Which term describes an infection that occurs when the body's normal defenses are not functioning properly?

The term "opportunistic infection" refers to infections that occur when the body's natural defenses, such as the immune system, are compromised or not functioning properly. This allows normally non-harmful microbes, which may reside in or on the body without causing any issues, to take advantage of the weakened state and lead to infections.

Opportunistic infections are particularly common in individuals with weakened immune systems, such as those with HIV, cancer patients undergoing chemotherapy, or anyone on immunosuppressive therapy. The concept highlights the importance of a healthy immune response in preventing infections that would not typically affect a healthy individual.

In contrast to other options, terms like "mutant infection," "nonpathogenic infection," and "recessive infection" do not accurately convey the situation described. "Mutant" typically refers to altered strains of pathogens, not specifically about the body's defenses. "Nonpathogenic" indicates organisms that do not cause disease, and "recessive" describes genetic traits rather than infectious diseases. Thus, the correct understanding lies in recognizing how compromised immunity leads to these opportunistic threats.