What is the definition of an illness that occurs through the transmission of an infectious agent?

A communicable disease is defined as an illness that is transmitted from one individual to another through the spread of an infectious agent. This transmission can occur through various means such as direct contact, airborne particles, or contaminated surfaces, among others. The key characteristic of a communicable disease is its ability to spread from person to person, often requiring specific conditions for the infectious agent to propagate.

In contrast, chronic diseases typically refer to long-lasting conditions that may not necessarily result from infectious agents and often have non-infectious causes such as lifestyle factors or genetic predispositions. Contagious diseases are often used interchangeably with communicable diseases, but they specifically imply a higher probability of spread, typically through direct contact. Genetic diseases arise from alterations in DNA and do not involve transmission through infectious agents. Understanding the precise definitions helps differentiate between various types of diseases and highlights the importance of controlling the spread of communicable diseases within communities.