Cholera is a deadly disease that is present in many third world countries, including Bangladesh and India. The disease has been infecting people for thousands of years, meaning it is more likely to be causing evolutionary changes in humans, compared to newly emerged diseases.
Sure enough, researchers from Massachusetts and Bangladesh have found that the human genome has evolved in people who are more likely to contract cholera. Regina LaRocque, an infectious disease specialist from Massachusetts General Hospital and Elinor Karisson, a computational geneticist from Harvard, along with collaborators in Bangladesh, have determined that 305 regions of the human genome were altered by natural selection in individuals in Bangladesh. DNA from 36 Bangladeshi families was compared to that of people from northwestern Europe, West Africa, and eastern Asia. The researchers utilized a new statistical technique that finds regions of the genome that are being affected by natural selection.
But how can we be sure that cholera is the driving force of the genome alterations found in these Bangladeshi families? One piece of evidence is that a category of genes that appear to be evolving due to cholera include those that code for potassium channels and their release of chloride ions into the intestines. This seems reasonable because cholera bacteria induce these potassium channels to release chloride ions, which leads to diarrhea, a prevalent symptom of cholera. Additionally, other genes that are affected by cholera include those that regulate the protein NF-kB, which is a major player in inflammation, also a symptom of cholera. A final piece of evidence supporting the phenomenon that DNA is evolving in response to cholera is that inflammasome, a protein complex inside human cells that can detect pathogens and initiate an inflammatory response.
Overall, the evidence that the human genome is adapting in response to cholera is an intriguing finding and could help scientists make more effective vaccines against the disease.