A causative agent is any microorganism that is capable of producing an illness. These include bacteria, virus, parasites, fungi protozoa and other harmful microorganism.., This includes the environment and objects which an organism can thrive in and multiply.
 This is the path or way in which a certain organism leaves the reservoir.
 This is the means by which a certain infectious agent passes from the portal of exit from the reservoir to the susceptible host. It can be transmitted through four modes:


Contact Transmission – the most common mode of transmission which is divided into:

Direct contact – the infection is transferred from person to person.
Indirect contact – the infection is transferred when a person comes in contact with a contaminated object.


Droplet spread – the infection is transferred through respiratory secretions that can travel up to 3 feet (0.9 m).
Airborne transmission – the infection is transferred through fine particles that are suspended in the air for a prolonged period and inhaled.
Vehicular transmission – the infection is transferred through articles or substances that harbour the organism until it is ingested by the host; transmission by inanimate objects such as food, water, fomites or dust.
Vector-borne transmission – the infection is transferred by intermediate carriers such as mosquitoes, flea, flies and other bites from animals or insects.
 This is the venue wherein the microorganism gains complete entrance into the host.
 This includes a weakened human body or animals; in cases where their immune system cannot fight the microorganism, the microorganism will launch an infectious disease.
 That is, altering the mode of transmission. If the person knows how to prevent it, then the likelihood of getting a communicable disease is lower.
Understand that there must be a causative agent .
Know that there must be a reservoir of infection.
Be aware that there must be a portal of exit.
Recognize the different modes of transmission.
Understand that there must be a portal of entry.
Be aware that the microorganism must have a susceptible host.
Know that avoiding communicable diseases is best done by breaking the chain of infection.
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