What characterizes an infectious disease?

An infectious disease is characterized by the presence of biological agents such as bacteria, viruses, fungi, or parasites that invade the body and cause illness. The key aspect of option B is that it encompasses any condition that leads to bodily dysfunction resulting from a living agent. This includes a wide range of diseases caused by various pathogens, highlighting the biological nature of infectious diseases and their ability to disrupt normal physiological functions.

Infectious diseases can manifest through direct invasion of tissues, toxin production, or immune response triggers. This broad definition is essential for understanding the range of infectious agents and processes involved in such diseases. The other options do not adequately capture the essence of infectious diseases; they either restrict the causative factors to specific types like viruses or toxins, or they refer to non-infectious causes such as genetic mutations. Thus, option B effectively encapsulates what characterizes an infectious disease, making it the correct choice.