Pathology of infections

Question 1

Classes of infectious agents

Answer 1

Bacteria
   Viruses
   Fungi, including yeasts
   Parasites
   Prions

Question 2

Why do infectious diseases differ?

Answer 2

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

Question 3

how do bacteria damage tissue

Answer 3

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

Question 4

How do viruses damage tissue

Answer 4

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

Question 5

Fungal infections Aspergillis

Answer 5

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

Question 6

Yeast infection - Candida

Answer 6

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

Question 7

Parasites

Answer 7

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

Question 8

Protozoal diseases Amoebiasis

Answer 8

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

Question 9

Protozoal diseases Giardiasis

Answer 9

Giardia lamblia
small intestinal infection
diarrhoea and weight loss

Question 10

Protozoal diseases Malaria

Answer 10

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

Question 11

Protozoal diseases Trichomoniasis

Answer 11

Trichomonas vaginalis

venereal transmission

Question 12

Flukes

Answer 12

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

Question 13

Worms

Answer 13

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

Question 14

Prions

Answer 14

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