The epidemiology of Helicobacter pylori continues to be an area of discovery and controversy in the 21st century. The transmission of this bacterium from mother to child allows Helicobacter DNA to mimic the evolution of maternal mitochondria DNA. But as Helicobacter carry many more genes than mitochondria, bacterial taxonomic studies can resolve human migrations over the past 50,000 years. Similarly, transmission of Helicobacter from man to animal is also possible, with interesting implications.
It is likely that nearly the whole human race was infected by the early 20th century, suggesting that Helicobacter was both an extremely well adapted pathogen and possibly, a beneficial symbiont. Speculation about a beneficial role for Helicobacter has even arisen. It may protect from asthma and, by increasing acid secretion, it could protect from more dangerous gastrointestinal infections. But in the 20th Century, improved nutrition caused acid secretion to be high enough to sustain chronic peptic ulcer. Additionally, humans lived long enough to develop gastric cancer, a disease caused by lifelong mucosal inflammation. Luckily, modern therapies have efficiently dealt with the ubiquitous gastric pathogen and proton pump blockers have enabled us to mop up any excess acid which might damage the oesophagus.
Whereas eradication of Helicobacter is easily achieved in Western countries, prevention of new helicobacter infections would achieve the same goal. Detection of H.pylori in the environment is difficult so its transmission is not well understood. In developed countries the infection must arise from other infected family members, especially mothers and perhaps grandmothers. Pre-mastication of food, licking and sucking of pacifiers and excessive oral contact which might lead to saliva transfer, are implicated. In developing countries, prevalence in young children is an index of water quality and general hygiene. However, if families cannot avoid faecal contamination, or governments cannot provide the population with a clean water supply, then Helicobacter infection will remain as a useful index of a population’s socioeconomic status.