22. PATHOLOGY OF INFECTIONS Flashcards Preview

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Flashcards in 22. PATHOLOGY OF INFECTIONS Deck (23)
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1

Classes of infectious agents

Bacteria
Viruses
Fungi, including yeasts
Parasites
Prions

2

Why do infectious diseases differ? (1)

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

3

Why do infectious diseases differ? (2)

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

4

Why do infectious diseases differ? (3)

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

5

How bacteria damage tissue (1)

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

6

How bacteria damage tissue (2)

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

7

How bacteria damage tissue (3)

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

8

How viruses damage tissue

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

9

Fungal infections

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

10

Yeast infections

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

11

Parasites

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

12

Protozoal diseases (1)

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

13

Protozoal diseases (2)

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

14

Flukes

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

15

Worms

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

16

Prions

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

17

AN EXAMPLE

RESPIRATORY INFECTIONS AND ASSOCIATED CONDITIONS

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

18

Major defences

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

19

Interference with defences

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

20

Loss or suppression of cough reflex

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

21

Interference with cilia

smoking
hot gases
viral disease
inherited ciliary dyskinesias

22

Changes in mucus

dehydration
cystic fibrosis
chronic bronchitis

23

Interference with defences

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