Answer :
Final answer:
An infectious disease is caused by pathogenic organisms that can be transmitted between individuals, sometimes through vectors. These diseases are caused by bacteria, viruses, fungi, protozoa, and can be categorized based on their level of contagiousness. Despite medical advancements, they remain a leading cause of death globally.
Explanation:
A disease caused by pathogenic organisms that enter the body and which may or may not be spread from one person to another is known as an infectious disease. Infectious diseases can be caused by various types of pathogens, including bacteria, viruses, fungi, and protozoa.
These diseases can be spread through various mechanisms, such as direct contact with an infected individual or through a vector, an organism that carries pathogens from one host to another.
Infectious diseases can range from being highly contagious, like measles, to less so, like gonorrhea, depending on the mode of transmission of the pathogen.
Some infectious diseases have played significant roles historically, such as Typhoid Mary's case, which exemplifies how a single carrier can spread a disease without exhibiting symptoms themselves.
Despite advancements in medical research and treatments, infectious diseases remain a leading cause of death worldwide because they can spread rapidly, reproduce in the host, and cause damage to the host's tissues.