Terminology

Host - An animal or plant that harbors or nourishes another organism.

Infection - Invasion by and multiplication of pathogenic microorganisms in a bodily part or tissue, which may produce subsequent tissue injury and progress to overt disease through a variety of cellular or toxic mechanisms.

Pathogen - Any microorganism capable of producing disease.

Reservoir - Person or animal that harbors pathogenic microorganisms but does not have the clinical disease. Serves as a source from which other individuals can be infected.

Flora - Microorganisms that live on or within a body to compete with disease-producing microorganisms and provide a natural immunity against certain infections. Flora are found on or in a healthy person.

Fomites (Fomes) - Nonliving articles, such as clothing, that can transmit microorganisms.

 

Exogenous mode of transmission is from outside the body.  

Examples: (1) a mosquito, tick or flea (2) a fomite, such as a cassette would be exogenous (3) West Nile virus would be exogenous.  

Endogenous mode of transmission from within one's own body.

Example: Normal flora (bacteria in the mouth)

 

Cycle of Infection

The cycle of infection is the factors that are involved in the spread of the disease. These factors are:

 

The Person Transmitting The Disease Has---

1. An infectious organism

2. A reservoir of infection

3. A portal of exit

 

The Person Contracting The Disease--

4. Is a susceptible host

5. Has a portal of entry

6. There is a means of transporting the organism from the reservoir to the susceptible individual

 

Establishment of An Infectious Disease

There are many factors involved in the establishment of an infectious disease. The process includes:

1. Encounter - The infectious organism comes into contact with the host.

2. Entry - An infectious microbe enters the body by either ingression or penetration.

3. Spread - The dissemination of the microbe through the body.

4. Multiplication - Most infectious agents must first multiply for the impact to be recognized.

5. Damage - There are innumerable ways in which an infectious agent can cause damage to a host. The damage can be either direct or indirect.

6. Outcome - There are three possible outcomes:

A. The host gains control of the infectious agent and eliminates it.

B. The infectious agent overcomes the host's immunities to cause disease.

C. The host and the infectious agent compromise and live in a somewhat anxious state of symbiosis.