A vector is defined as:

A vector is defined as:

• A. The way a pathogen moves from its reservoir to host with a living vessel.
• B. A nonliving carrier of pathogens.
• C. An immune cell that blocks infection.
• D. A disinfectant.

Answer: (A)

The main idea is that a vector is a living organism that transmits a pathogen from its reservoir to a susceptible host. A vector is alive and often the pathogen develops or multiplies within it before transmission, which is why it can effectively move the pathogen between people or animals. Classic examples include mosquitoes spreading malaria or dengue, and ticks transmitting Borrelia to humans. Some vectors are biological, meaning the pathogen changes inside the vector, while others are mechanical and simply carry the pathogen on their bodies without internal development. The other descriptions refer to a nonliving carrier (a fomite), an immune cell that blocks infection, or a disinfectant, none of which are vectors.

The main idea is that a vector is a living organism that transmits a pathogen from its reservoir to a susceptible host. A vector is alive and often the pathogen develops or multiplies within it before transmission, which is why it can effectively move the pathogen between people or animals. Classic examples include mosquitoes spreading malaria or dengue, and ticks transmitting Borrelia to humans. Some vectors are biological, meaning the pathogen changes inside the vector, while others are mechanical and simply carry the pathogen on their bodies without internal development. The other descriptions refer to a nonliving carrier (a fomite), an immune cell that blocks infection, or a disinfectant, none of which are vectors.