Data-dog's post about his possible ulcer reminded of an article I read today.
Helicobacter pylori a common pathogen that is found in the human gut, well known for producing some nasty ailments including ulcers can also cause stomach (gastric cancer) cancer. One God’s marvellous creations
What’s has been of interest to scientists for some time is that there is no correlation between the occurrence of gastric cancer and the percentage population infected with the H. pylori. This suggests that a combination of factors are responsible to facilitate a carcinogenic response.
A paper published yesterday provides evidence that one those other factors include the ancestry of both the human host and the pathogen. People that are infected with H. pylori strains that have a different ancestry from their own are more likely to suffer severe affects than people infected with a strain that co-evolved within their indigenous population.
The research involved the study of two Colombian populations the first being coastal population of primarily African ancestry and a population of largely Amerindian descent in the Andes Mountains. The first group exhibits a relatively low incidence of gastric cancer in comparison to the second group where the incidence is high.
In an attempt to understand this discrepancy in severity between the two populations a record of the strains of H. pylori afflicting patients from the two regions were kept. As patients requiring endoscopies came into the local they would donate a tissue sample. Bacteria within these samples were then cultured and analysed.
The researchers found that the H. pylori in the coastal region, with a low incidence of stomach cancer, were primarily of ancestral African makeup, just like their human hosts. Those in the second population where gastric cancer is more common, appeared to be more closely related to H. pylori of southern Europe, unlike the predominately Amerindian human population. The results suggested that a shared evolutionary history of humans and bacteria resulted in a less virulent host-pathogen relationship.
This would indicate that pathogens produce less virulent effects if they have co-evolved with their host. On the other hand if the host contracts a strain that has not co-evolved within its ancestry that person is more likely develop severe symptoms of infection.
The reason I found this fascinating is because this type of research is only possible because we understand the principles of evolution and common descent. The only reason that the research team looked at a correlation between the ancestry of pathogen and host was because the theory of evolution predicted it, another strand of evidence demonstrating how robust the theory is.