What is a person or animal that harbors a specific infectious agent without discernible clinical disease who serves as a potential source of infection?

• A. Carrier
• B. Reservoir
• C. Vector
• D. Host

Answer: (A)

Asymptomatic carriage is when an individual harbors an infectious agent and can transmit it to others even though they show no symptoms. This state is what we call a carrier. Carriers can spread disease during the incubation period, after apparent recovery, or persistently in a chronic form, sustaining transmission in a population without appearing ill themselves. This concept matters for control because you can have ongoing infection chains fueled by people who look healthy.

This differs from a reservoir, which is the natural habitat or source where the pathogen lives and persists, which could be an environment, an animal, or a group of people, not necessarily someone actively contagious. A vector is a living intermediary that transfers the pathogen from one host to another, like a mosquito transmitting a parasite or virus. A host is any organism capable of being infected, regardless of whether they show symptoms; a host can be ill or asymptomatic, but the term doesn’t specifically imply contagious carriage.