22. PATHOLOGY OF INFECTIONS Flashcards
Classes of infectious agents
Bacteria Viruses Fungi, including yeasts Parasites Prions
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
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
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
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
How bacteria damage tissue (2)
aggressins coagulase ← Staph aureus streptokinase ← Strep pyogenes collagenases ← various etc, etc
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
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
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
Yeast infections
Candida albicans (as an example) local (often called thrush) oral or vaginal poor hygiene bacterial flora alterations diabetes mellitus systemic immunosuppressed
Parasites
Protozoa
Trematodes (flukes)
Nematodes (roundworms)
Cestodes (flatworm or tapeworms)
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
Protozoal diseases (2)
Malaria Falciparum spp spread by mosquitoes colonise red blood cells can obstruct cerebral capillaries Trichomoniasis Trichomonas vaginalis venereal transmission
Flukes
Schistosomiasis
Schistosoma spp (flukes)
life cycle involves humans and water snails
granulomata in urinary bladder (S haematobium) or liver (S mansoni or japonicum)
Worms
Roundworms Enterobius vermicularis threadworms Tapeworms Diphyllobothrium latum fish tapeworm causing Vit B12 deficiency Echinococcus granulosus dog tapeworm causing liver cysts
