The Infection Model Quiz

See Pathogen. Option A is correct because the pathogen is the microorganism that causes the infection. In the basic infection model, a healthy person (the patient) meets a pathogen, becomes infected and then moves along a pathway to treatment and an outcome. The pathogen can be a virus, a bacterium, a fungus or a parasite. The model is useful because it separates the parts of an infection into clear steps: the agent that causes the infection (the pathogen), the person who is infected, how the organism spreads, how the infection is treated and prevented, and how the patient does in the end. A pathogen is the starting point of this pathway, so identifying it is the first step in understanding the infection and in choosing treatment. It also helps to keep apart words that sound similar. Pathogenesis is the process of disease, not the organism itself, while a commensal is a normal resident of the body that usually causes no harm. Memory aid: the pathogen is the cause of the infection, while pathogenesis is how the disease arises.

• Pathogen: the microorganism that causes the infection.
• Types: a virus, bacterium, fungus or parasite.
• Not the same: pathogenesis is the process of disease and a commensal is a harmless normal resident.