The Infection Cycle
Infection occurs when an organism enters the body and starts to grow. Dis-ease only occurs if the organism starts to multiply and produce symptoms. Our bodies have tremendous capacity to fight off organisms. When the protective mechanisms fail or are compromised, dis-eases occur.
The most dangerous organisms are those that are virulent and contagious. Organisms must enter the body to cause disease. The organism must adhere to a specific cell, invade, colonize and inflict some type of damage to the host. This chain of events is the same for all organisms:
Entrance
Entrance to the host occurs through the normal openings like the nose, eyes, anus, genitalia, or open wounds. Some organisms can grow at the initial site of entry, many invade and start to grow in different organs where they are hard to detect.
Some organisms grow within the host cells. Others grow in blood. Micro organisms can cause tissue damage by releasing a variety of toxins or destructive enzymes.
Infectious agent
The organism must be able to grow, multiply, be able to enter the body and have the ability to cause disease. Infectious agents which cause disease in humans include bacteria, fungi, viruses, and parasites like the toxoplasma gondii:
Reservoir
Reservoir is a place where organisms can thrive and multiply, like inside the human body or outside, like in an inanimate environment, such as water, AC units, furniture, or in a tick.
The reservoir for a disease is the site where the infectious agent survives. Beside insects, animals also serve as reservoirs for infectious organisms.
