What defines a communicable disease?

A communicable disease is specifically defined as one that can be transmitted from one individual to another or even from animals to humans. This characteristic of spreading is central to understanding how these diseases operate. For example, infections like influenza, tuberculosis, and certain viruses can move between individuals through various transmission pathways, such as respiratory droplets, direct contact, or vector-borne means.

Recognizing options that do not meet this definition helps to clarify why "C" is the correct choice. A disease that affects only animals would not be communicable to humans, thereby excluding it from the definition. Similarly, a non-infectious medical condition would not involve transmission at all, eliminating that choice as well. Lastly, conditions that are solely hereditary are passed down through genetics and do not involve transmission, further distinguishing them from communicable diseases. Thus, the ability of a communicable disease to spread between individuals or different species is what accurately defines it.