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Microbiology (PA 2205) > Pathogenicity, Spread, and Transmission of Infectious Diseases > Flashcards

Pathogenicity, Spread, and Transmission of Infectious Diseases Flashcards

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1
Q

Disease Triad - three components

A
  1. Host
  2. Environment
  3. Pathogen
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2
Q

Pathogenicity

A

The ability of an organism to cause disease

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3
Q

Definitions!
Virulence
Infectivity
Infectious Dose

A

Virulence: the ability to cause hot cell damage (degree of pathogenicity)
Infectivity: the ability to infect and colonize a host (infectivity is measured as infectious DOSE)
Infectious Dose: the minimum number of pathogens that will initiate an infection

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4
Q

There is an inverse relationship between ______ and ________

A

Infectious dose & virulence

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5
Q

Virulence

LD 50 vs ID 50

A

Can be estimated from experimental studies of determining:
50% Lethal Dose (LD 50) - the number of microorganisms needed to kill half of the hosts that are exposed to the pathogen
50% Infectious Dose (ID 50) - the number of microorganisms needed to cause infection in half of the exposed hosts

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6
Q

Virulence of an organism is determined by its ability to produce various ____ factors

A

Virulence factors

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7
Q

Attenuation

A

The decrease or loss of virulence

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8
Q

Virulence Factors:

  1. Adherence
  2. Evasiveness
  3. Invasiveness
  4. Production of Toxins
A
  1. Adherence: the attachment of the microorganism to body cells
  2. Evasiveness: ability to evade host defence mechanisms
  3. Invasiveness: ability to invade host tissues
  4. Production of Toxins: ability to produce/release substances that can cause tissue damage
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9
Q

Adhesive Mechanisms

A

Adhesion is the initial event in the pathogenesis of many infections when they attach to body cells
Attachment = a specific reaction b/w surface receptors & adhesive structures on the surface of microorganisms

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10
Q

Examples of Adhesive Mechanisms

A 
A) Fimbriae/Pili
B) Flagella
C) Capsule 
D) Spikes 
E) Exosomes by Parasites 
F) Pseudohyphae by Fungi
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11
Q

Invasiveness

A

The ability of organism to spread in a host tissue after establishing infection
Less invasive organisms = localized lesion
Highly invasive organisms - generalized infection

This is aided by the production of extracellular substances = invasins
-Most invasins are enzymes that act locally to damage host cells and/or have the immediate effect of facilitating the growth & spread of the pathogen

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12
Q

Toxigenicity

A

The ability of microorganisms to cause disease as determined by the toxin it produces which partly determines its virulence

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13
Q

EXOtoxins

ENDOtoxins

A

Exotoxins = a potent toxic substance formed and secreted by species of certain bacteria, outside body

Endotoxins = a complex bacterial toxin that is composed of protein, lipid, and LPS which is released only upon lysis of the cell (gram-negative bacteria dies)

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14
Q

Exotoxins

A

Action is enzymatic and has specific tissue affinity

Named according to what they do (ex. coagulase prevents phagocytosis by forming fibrin barrier around bacteria, fibrinolysin promotes the spread of infection by breaking down the fibrin barrier in tissues)

And according to where they act (cytotoxins)

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15
Q

Examples of Effects of Exotoxins

A
  1. Promotion of bacterial survival/spread
  2. Damage to host cell membrane
  3. Disruption of of cell metabolism
  4. Blockage of nerve-impulse transmission (neurotoxins)
    Example = Botulinum Toxin (decreases secretion of Ach)
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16
Q

Endotoxins

A

Endotoxins = lipid portion of LPS
Released when gram-negative bacteria die & their cell walls undergo lysis, thus liberating the endotoxin

Exert their effects by stimulating macrophages to release cytokines in very high concentrations

Biological activities causing:

  • Fever
  • Muscle proteolysis
  • Uncontrolled intravascular coagulation (DIC)
  • Shock
17
Q

Microbial Pathogenicity Damage to Host

Direct vs Indirect Damage

A

Direct Damage= tissue damage from disease process (toxins, enzymes)
Indirect Damage= tissue reactions from immunopathological response

18
Q

Ways in which BACTERIA cause tissue damage?

A

a. Inflammatory reactions d/t extra/intra cellular multiplication
b. Tissue changes/damage due to toxins
- -Endotoxins
- -Exotoxins

19
Q

Ways in which VIRUSES cause tissue damage?

A
  • Inhibit/alter host cell metabolism
  • Cause host cell lysis due to replication cycle
  • Cause host cell lysis due to immune action
  • Inflammatory reactions
  • Damage to immunocytes
  • Neoplastic change
20
Q

Ways in which FUNGI cause tissue damage?

A

Fungi are extracellular digesters
ENZYMES and metabolic by-products cause/contribute to tissue damage

  • -Zymosan is a ligand found on the surface of fungi, like yeast (endotoxin-like effects)
  • Dimorphism
21
Q

Ways in which PARASITES cause tissue damage?

A
  1. Mechanical obstruction
  2. Competition with host for resources
  3. Proteases: secretion of enzymes
  4. Immunological reactions
22
Q

Acute Disease
Subacute Disease
Chronic Disease

A

Acute= disease in which symptoms and signs develop rapidly and that runs its course quickly (LESS THAN 3 weeks)
Subacute - disease with time course & symptoms between acute & chronic (b/w 3-8 weeks)
Chronic= disease with usually mild symptoms that develop slowly and last a long time (MORE THAN 8 weeks)

23
Q

Latent Disease

A

Disease that appears a long time after infection

24
Q

Local Infection
Systemic Infection
Focal Infection

A 
Local = infection confined to a small region of the body 
Systemic = widespread infection of many systems
Focal = infection that serves as a source of pathogens for infections at other sites in the body
25
Q

Primary Infection

Secondary Infection

A

Primary - initial infection within a given patient

Secondary - infection that follow a primary infection; often by opportunistic pathogens

26
Q

6 Steps in the Chain of Infection

A
  1. Infectious Agent
  2. Reservoir
  3. Way out of the body
  4. Method of transmission
  5. Person at risk
  6. Way into the body
27
Q
  1. Infectious Agent
A

The germ AKA the micro-organism that can cause infection

Ex. bacteria, viruses, fungi & parasites

28
Q

Koch’s Postulates (4)

A
  1. The suspected causative agent must be absent from all healthy organisms, but present in all diseased organisms
  2. The causative agent must be isolated from the diseased organism and grown in pure culture
  3. The cultured agent must cause the same disease when inoculated into a healthy, susceptible organism
  4. The same causative agent must then be re-isolated from the inoculated, diseased organism
29
Q

Limitations to Koch’s Postulates (3)

A
  1. Pathogens can be isolated from patients who are NOT manifesting symptoms (asymptomatic carriers)
  2. Some pathogens that cannot be cultivated on existing media
  3. Exposures to pathogens do not always result in disease in all hosts
30
Q
  1. Reservoir
A

The place where micro-organisms can thrive & reproduce

31
Q

Nosocomial

Zoonotic Diseases

A

Nosocomial - acquired by patients while in health care facilities such as hospitals and clinics
Zoonotic Diseases - caused by infections that are shared between animals and people

32
Q
  1. Way Out of The Body
A

Portal of exit, how the micro-organism exits the reservoir

33
Q
  1. Methods of Transmission
A

Transmission = how a microorganism is moved from one site to another

34
Q

Modes of Disease Transmission

A

CONTACT
Direct - directly transferred from an infected person to another person
Indirect - microbes transferred through contaminated intermediate objects
VEHICLE
Airborne, Waterborne, Food Borne, Blood Borne
VECTOR
Mechanical (on insect bodies)
Biological (eg. lice, mites, mosquitos, tics)

35
Q

Horizontal vs. Vertical Transmission

A

Horizontal = transmission from one individual to another in the same generation
Vertical = transmission from an individual to its offspring
-During delivery, transplancental, in breastmilk

36
Q
  1. Person at Risk
A

Anyone, however, some people are particularly susceptible to infection

37
Q

Immunocological Status

A

Factors that affect the body’s natural ability to fight infection:

  1. Presence of underlying disease
  2. Immunocompromised status
  3. Nutritional status
  4. Age (very young & very old)
  5. Stress
38
Q
  1. Way Into the Body
A

Portal of entry is how the microorganism gets into the body

  • Ingestion
  • Open wounds
  • Inhaled
  • Injection
  • Tubes inserted into body cavities

Microbiology (PA 2205) (12 decks)

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