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Table 2 H. pylori reservoirs.

From: Helicobacter pylori: a poor man's gut pathogen?

Hypothesis Evidence/Example studies Ref.
Food   
   - Contaminated food prepared under unhygienic conditions is a probable mechanism for transmission. A positive correlation was reported between prevalence of infection and consumption of food from street vendors in Peru. [70]
   - The daily amount of raw vegetables is a risk factor, which possibly implies a role for water too. In the Colombian Andes, frequent consumption of raw vegetables was associated with likelihood of infection. [99]
   - Sheep and cow milk can be vehicles for transmission. See below (under Animals) [118, 119]
Animals   
   - Several animal species were suggested as H. pylori reservoirs. H. pylori was isolated from:  
  - pigtailed monkeys [120]
  - rhesus monkeys [121]
  - cats [122]
  - sheep [123]
  - cockroaches [124]
  - houseflies (but the housefly hypothesis was challenged) [125, 126]
   - Working with animals may increase risk, and animal-to-human transmission is possible. H. pylori was suggested as zoonotic, occupational infection to meat and abattoir workers. [127, 128]
  In Colombian Andes, children who had contact with sheep had higher prevalence odds. [99]
  Dore et al. stated that animals, especially sheep and dogs, could transmit H. pylori to humans (shepherds) in Sardinia. [129]
   - H. pylori can be recovered from animal products. H. pylori was recovered from sheep and cow milk. [118, 119]
   - Experimental animal colonization is possible. Bacillary forms of H. pylori were used to colonize germ-free piglets. [130]
Water   
   - Water contamination is a risk factor for H. pylori infection. Many reports, mostly from developing countries, suggested contaminated water sources as risk factors. Examples include studies performed in Peru, Chile, and Kazakhstan. [105, 131, 132]
   - Water from running, municipal, and underground sources, as well as wastewater has been suggested as reservoir for H. pylori. - Municipal water [105]
  - Well water [133]
  - Running water [99, 134]
  - Wastewater [135]
  - H. pylori even survives in chlorinated water. [136]
   - H. pylori proteins and DNA can be detected in water. - by immunological methods [137]
  - by PCR [133, 138]
  - by hybridization methods [139]
   - Viable H. pylori can be detected and isolated from water. - as individual cells [140]
  - associated with biofilm [141, 142]
  - cultured [135]
  1. Examples of studies on different environmental sources of H. pylori and their role in H. pylori transmission.