Week 11 - Pathology Of Infections

Question 1

Why do infectious diseases differ and give examples?

Answer 1

• some organisms are capable of living in any tissue
• some organisms are capable of releasing products that damage widely
• some organisms are capable of living or reproducing in very few tissues
• some organisms release products that damage only certain tissues

Question 2

How do bacteria damage tissue?

Answer 2

-pili on the surface attach to cell walls, allowing adhesion
-exotoxins
-endotoxins
-agressins
-immune reactions
-immune cross-reactions
-cell-mediated immunity
-

Question 3

What are exotoxins produced by and what do they do?

Answer 3

• produced by intact bacteria

- typically have specific effects

Question 4

What are endotoxins produced by and what do they do?

Answer 4

• components of cell walls
• trigger complement cascade
• trigger coagulation cascade
• induce interleukin 1, causing fever

Question 5

What are agressins produced by and what do they do? (Give examples)

Answer 5

-produced by bacteria

• coagulase - staph aureus
• streptokinase - strep pyogenes
• collagenases - various

Question 6

How do immune reactions from bacteria damage tissue?

Answer 6

-antibody-antigen complexes deposited in glomerulus or skin –> glomerulonephritis and cutaneous vasculitis

Question 7

Give an example of how immune cross-reactions from bacteria damage tissue

Answer 7

-e.g. Streptococcal sore throat leading to rheumatic fever

Question 8

How to viruses damage tissue? (Give examples)

Answer 8

• direct cytopathic effects (influenza virus, hep A)
• immune reactions (hep b and c, diabetes - type 1)
• incorporation of viral genes into host genome (variety of oncogenic viruses)

Question 9

Name a fungal infection and how it may occur/affect in the body in different ways

Answer 9

Aspergillus spp

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

Question 10

Name a yeast infection and how it may occur/affect in the body in different ways

Answer 10

Candida albicans (thrush)

Local - oral/vaginal, poor hygiene, bacterial flora alterations, diabetes mellitus

Systemic - immunosuppressed

Question 11

Name some parasites

Answer 11

Protozoa
Trematodes (flukes)
Nematodes (round worms)
Cestodes (flatworm or tapeworms)

Question 12

What are Protozoa and what diseases do they cause?

Answer 12

Parasite

• amoebiasis - (entamoeba histolytica), colon colonisation causing amoebic dysentery, amoebic abscesses eg liver
• giardiasis - (giardia lamblia, small intestinal infection, diarrhoea and weight loss
• malaria - (falciparum spp), mosquitoes spread, colonise RBC, can obstruct cerebral capillaries
• trichomoniasis - (trichomonas vaginalis), venereal (sexually) transmission

Question 13

What are flukes (trematodes) and what diseases do they cause?

Answer 13

Parasite

• schistosomiasis (schistosoma spp - flukes), life cycle involves humans and water snails
• granulomata - in bladder (S haematobium) or in liver (S mansoni/japonicum)

Question 14

What are flukes (trematodes) and what diseases do they cause?

Answer 14

Parasites

• round worms - (enterobius vermicularis - thread worms)
• tape worms - (diphyllobothrium latum) - fish tapeworm causing vit b12 deficiency, (echinococcus granulosus) - dog tapeworm causing liver cysts

Question 15

What are prions?

Answer 15

Infectious particles with no DNA or RNA

Question 16

What can prions cause?

Answer 16

• transmissible spongiform encephalopathy
• Creutzfeldt-Jakob disease
• exogenous protein causes conformational changes in endogenous protein

Question 17

Which organ is more commonly exposed to bacteria than any other?

Answer 17

The lungs

Question 18

What are the classes of infectious agents?

Answer 18

Bacteria 
Viruses 
Fungi - including yeasts
Parasites
Prions