Besides the well established Helicobacter pylori reservoir, i.e. the human stomach, numerous other sources have been hypothesized. However, none has been definitely proven. In some instances (pig, sheep), Helicobacter species closely related but different from H. pylori were detected but the results were misleading because culture of sufficiently discriminating molecular techniques were not used. In other cases, the strain was really H. pylori (cat) but the case was anecdotal or the animal species (monkey) has so little contact with humans that the possible source has no epidemiological consequence. This is also the case for houseflies which theoretically can be a vehicle, but practically speaking are not because of too few viable bacteria present in faeces. Molecular epidemiology studies demonstrating the route of transmission (faecal-oral, oral-oral or gastro-oral) are still lacking but recent studies have confirmed the presence of viable H. pylori in vomitus and in faeces in the event of diarrhoea.