Final answer:
Fever is an important defense mechanism that enhances the immune response by increasing body temperature, affecting metabolism, and inhibiting pathogen activity, with endogenous pyrogens triggering the fever in response to infections such as viral ones.
Step-by-step explanation:
The importance of fever as a host defense mechanism can be summarized by understanding its role in enhancing the immune response, its causes which can include viral or bacterial infection, and its effect on the body which typically involves an increased metabolism. When a pathogen is destroyed by phagocytic leukocytes, endogenous pyrogens are released. These pyrogens travel to the hypothalamus, resetting the body's thermostat and inducing a fever. A heightened body temperature is beneficial as it conserves iron, a nutrient needed by bacteria, and increases the activity of the body's enzymes and protective cells while simultaneously inhibiting the activity of the pathogens. Additionally, the heat from the fever may directly kill the invading microorganisms.
In response to the original question, which asks about the importance of fever as a host defense mechanism, what causes fever, and how fever clears infection, the correct answer would be C) Enhances immune response, Viral infection, Increased metabolism. This answer reflects that fever is part of the immune system's response to infection, that a viral infection can cause fever, and that the metabolic rate is increased during a fever to facilitate clearing the infection.