What is a pathogen?

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Multiple Choice

What is a pathogen?

A pathogen is the disease-causing agent. It can be a virus, bacterium, fungus, protozoan, or even a prion—anything that directly leads to disease in a host. The key idea is that the pathogen is the cause of illness, not the organism that carries or hosts it. That’s why the correct choice describes an organism that causes disease. The other roles are about transmission or association with disease but do not define the agent itself: a vector transmits a pathogen between hosts, a host or reservoir can harbor vectors or pathogens without being the disease-causing agent, and a parasite is an organism that lives off another organism, which may or may not cause disease. For example, the influenza virus is a pathogen that causes flu; the mosquito is a vector that transmits that pathogen.

A pathogen is the disease-causing agent. It can be a virus, bacterium, fungus, protozoan, or even a prion—anything that directly leads to disease in a host. The key idea is that the pathogen is the cause of illness, not the organism that carries or hosts it.

That’s why the correct choice describes an organism that causes disease. The other roles are about transmission or association with disease but do not define the agent itself: a vector transmits a pathogen between hosts, a host or reservoir can harbor vectors or pathogens without being the disease-causing agent, and a parasite is an organism that lives off another organism, which may or may not cause disease. For example, the influenza virus is a pathogen that causes flu; the mosquito is a vector that transmits that pathogen.

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