Is H Pylori an Environmental Threat?
If you set out to build a super-successful microorganism, how would you do it? First, you might ask what makes a microorganism successful. Most biologists would argue that a successful microorganism avoids being killed and therefore reproduces well and spreads widely. So, if your microorganism had an animal host, would it be better to maim and kill the host, or live quietly without causing trouble and thereby escape notice? Bacteria have caused many of humankind’s most dreaded illnesses (the plague, typhoid fever, cholera, botulism, and tetanus, to name a few). Although the names of these diseases might be household words, it could be argued that the bacteria that caused them are not particularly successful. Because they cause severe illness and/or death, they do not have an opportunity to spread widely before the host dies or becomes too ill to effectively pass the germ along. This is not the case with Helicobacter pylori.
The fact that H. pylori lives quietly inside the human stomach are what makes it such a successful organism. In most people there are no symptoms of infection, while in others the symptoms are mild. Only tiny percentage exhibit symptoms noticeable enough that the person seeks medical care, and this often occurs decades after the initial infection, leaving plenty of time to infect others along the way. Typically, the symptom that brings patients to the doctor is an intense, gnawing or burning pain in the stomach, which signals the formation of an ulcer. Ulcers were once thought to be caused by emotional stress and lifestyle (alcohol, smoking, etc.), but it is now recognized that the majority of them are the result of H. pylori infection. H. pylori infect over half the world’s population, but only about 10 percent of the population develops ulcers. This discrepancy has puzzled investigators for decades.
Why do only certain people exhibit symptoms of H. pylori infection? Is it some property of the individual, or something about the organism that makes the disease worse in some individuals than others? The answer is probably both. Individual differences in how the host’s immune system responds to infection combined with the nature of the infecting strain (i.e., what genes it carries) conspire to create greater damage in some people than in others. The diseases that H. pylori causes are thought to arise as a result of both direct damage by the bacterium and injury brought about by the host’s own immune system.
