7. Principles of Disease
Chapter 7

Terms of Disease
How to talk about diseases.

• Disease – any negative change in a person’s health – to reduce the fitness of the host. • Etiology – The cause of the disease. • Microbial Flora – Microorganisms located on/in the body. • Normal Flora – Normal/natural microbial residents on/in the body. (Rarely cause disease if ever.)
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Health Science Microbiology David L. Beck, B.S., A.M., Ph.D.

Microbial Antagonism!!!!!
The normal flora protects against colonization by potentially pathogenic bacteria by: 1) Covering possible binding sites. 2) Competing for nutrients. 3) Affecting the pH and oxygen concentration. 4) Producing antimicrobial compounds that inhibit the growth of other microorganisms. Normal flora - Microorganisms that infect the body without causing disease. Some establish a permanent relationship with the body and some are present for limited periods of time. In utero, the mammalian fetus is in a sterile solution (amniotic fluid). The normal flora begin to be introduced when the baby passes through the birth canal. Additional organisms enter when breathing begins and feeding starts. Within the first 2 or 3 days of life, most of the normal flora have appeared - the remaining microorganisms are added during the next few weeks of life.
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Reminder

Continuum of Infection/Disease
Low Symptoms Mutualism Small Benefit Small Harm Mild Disease High Death

Normal Host
Disease Potential Low Normal Flora Opportunistic Infection (True) Pathogen
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High ??Normal?? Flora

Robert Koch Koch’s Postulates
It is not normal flora – it causes disease!
1876 Robert Koch became the first person to isolate the causative agent of an infectious disease and prove that it was the causative agent. Working out of a closet in his home he isolated Bacillus anthracis from an anthrax infected patient and then inoculated that organism into mice and showed that it caused anthrax in the mice.
Study Hint: Associate Isolate Inoculate Reisolate

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Course of the Disease

1. 2. 3. 4. 5.
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Incubation Period – the time for the pathogen to enter the body and begin growing. No symptoms are noted. Prodromal Period – First mild symptoms appear. Often not noted, or vague in nature. Period of Illness – “Major” symptoms are noticed. Period of Decline - Symptoms are there but are decreasing. Period of Convalescence – When “major” symptoms are gone. The patient is “fine”. But has not finished healing – has not returned to a preinfection state.

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Incubation Period
Time Before Onset of Prodrome

Contagious Period of transmission of the Disease
Different pathogens are contagious at different times.

FYI
A C
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B

D

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Course of the Disease

HIV – a double peak

Viral Load
Note – Some diseases present with two periods of illness. Representing an initial infection, and then a systemic infection.

Flu Symptoms Convalescence

Death

Note that recovery may or may not be complete. Loss of symptoms does not always equal loss of pathogens. Latent and chronic infections can continue for decades. Chronic infections can become severe again later in life.

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3 – 10 years (without suppression)

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Herpes – A latent infection
• An initial infection is more severe usually followed by small “flare-ups”

Disease Terms
• • • • • • Infection – Occurrence of a microorganism in/on the host. May or may not be associated with disease. Acute Disease – Disease symptoms are high. Chronic Disease – Infection Is long term with mild to severe infections. Insidious – Hard to detect or notice. May increase slowly with time. Latent – The disease becomes dormant in the body and may re-emerge at a later time. Usually used for viral infections. Persistent – Ongoing infection, often with little overt (obvious) disease. Usually used for bacterial infections.

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FYI Persistent bacterial infections
Some examples

Granuloma
Containment of persistent