Pathogens are any type of bacteria, virus or fungi that causes disease in humans, according to Education Portal. These three types of organisms all have subspecies that may attack humans and cause them to become sick.
Pathogens are defined as microscopic agents in nature that can easily cause a person harm, states Education Portal. People come in contact with pathogens each day, but their immune systems work hard at all times to remove pathogenic bacteria, viruses and fungi from their bodies.
Viruses are small, infectious agents that are able to replicate inside of a living host. Without a living host a virus is unable to divide, replicate and thrive, according to Education Portal. Once a virus enters the human body it inserts itself into a cell and utilizes the cell's organelles and cellular machinery to copy itself and spread to other cells.
Bacteria is another pathogenic agent. Not every type of bacteria is pathogenic, and, in fact, the human body relies on commensal bacteria to complete essential mechanisms inside of the body, Education Portal states. Pathogenic bacteria can attack the human body and propagate throughout the body quickly to overpower the immune system and cause illness.
Fungi utilize every opportunity they get to attack humans, notes Education Portal. Yeast, mold and mushrooms are all fungi that may be pathogenic toward humans.