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Flashcards in Pathology of infections Deck (14)
1

Classes of infectious agents

Bacteria
Viruses
Fungi, including yeasts
Parasites
Prions

2

Why do infectious diseases differ?

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
Some organisms are capable of living or reproducing in very few tissues
eg influenza viruses bind to sialic (neuraminic) acid on respiratory mucosa
Some organism release products that damage only certain tissues
eg Clostridium difficile releases enterotoxins that damages large intestine mucosa

3

how do bacteria damage tissue

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
aggressins -
coagulase ← Staph aureus
streptokinase ← Strep pyogenes
collagenases ← various
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

4

How do viruses damage tissue

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

5

Fungal infections Aspergillis

a few cases of asthma
airway colonisation
aspergilloma
fungal ball in pre-existing cavity
invasive aspergillosis
immunosuppresion
hepatocellular carcinoma
aflatoxins from A flavus

6

Yeast infection - Candida

local (often called thrush)
oral or vaginal
poor hygiene
bacterial flora alterations
diabetes mellitus
systemic
immunosuppressed

7

Parasites

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

8

Protozoal diseases Amoebiasis

Entamoeba histolytica
colon colonisation causing amoebic dysentery
amoebic abscesses, eg liver

9

Protozoal diseases Giardiasis

Giardia lamblia
small intestinal infection
diarrhoea and weight loss

10

Protozoal diseases Malaria

Falciparum spp
spread by mosquitoes
colonise red blood cells
can obstruct cerebral capillaries

11

Protozoal diseases Trichomoniasis

Trichomonas vaginalis
venereal transmission

12

Flukes

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

13

Worms

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

14

Prions

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