Final answer:
The source of a disease can be within our body, such as opportunistic infections caused by normally harmless microbes, or it can be attributed to specific pathogenic strains, as seen with some E. coli strains that acquire virulence factors. It can also emerge from a geographic region's microorganisms or through contamination of food, water, and waste.
Step-by-step explanation:
The source of a disease can be found at various locations. Firstly, it can be within our body, such as when opportunistic infections occur from microbes that are normally harmless in one part of the body but cause disease if they end up in a different system. E. coli infections are good examples, where E. coli normally found in the large intestine can lead to urinary tract infections if it enters the bladder. Furthermore, diseases can also be sourced to our own microbes that reside in certain regions of our bodies or from all microorganisms in a certain geographic region.
Additionally, pathogenic E. coli strains can cause dangerous diarrheal diseases by acquiring virulence factors through horizontal gene transfer. This highlights the mechanism by which certain strains of E. coli can become a disease source.
Lastly, it is important to note that many pathogenic organisms are spread through contaminated food or water or by direct or indirect contact with human urine or faeces. It is essential to identify the correct source in efforts to prevent and control the spread of disease.