What characterizes an infectious disease?

An infectious disease is characterized by being caused by pathogens, which include bacteria, viruses, fungi, and parasites. These pathogens have the ability to invade a host organism and multiply, leading to disease. One of the defining aspects of infectious diseases is their transmissibility; they can spread from one individual to another or from the environment to a host, facilitating their spread through methods such as direct contact, airborne transmission, or vectors like insects.

The correctness of this choice stems from the understanding of how infectious agents operate within different environments and hosts. For instance, unlike non-infectious diseases, which can arise from genetic, environmental, or lifestyle factors, infectious diseases have a biological basis tied to these pathogens. Each of these pathogens has specific modes of transmission that determine how easily they can spread through populations, emphasizing the nature of these diseases.

While it's also relevant to note that not all infectious diseases lead to death, they vary widely in severity and outcomes based on the pathogen involved, the mode of transmission, and the host's health status. Thus, the choice indicating that infectious diseases are caused by pathogens that can be transmitted aligns with the fundamental definition and characteristics of infectious diseases.