The role of Helicobacter species in newly recognized gastrointestinal tract diseases of animals.

Because Helicobacter pylori is now known to be a significant human pathogen, experimental animal models are increasingly being used to study the pathogenesis of this organism. Unfortunately, early studies failed to establish H. pylori in animal models, and surprisingly, Koch's postulates were initially fulfilled in two human volunteers. Germfree experiments performed in pigs and pups however established that H. pylori would colonize in these animals, and gastritis was induced. Certain macaque species and cats are now known to be naturally infected with H. pylori, and these animals are susceptible to experimentally induced infection with the organism as well. Interestingly, as the ability to manipulate and grow H. pylori in vitro increased, so did the ability to colonize it in animal models. Helicobacter pylori has now experimentally induced gastritis in germfree euthymic and nude mice and in conventionally housed mice. Six additional Helicobacter species have been isolated and identified from the stomachs of various mammals, including dogs, cats, ferrets, pigs, monkeys, and cheetahs; these organisms, similar to H. pylori, are associated with variable degrees of gastritis in their hosts. In addition to the discovery of gastric helicobacters, an increasing number of Helicobacter spp. have been isolated from the distal part of the gastrointestinal tracts of mammals and birds. Importantly, in one inbred strain of mice, A/JCr, persistent infection with H. hepaticus is linked to development of hepatic adenomas and adenocarcinomas. To date, the genus Helicobacter includes 17 named species as well as other formally unnamed closely related organisms. An overview of gastric helicobacters and naturally acquired Helicobacter spp.-induced disease in laboratory animals and, where appropriate, use of animal models to study H. pylori-associated gastric disease is presented. Similarities between Helicobacter infections and the epidemiology of the diseases induced by these bacteria in humans and animals also are highlighted.