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Pathology 1 > Principles of Infection > Flashcards

Principles of Infection Flashcards

1
Q

What are the 2 types of parasites?

A

Commensal - can be opportunistic

Pathogen - conditional

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2
Q

Name the sterile parts of the body

A

Lower respiratory tract
Blood, joint and subcutaneous connective tissue
Female upper genital tract
Urinary tract 9 (not distal urethrae)
CNS including CSF & eye
Other viscera e.g. liver, spleen and pancreas

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3
Q

What is the result of infections?

A

Infections cause harm to the host causing disease

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4
Q

What are the 4 Koch’s postulates?

A

Gene theory states that a microorganism must be:

  1. Present in every case of the infection
  2. Cultured from cases in vitro
  3. Reproduce disease in animals
  4. Isolated from infected animal
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5
Q

Describe a chronic infection

A

Slower onset / post acute
May still have major locally / systemic symptoms
Has a chronic inflammatory response when host doesn’t succumb immediately to infection
but can’t clear the infection
e.g. Tuberculosis or chronic osteomyelitis

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6
Q

What are pathogens?

A

Microbes that cause disease often with small numbers ia natural routes, despite natural barriers and immune defences

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7
Q

Describe the key features of an Acute infection

A

Rapid onset
Major local & systemic symptoms
Acute inflammatory response
e,g. streptococcus polygenes or straphylococccus aureus

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8
Q

What are the host’s defences?

A

Innate and adaptive immune system

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9
Q

What is a full pathogen?

A

Initiates infection via neutral route despite immune defences

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10
Q

What microbial and host mechanisms are kept in balance?

A

Pathogenic mechanisms
- adhesion, toxins, capsule

Host defensive mechanisms
- natural barriers, defensive cells, complement

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11
Q

What are strict pathogens?

A

Microbes that will always cause disease e.g Bacillus anthracis (anthrax)

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12
Q

What are the body’s natural barriers?

A
  • skin
  • eyes
  • GI tract
  • lungs
  • Gut
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13
Q

Give an example of a toxin mediated acute infection

A 
Diphteria (cornyebacterium diphtheriae 
Tetanus 
- gram +ve rods 
- terminal drumstick spores 
- anaerobe , soil dweller 
- opisthotorius = severe hyperextension
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14
Q

What is saprophyte?

A

Saprophyte is a free living organism living on decaying organic matter

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15
Q

How is inflammation regulated?

A

Inflammation is an ordered process that is regulated via

  • Vasodilation
  • Oedema
  • Complement activation
  • Clotting
  • PMNs recruitment
  • Mast cell degradation
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16
Q

How do host cells respond to pathogens and commensals?

A

Normally the host cell will manifest an inflammatory response to a pathogen, but not to a coloniser at a normal non sterile site

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17
Q

What is asymptomatic infection?

A

Pathogenic microbe infection (not commensal or normal flora)
- mild / no inflammatory response
- damage to host is mild / not at all
e.g. chlamydia trachornitis (urethral in males, cervical in women)
50% men asymptomatic
80% women symptomatic

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18
Q

What is inflammation?

A

Response to tissue injury

Brings serum molecules and cells to infection sites

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19
Q

What are latent infections?

A

A virus that never leaves the body and can be reactivated

e.g. chocken pox in children causes shingles in adults (varicella zoster -> herpes zoster)

20
Q

What are conditional pathogens?

A

Pathogens causing disease only under certain conditions

21
Q

What is parasitism?

A

Pathogens that actually cause disease

22
Q

What is the role of inflammation?

A

Increases blood supply
Increases capillary permeability
Cell (polymorphs/macrophage) migration from blood to tissue

23
Q

What are the symptoms of infection?

A

Local

  • redness, swelling, warmth, pain, loss of functions
  • pus (pyogenic infection)

Systemic
- Fever, rigors, chills, tachycardia, tachypnoea (increased breathing rate)

24
Q

What are virulence factors?

A

Molecules produced by pathogens which add to the effectiveness of the pathogen to:

  1. evade immune responses
  2. enter / exit host cell
  3. immunosuppression
  4. colonisation
  5. obtaining nutrients from host
25
Q

How can commensals cause disease in certain tissues?

A

In healthy individuals, commensal microbes (normal flora) do no harm
They cause colonisation not infection
But if the host’s defences are weakened (immuno-compromised) infection may occur
-> opportunistic infection

26
Q

What are the body’s non specific barriers?

A

Physical conditions , Microflora, Bile & Mucin
Lysozymes, lactoferrin & tight junctions
Cryptidins
Cilliated epithelia
Toxic lipids & lactoperoxidases
Intraepithelial lymphocytes & phagocytes

27
Q

What are cross reactive antigens or cross immunity?

A

When immunity to one form of pathogen is effective in protecting against an antigenically
similar but different organism
e.g. Streptococci and Rheumatic heart disease

28
Q

Name examples of commensals becoming pathogens in different areas of the body

A

Staphylococcus aureus

  • Commensal in nose
  • Pathogen in post operative wound infections

Escherichia Coli

  • Commensal in GI tract
  • Pathogen in Urinary tract causing UTI

Staphylococcus epidermis

  • Commensal on skin
  • Pathogen in IV lines causes blood stream infections
29
Q

What are endotoxins?

A

Components of the bacterial cell wall => drive a massive immune response

30
Q

What is the consequence of inflammation?

A

Can cause tissue damage

31
Q

What are virulent mcirobes?

A

Highly pathogenic microbes

32
Q

Give an example of an opportunistic infection

A

HIV causing a decline of CD4

33
Q

What are the 3 different types of infection?

A

Local - surface infection (wounds)
Invasive - Penetrate barriers & spread
Systemic - Via blood to other sites

34
Q

What does the adaptive immune response involve?

A

T cells and antibodies

35
Q

What is commensalism?

A

No harm done to either side, usually one side benefits - these don’t cause disease

36
Q

What is virulence?

A

Virulence is the degree to which a microbe causes disease depending on

  • virulent strains
  • gene content alters phenotype
  • host susceptibility
37
Q

How are blood and tissue defences initiated?

A

Defences of blood and tissue involve tissue damage and are controlled by feedback mechanisms e.g inflammation

38
Q

What are the body’s specific barriers?

A

Phagocytes: monocytes, macrophages, PMNs & neutrophils
Complement
Acute Phase proteins released by the liver
Transferrin
=> these cause macrophage activation

39
Q

When do commensals become Pathogens?

A

At different sites, due to immunosuppression allowing them to bypass defences

40
Q

What are the stages of infection?

A
  • Acquisition from spread
  • Colonisation
  • Penetration and spread
  • Immune evasion
  • Tissue damage
  • Shedding & transmission
  • Resolution

(not all microbes require all these stages)

41
Q

How does Whooping cough arise?

A

Toxin mediated disease (bordetella pertussis)

  • invasive adenylate cyclase
  • lethal toxin (dermonecrotic) superantigen
  • trachaeal cytotoxin
  • pertussis Toxin (PTx)
42
Q

What is the role of virulence factors during infection?

A

Aid bacterium adhere and colonise in host
Promote tissue damage
e.g. M protein of streptococccus pyogenes acts as
adhesion and structural components of bacterial cell
wall

43
Q

How do Neisserie Gonorrhae cause gonorrhae?

A

Fimbrae allow bacteria to adhere to P blood group antigen of uroepithelial cells

44
Q

What is the net effect of adhesion of pathogens to host cells?

A

Multiplication at mucosal surface
Localised immune activation
Survival & transmission

45
Q

How are infections spread?

A

Direct contact
Indirect Contact
Airborne
Blood products

46
Q

How does pathogen adhesion occur?

A

Via surface adhesion structures of bacteria/virus
Attach to mucosal surfaces via specific receptors on host cells
e.g. Influenza virus A - haemoglutinin & sialyoligosaccharides
HIV & CD4 + CXRC5 surface proteins of CD4 cells
Allows specific cell entry

Pathology 1 (20 decks)

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