23 PATHOLOGY OF INFECTIONS Flashcards

1
Q

Classes of infectious agents

A
Bacteria
   Viruses
   Fungi, including yeasts
   Parasites
   Prions
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2
Q

Why do infectious diseases differ?

A

Some organisms are capable of living in any tissue
eg Staph aureus makes coagulases
Some organism are capable of release products that damage widely
eg Escherichia coli produces endotoxins that spread via the blood stream

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3
Q

Why do infectious diseases differ?

A

Some organisms are capable of living or reproducing in very few tissues
influenza viruses bind to sialic (neuraminic) acid on respiratory mucosa
Aspergillus spp sporulate only when in contact with air
Clostridium spp require hypoxic conditions

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4
Q

Why do infectious diseases differ?

A

Some organism release products that damage only certain tissues
Clostridium difficile releases enterotoxins that damages large intestine mucosa
Clostridium botulinum releases a toxin ingested with food
Vibrio cholerae toxin activates cyclic ATP, causing active loss of fluid from intestinal lining

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5
Q

How bacteria damage tissue

A
pili on the surface attach to cell walls, allowing adhesion
   exotoxins
   produced by intact bacteria
   typically have specific effects
   endotoxins
   components of cell walls
   trigger complement cascade
   trigger coagulation cascade
   induce interleukin 1, causing fever
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6
Q

How bacteria damage tissue

A
aggressins
   coagulase ← Staph aureus
   streptokinase ← Strep pyogenes
   collagenases ← various
   etc, etc
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7
Q

How bacteria damage tissue

A

immune reactions
antibody-antigen complexes deposited in glomerulus or skin → glomerulonephritis and cutaneous vasculitis
immune cross-reactions
eg streptococcal sore throat leading to rheumatic fever
cell-mediated immunity
eg tuberculosis

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8
Q

How viruses damage tissue

A

direct cytopathic effects
influenza virus; hepatitis A; etc, etc
immune reactions
hepatitis B and C; diabetes mellitus type 1 (perhaps)
incorporation of viral genes into host genome
variety of oncogenic viruses

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9
Q

Fungal infections

A
Aspergillus spp (as an example)
   a few cases of asthma
   airway colonisation 
   aspergilloma
   fungal ball in pre-existing cavity
   invasive aspergillosis
   immunosuppresion
   hepatocellular carcinoma
   aflatoxins from A flavus
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10
Q

Yeast infections

A
Candida albicans (as an example)  
   local (often called thrush)
   oral or vaginal
   poor hygiene
   bacterial flora alterations
   diabetes mellitus
   systemic
   immunosuppressed
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11
Q

Parasites

A

Protozoa
Trematodes (flukes)
Nematodes (roundworms)
Cestodes (flatworm or tapeworms)

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12
Q

Protozoal diseases

A
Amoebiasis
   Entamoeba histolytica
   colon colonisation causing amoebic dysentery   
   amoebic abscesses, eg liver
   Giardiasis
   Giardia lamblia
   small intestinal infection
   diarrhoea and weight loss
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13
Q

Protozoal diseases

A
Malaria
   Falciparum spp
   spread by mosquitoes
   colonise red blood cells
   can obstruct cerebral capillaries
   Trichomoniasis
   Trichomonas vaginalis
   venereal transmission
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14
Q

Flukes

A

Schistosomiasis
Schistosoma spp (flukes)
life cycle involves humans and water snails
granulomata in urinary bladder (S haematobium) or liver (S mansoni or japonicum)

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15
Q

Worms

A
Roundworms
   Enterobius vermicularis 
   threadworms
   Tapeworms
   Diphyllobothrium latum
   fish tapeworm causing Vit B12 deficiency
   Echinococcus granulosus
   dog tapeworm causing liver cysts
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16
Q

Prions

A

infectious particle with no DNA or RNA
transmissible spongiform encephalopathy
Creutzfeldt-Jakob disease
exogenous protein causes conformational changes in endogenous protein

17
Q

AN EXAMPLE

A

RESPIRATORY INFECTIONS AND ASSOCIATED CONDITIONS

The lung is more commonly exposed to bacteria than any other organ

18
Q

Major defences

A
nasopharyngeal filtering
   "hair trap; mucus in nasal cavity
   mucociliary apparatus
   mucus in bronchi; cilia on columnar cells
   coughing
   resident alveolar macrophages
19
Q

Interference with defences

A
loss or suppression of cough reflex
   interference with cilia
   changes in mucus 
   poor alveolar macrophage function 
   pulmonary oedema 
   bronchial obstruction 
   nosocomial infection
20
Q

Loss or suppression of cough reflex

A
anaesthetic agents
   neurological disorders 
   eg motor neuron disease
   drugs 
   eg opiates
   chest or abdominal pain 
   eg rib fractures, surgery
   coma
21
Q

Interference with cilia

A

smoking
hot gases
viral disease
inherited ciliary dyskinesias

22
Q

Changes in mucus

A

dehydration
cystic fibrosis
chronic bronchitis

23
Q

Interference with defences

A
Poor alveolar macrophage function
   alcohol
   tobacco
Pulmonary oedema
   left ventricular failure
Bronchial obstruction
   foreign body
   tumour
Nosocomial infection