What is the definition of an infectious disease?

An infectious disease is defined as a disease caused by pathogens that can spread from one individual to another. Pathogens include microorganisms such as bacteria, viruses, fungi, and parasites that can invade and multiply within the body, leading to illness. The ability to transmit these diseases is a critical characteristic, as it distinguishes infectious diseases from those caused by other factors, such as genetic conditions or environmental influences.

This definition encompasses a wide range of diseases that can be spread through various modes of transmission, including direct contact, airborne transmission, vectors (like mosquitoes), and contaminated surfaces. Understanding this definition is essential in the study of biology, as it highlights the importance of public health measures aimed at controlling outbreaks and preventing the spread of these types of diseases among populations.