In disease transmission, what is a vector?

• A. A non-living carrier
• B. A living organism that transmits an infectious agent from an infected animal to a human or another animal
• C. A nutrient for pathogens
• D. A climate factor that promotes disease

Answer: (B)

The main idea here is how diseases move between hosts through living carriers called vectors. A vector is a living organism that transmits an infectious agent from an infected animal to a human or another animal. Think of a mosquito spreading malaria or dengue, or a tick spreading Lyme disease—the pathogen uses the vector to get from one host to another. Sometimes the pathogen multiplies inside the vector, which is typical for biological transmission, but even when the vector only carries the pathogen on its body (mechanical transmission), the carrier remains a living organism and functions as a vector.

Other descriptions describe non-living carriers, nutrients, or climate factors rather than a living transporter, so they don’t fit the concept of a vector.