In epidemiology, what would you call a person or animal that carries and transmits a pathogen without showing symptoms?

The term used to describe a person or animal that carries and transmits a pathogen without exhibiting any symptoms is "carrier." Carriers may harbor infectious agents and can spread them to others, even though they themselves do not show any signs of illness. This asymptomatic state makes them particularly important in the study of epidemiology, as they can contribute to the spread of infectious diseases, complicating control efforts.

In contrast, a "host" refers to an organism that supports the growth and development of a pathogen, but this term does not specifically imply the absence of symptoms. A "vector" refers to an organism, often an insect, that transmits a pathogen from one host to another, but is not itself a carrier in the sense of harboring the pathogen without showing symptoms. Lastly, "reservoir" pertains to the environment or organism in which a pathogen lives and multiplies, serving as a source for infection, but it does not indicate the individual is asymptomatic. Thus, the correct answer emphasizes the unique role of carriers in disease transmission within the field of epidemiology.