What term describes an individual with an active measles infection?

The term that best describes an individual with an active measles infection is "host." In the context of infectious diseases, a host is an organism that harbors a pathogen, which in this case is the virus responsible for measles. The host provides the necessary environment for the pathogen to live, reproduce, and cause disease.

While "carrier" is often used to refer to individuals who harbor a pathogen without exhibiting symptoms, this does not apply to someone with an active infection who is displaying symptoms of measles. A "reservoir" typically refers to a broader term that includes various habitats in which the pathogen can survive and multiply, including humans, animals, and environments. Lastly, "transmitter" usually refers to individuals or organisms that can spread the pathogen to others but does not necessarily imply that they are currently infected. Therefore, in the case of an individual with an active measles infection, "host" accurately captures their role in the context of the disease.