Table 2.
H. pylori reservoirs.
| 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] | |
Examples of studies on different environmental sources of H. pylori and their role in H. pylori transmission.