The person, animal, object or substance from which an infectious substance passes or is disseminated by host is called –
**Core Concept**
The question is testing the definition of a reservoir in the context of infectious diseases. A reservoir refers to the person, animal, object, or substance from which an infectious agent passes or is disseminated to a host.
**Why the Correct Answer is Right**
The correct answer is a reservoir because it harbors the infectious agent, allowing it to multiply and potentially be transmitted to a susceptible host. This can occur through various routes, including direct contact, vector-borne transmission, or environmental contamination. The reservoir can be a living organism, such as an animal host, or an inanimate object, like a contaminated surface.
**Why Each Wrong Option is Incorrect**
**Option A:** A vector is an organism that transmits an infectious agent to a host, but it is not the source of the agent itself.
**Option B:** A host is an individual that harbors an infectious agent, but it is not the source of the agent.
**Option C:** A carrier is an individual that harbors an infectious agent but does not display symptoms, but it is not the source of the agent in the same way a reservoir is.
**Clinical Pearl / High-Yield Fact**
Remember that the reservoir is the source of the infectious agent, and it can be a living organism, an inanimate object, or even the environment itself.
**Correct Answer: D. Reservoir.