Infectious diseases

Question 1

3 ways that organisms can spread disease

Answer 1

• some organisms are capable of living in any tissue eg. staph aureus makes coagulases
• some organisms can release products that can wide spread damage eg. E.coli produces endotoxins that can spread via the bloodstream
• some organisms are capable of living and reproducing in very few tissues eg. influenza, clostridium

Question 2

Why do infectious diseases differ?

Answer 2

clostridium difficile releases enterotoxins that damage large intestine mucosa
clostridium botulinum releases a toxin ingested with food
vibrio cholera activates cAMP = active loss of fluid from intestinal lining

Question 3

How do bacteria damage tissues?

Answer 3

by aggressins which are non-toxic material that enhance survival of an organism
- coagulase (Staph aureus)
promotes blood clotting on surface and forms a protective coat around itself
- streptokinase (strep pyrogenes)
promotes plasminogen activation, decreases clotting and healing
- collagenases
break down ECM framework

Question 4

How do viruses damage tissues?

Answer 4

direct cytopathic effects eg influenza, hep A
immune reactions eg hep B and C
incorporation of viral genes into host genome eg variety of oncogenic viruses

Question 5

Fungal infections

Answer 5

eg. Aspergillus
can cause asthma due to airway colonisation
aspergillomas (fungal ball in pre-existing cavity)
invasive aspergillosis (immunosuppression)
hepatocellular carcinoma (aflatoxins from A flavus)
Yeast infections
eg. Candida albicans
local (thrush)
- oral or vaginal
- poor hygiene
- bacterial flora alterations
- diabetes mellitus
systemic
- immunosuppressed

Question 6

Parasites - protozoal diseases

Answer 6

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
- spread by mosquitos 
- colonise red blood cells
- can obstruct cerebral capillaries
Trichomoniasis -
Trichomonas vaginalis
- venereal transmission

Question 7

Parasites - flukes

Answer 7

Schistomsomiasis
Schistosoma
- life cycle involves human and water snails
- granulomata in urinary bladder or liver

Question 8

Parasites - worms

Answer 8

Roundworms -
- enterobius vermicularis  = threadworms
Tapeworms - 
- Diphyllobothrium latum
- fish tape worm causing vitamin B12 deficiency
-   Echinococcus granulosus
- dog tapeworm causing liver cysts

Question 9

Prions

Answer 9

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

Question 10

Sepsis

Answer 10

overwhelming response to infection
body temperature above 38.3 or below 36
HR higher than 90 bpm
respiratory rate higher than 20 breaths per min
severe - 
- significantly decreased urine output 
- abrupt change in mental status
- decreased platelet count
- difficulty breathing
- abnormal heart pumping function
- abdominal pain
septic shock = hypotension

Question 11

Causes of sepsis

Answer 11

pneumonia
abdominal infection
kidney infection
bacteraemia