Transcript Mechanisms of Pathogenicity

Define a Few Words:
 Pathogen
 Pathology
 Pathologist
 Pathogenicity
 Pathogenesis
4 Phases of an Infectious Disease
 1. Incubation Period

Time that elapses between the arrival of the
pathogen and the onset of symptoms.
 2. Prodromal Period

Stage in which symptoms are not experienced but
patient typically feels like they are “coming down
with something.”
 3. Period of Illness

The time during which symptoms of a particular
disease are present.
 4. Convalescent Period

The time in which patient recovers.
Location of Infections
 Localized Infection

Infection stays in one area
 Systemic Infection

Infection spreads throughout body
Disease Description
 Acute Disease


Has a rapid onset, usually followed by relatively
rapid recovery.
Ex. influenza
 Subacute Disease


Intermediate between acute and chronic diseases.
Onset more rapid than a chronic disease but less
suddenly than most acute diseases.
 Chronic Disease


Slow onset and lasts a long time.
Ex. Tuberculosis, syphilis
Symptoms Versus
Signs of a Disease
 Symptom of a Disease

A subjective indication that a person is
experiencing a disease.
 Symptomatic Disease

Experience symptoms.
 Asymptomatic Disease

Do not experience symptoms.
 Signs of a Disease

An objective sign of a disease.
Latent Infections
 An asymptomatic infection capable of
manifesting symptoms under particular
circumstances or if activated.
 Ex. Chicken Pox –
 Shingles
www.nlm.nih.gov
Primary vs. Secondary Infections
 Primary infections
 First disease that results in another disease (secondary
infection)
 Secondary infections
 The result of a primary infection
Steps in the Pathogenesis
of Infectious Diseases
 1. Entry
 2. Attachment
 3. Multiplication
 4. Invasion
 5. Evasion of Host Defenses
 6. Damage to Host Tissue
Virulence
 Can use this word in 2 ways:
 1. Can say that a microorganism is virulent or
avirulent.

Ex. Different strains of Corynebacterium
diphtheriae (strains that produce diphtheria).
 Can say that one pathogen is more virulent
than another pathogen.

Ex. Different strains of Streptococcus pyogenes.
Virulence Factors
 Characteristics that allow a pathogen to
attach, escape destruction, and cause
disease.
 Receptors


Attachment
Molecule on host cell that are recognized by the
pathogen.
Pathogen binds to host cell receptor.
 Adhesins

Molecule on pathogen that recognizes and binds to
the host cell receptor.
 Bacterial Pili

Long, thin, hair-like, flexible projections on
pathogen (composed mostly of proteins) that allows
it to bind to host cell.
Obligate Intracellular Pathogens
 Pathogens must live within host cells to
survive and multiply.
 Ex. Rickettsias infect endothelial cells and
vascular smooth muscle cells.
www.cals.ncsu.edu
www.microbelibrary.org
Facultative Intracellular Pathogens
 Capable of surviving in an intracellular and
extracellular environment.
 Mechanisms of survival
 Ex. Mycobacterium tuberculosis
www.sunysb.edu
Capsules
 Encapsulated bacteria are often harder to
engulf by phagocytic white blood cells
because they lack surface receptors.
 Phagocytes have difficulty engulfing this
bacteria.
www.cbc.ca
Flagella
 Allow motile bacteria to infect areas that
nonmotile bacteria cannot reach.
 May be able for bacteria to avoid
phagocytosis.
biology.clc.uc.edu
Exoenzymes
 Major mechanism by which pathogens
cause disease.
 They are produced by a pathogen.
 Enables pathogen to evade host defense
mechanisms, invade, or cause damage to
body tissues.
Exoenzymes
 Necrotizing Enzymes
 Coagulase
 Kinases
 Hyaluronidase
 Collagenase
 Hemolysin
 Lecithinase
Toxins
 Poisonous substances that are produced by a
microorganism that often cause disease.
 2 categories of toxins:
 1. endotoxins
 Part of cell wall of gram-negative bacteria that
can cause problems.
 2. exotoxins
 Toxins produced within cells and then released
from the cells.
Endotoxins
 Ex. Septicemia caused by gram-negative
bacteria.
 Caused by the lipid portion of its cell wall
which is the endotoxin.
 Causes chills, fever, extreme exhaustion, and
possibly septic shock.
Exotoxin
 Poisonous proteins produced by pathogens.
 Often named for their target organs.
 Ex. Neurotoxins


Affect the central nervous system.
Ex. Clostridium tetani
 Ex. Enterotoxins



Toxins that affect the gastrointestinal tract.
Often cause diarrhea and vomiting.
Ex. Salmonella spp.