What is the definition of a communicable disease?

A communicable disease is defined as a disease caused by an infectious agent that can be transmitted from one individual to another. This definition includes diseases that are caused by pathogens such as bacteria, viruses, fungi, or parasites. Understanding this definition is crucial in the context of public health, as it highlights the need for preventive measures like vaccinations and good hygiene practices to control the spread of these diseases.

In contrast, the other definitions do not adequately describe communicable diseases. A disease that cannot be transmitted does not fall into this category at all, while diseases that solely affect animals would be classified as zoonoses if they can be transmitted to humans. Lastly, defining a communicable disease as always chronic is misleading, as many communicable diseases can be acute and resolve within a short period of time. Thus, option B correctly encapsulates the essence of what a communicable disease is.