dogs and cats. At least 38 different Helicobacter species have been identified in animals, and infected animals can harbor multiple species.
Helicobacter organisms have been identified most commonly in the gastric tissue of dogs and cats, especially in the fundus and cardia of the stomach, but they are also found in the intestinal tract. Colonization of gastric mucosa appears to be most prevalent in the surface mucus layer, as well as within the gastric glands and parietal cells. There have been sporadic reports of Helicobacter organisms identified in the hepatic tissue of a dog with multifocal necrotizing hepatitis, as well as in healthy cats and in cats with cholangiohepatitis.
Transmission of Helicobacter infections between groups of dogs or cats is unclear, and reservoir hosts have not been defined. Because of the increased rate of morbidity and mortality associated with Helicobacter infections in people, concern of zoonotic transmission has been raised (see below).
Studies report as many as 100% of healthy dogs and cats are positive for Helicobacter infections; similar infection rates are reported in vomiting dogs and cats. In people, H pylori infection is associated with gastritis, peptic ulcers, and an increased risk of gastric neoplasia. Gastritis, vomiting, and diarrhea have been associated with Helicobacter infection, although a direct causal relationship has not been identified. Peptic ulceration is rarely associated with Helicobacter infections in dogs and cats.
Diagnosis involves upper GI endoscopy or exploratory laparotomy. Surface mucus from a large area of the stomach can be obtained by taking brush samples via endoscopy. If organisms are present, they are readily identified under 100× oil-immersion magnification. Because brush cytology samples a large area of the stomach, the sensitivity of this test is high.
Gastric biopsies should be obtained from multiple areas in the stomach, because organism distribution can be patchy. Routine H&E staining is usually sufficient to identify organisms, although special silver stains may be required if the organisms have a glandular location. Mucosal inflammation, glandular degeneration, and lymphoid follicle hyperplasia accompany some infections. Cytology and histopathology is not sufficient to identify specific species. A commercially available rapid urease test to detect production of bacterial urease in gastric biopsies can identify the presence of Helicobacter organisms. However, because cytology and histopathology are highly sensitive and specific for detection of Helicobacter infections, urease testing may not add further diagnostic information in some cases.
Noninvasive tests for Helicobacter infection available in the research setting include urea breath testing, fecal antigen detection, and serology.
The lack of knowledge regarding the pathogenicity of Helicobacter infections in dogs and cats makes treatment decisions difficult. H pylori infections in people are treated with double or triple antimicrobial agent therapy plus an acid secretory inhibitor (eg, clarithromycin, amoxicillin, bismuth, and ranitidine) for 2 wk, and similar therapeutic approaches have been used in veterinary medicine.
Currently, the role of Helicobacter as a causative agent of gastritis in dogs and cats is unclear. Treatment decisions for dogs and cats should be based on presence of Helicobacter, in combination with appropriate clinical signs and/or gastric lesions. In many veterinary studies, Helicobacter infections have been difficult to eradicate. Recommended treatment regimens include amoxicillin or tetracycline, metronidazole, bismuth subsalicylate, and a proton pump inhibitor (eg, omeprazole) or H2-receptor blocker (eg, famotidine) for 2–3 wk. Other treatment combinations of omeprazole and azithromycin or clarithromycin have been described. Although many dogs and cats treated with the above combinations did not experience longterm eradication of Helicobacter infection, when retested, the frequency of vomiting and gastric lesions did improve with therapy for many patients.
Zoonotic transmission of Helicobacter infections from dogs and cats to people is possible. H canis, H felis, H heilmannii, and other species naturally colonize the stomachs of dogs and cats, and these strains of Helicobacter have been linked to gastritis, ulcers, and lymphoma in people. Whereas many strains of Helicobacter in dogs and cats are genetically distinct from those implicated in human infections, at least one case report documents a genetically identical strain of H heilmannii infecting pet dogs and a child in the same house. Although some studies have suggested a higher risk of Helicobacter infection in people in contact with dogs and cats, other research refutes this. Given the unknown risk of transmission, proper hygiene practices are encouraged, and identification of infections in dogs and cats with chronic gastritis and vomiting is likely prudent.