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Essentials of Pathophysiology
CHAPTER 14
MECHANISMS OF INFECTIOUS
DISEASE
PRE LECTURE QUIZ (TRUE/FALSE)
Creutzfeldt-Jakob disease and mad cow disease
are examples of prion-associated diseases.
F  Viruses are capable of replication outside of a
living cell.
T  The term portal of entry refers to the process by
which a pathogen enters the body.
F  Some fungi are members of normal human
microflora.
F  All organisms cause infectious illness in
humans.
T 
PRE LECTURE QUIZ
Acute

Infections that develop in patients while they are
hospitalized are called _________________.
–itis

Adding the suffix ______________ to the name of the
involved tissue usually designates inflammation of an
anatomic location.

The _________________ stage in the disease course
is the period during which the host experiences the
maximum impact of the infectious process.

____________________ refers to the collection of
signs and symptoms expressed by the host during the
disease course

Ticks, mosquitos, mites, and lice are examples of
___________________, a type of organism that
derives benefits from its biologic relationship with
another organism.
Nosocomial
Parasites
Symptomatology
INFECTION OR COLONIZATION WITH
MICROORGANISMS

“Infection” or “colonization” means that
microorganisms are multiplying in or on the
host
Discussion:
 Do you have any infections or colonizations
at this moment? List as many as you can
identify
 Are they normal, or are they making you ill?
INFECTION OR COLONIZATION WITH
MICROORGANISMS (CONT.)




Over 300 different species of bacteria live in the large
intestine
Bacteria and fungi live on our skin
The mouth and pharynx contain many species of bacteria
The vagina contains acid-producing bacteria
MICROFLORA






The microorganisms normally living in or on your body
Some are useful
Many have no effect
Pathogens cause disease
All are capable of causing disease if your health and
immunity are weakened
Opportunistic pathogens
QUESTION
True or False.
All interactions between humans and
microorganisms are detrimental.
ANSWER
False
Rationale: Some microorganisms perform
important functions for their human hosts, like
producing vitamins, assisting digestion, or
preventing harmful pathogens from entering
the host.
KINDS OF INFECTIOUS AGENTS

Prions
 Small
modified infectious host proteins
 Abnormally shaped versions of your own proteins
 Cause normal proteins to change their shape
and become new prions
 Can clump together and damage cells
 Cause degenerative disease in the central
nervous system (e.g., mad cow disease)
KINDS OF INFECTIOUS AGENTS (CONT.)

Viruses
 Protein coat
surrounding nucleic
acid core
 Have no metabolic
enzymes of their own
 Insert their genome
into a host cell’s DNA
 Use that cell’s
metabolic machinery to
make new viruses
KINDS OF INFECTIOUS AGENTS (CONT.)

Bacteria



Cells without membranebound organelles
(prokaryotes)
Can live independently
Use infected organism for
food and shelter
KINDS OF INFECTIOUS AGENTS (CONT.)

Bacteria
 Can produce toxins
 Exotoxins are proteins
released by bacteria
 They damage or kill
host cells
 Endotoxins are parts
of the bacterial cell
wall
 They cause host
immune reactions
KINDS OF INFECTIOUS AGENTS (CONT.)

Mycoplasmas, rickettsiae, chlamydiae
 Smaller than bacteria
 Mycoplasmas lack cell walls
 Rickettsiae and chlamydiae have to live inside
cells to metabolize, like viruses
KINDS OF INFECTIOUS AGENTS (CONT.)

Fungi
 Most require a cooler
temperature than
human core body
temperature
 So most infections
are on the surface of
the body
Tinea is a fungal
infection of the
skin
KINDS OF INFECTIOUS AGENTS (CONT.)

Parasites



Protozoa: malaria,
amoebic dysentery,
giardiasis
Helminths:
roundworms,
tapeworms, flukes
Arthropods: ticks,
mosquitoes, mites,
lice, fleas
KINDS OF INFECTIOUS AGENTS (CONT.)

Parasites



Protozoa: malaria,
amoebic dysentery,
giardia lamblia
giardiasis
Helminths:
roundworms,
tapeworms, flukes
Arthropods: ticks,
mosquitoes, mites,
lice, fleas
Trichomonas vaginalis
QUESTION
Which pathogen is an intracellular parasite
consisting of a protein coat surrounding a
nucleic acid?
a. Prion
b. Virus
c. Bacteria
d. Protozoa
ANSWER
Virus
Viruses have no organized cellular structure like
bacteria and protozoa. Viruses can only
replicate inside another cell; prions cannot
reproduce at all.
b.
DISCUSSION:

How many ways could you have become infected
today? How could you have experienced:
 Direct contact with a pathogen?
 Ingestion of a pathogen?
 Inhalation of a pathogen?
 Contact with a zoonosis?
 Contact with a nosocomial infection?
 Contact with a fomite?
SYMPTOMATOLOGY
infection
-Collection of signs and symptoms
expressed by the host during the
disease course.
Also known as the clinical picture or
disease presentation
inflammatory and
immune
responses attack
infective agent
SPECIFIC: signs
and symptoms of
local damage and
inflammation
NONSPECIFIC:
signs and
symptoms of
systemic
inflammation
SCENARIO:
A 5-year-old boy has an ear infection…

He complains of pain in his ear and cannot hear on that side.

When you look into his ear, you see a red, bulging eardrum with pus
behind it.

He has a fever, sweats, and complains of joint aches.

Blood tests show an elevated white blood cell count.
Question:

Use the model of symptomatology to classify these signs and
symptoms.
DISCUSSION
What stage of an infection are you in?
 How many people in the class are in:
 The incubation stage?
Pathogen begins replication w/o
recognizable symptoms
 The prodromal stage?
Initial appearance of mild vague
symptoms
 The acute stage?
Host experiences maximum
impact of the infection
 The convalescent stage?
Containment of infection,
progressive elimination of
 The resolution stage?
pathogen
Total elimination of pathogen
How can you tell?
and signs
TERMS FOR INFECTION AND DAMAGE

-itis means
 May
inflammation
or may not be due to infection

-emia means in the blood

Sepsis or septicemia means
bacterial toxins in the blood
VIRULENCE FACTORS

Make an infection more likely to cause disease

Toxins: exotoxins and endotoxins

Adhesion factors help infective organism stick to the
body

Evasive factors help keep immune system from
killing infective agent
QUESTION
True or False:
Certain bacterial cells release proteins called
endotoxins during growth.
?
ANSWER
False
Exotoxins are proteins; endotoxins contain no
protein (they are composed of lipids and
polysaccharides). Endotoxins are not released
during bacterial cell growth.
SCENARIO:
A woman’s stomach contained the bacterium
Helicobacter pylori…

For many years, the woman was healthy

Then she took on a new stressful job, moved,
and began to care for her elderly parents

A few months later, she began to suffer
stomach pains and vomited blood

She was diagnosed with a bleeding ulcer
SCENARIO (CONT.)
Question:
 How does each of these terms relate to her case?
 Portal of entry
 Site-specific pathogen
 Opportunistic pathogen
 Evasive factors
 Invasive factors
SEROLOGY
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

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After exposure to an
infectious agent, the
body produces
antibodies
Antibody titer rises
IgM: rises during the
acute phase, then
falls
IgG: remains elevated
after the acute phase
SCENARIO
A month-old baby is ill:

Serum analysis shows that she has IgG against HIV and
IgM against Pneumocystis
Does not cross placenta
Question:
 What inferences can you make?
Crosses placenta
Caused by protozoan that
infects immunocompromised
people
ANTIBACTERIAL AND ANTIVIRAL DRUGS
•
We have more drugs to kill bacteria than to kill
viruses, and more drugs to kill viruses than to
eradicate prions
Question:
•
Why has it been easier to develop antibacterial
drugs than antiviral drugs?
•
Why not use antibacterial or antiviral drugs to
destroy prions?
ANTIBIOTICS KILL BACTERIA BY TARGETING:
Look for something different in bacteria from eukaryotes
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Cell wall synthesis Peptidoglycan
Ribosomal differences
Protein synthesis
Nucleic acid synthesis DNA sequence, polymerase, r. transcriptase
Bacterial metabolism Folic acid synthesis
Bacteria Fight Back By:
• Inactivating antibiotics
• Changing antibiotic binding sites
• Using different metabolic pathways
• Changing their walls to keep antibiotics out
ANTIVIRAL AGENTS KILL VIRUSES BY:
Made as one long chain of
AAs then cut with proteases



Blocking viral binding
to cells
Blocking viral RNA or
DNA synthesis
Blocking production
of the protein coats
(capsids) of new
viruses
Must have for
replication
Contains attachment
proteins
QUESTION
What type of infections are treated based upon
the results of a Gram stain?
a. Fungal
b. Viral
c. Bacterial
d. Parasitic
ANSWER
Bacterial
Bacteria are commonly classified according to
Gram stain. Gram-positive and gram-negative
organisms are treated with specific antibiotics
that target that type of infection. For example,
penicillin targets gram-positive organisms.
If the cause of bacterial infection is unknown,
broad-spectrum antibiotics may be prescribed,
targeting both gram-positive and gram-negative
organisms.
c.