CAUSES OF INFECTION Flashcards
what agents cause infection?
Viruses Bacteria Fungi Parasites Prions
what factors will allow infection to occur?
Barriers to infection
Environment
what are viruses?
Smaller than cellular organisms
Metabolically inert, Simple structure
Need living host cells to replicate
what do viruses infect?
animals, plants and bacteria (bacteriophages)
what are the 3 major components of a virus?
genetic material- either DNA or RNA; protein coat; lipid envelope which is derived from the host cell
what do viruses contain?
genetic material but no organelles
what do viruses rely on to reproduce?
their host’s organelles/ systems
how do viruses act?
They use surface protein(s) to bind to a cell, insert their genetic material into it
how long do viruses infect host cells for?
fo differing lengths of time
give examples of viruses
chickenpox virus
rhinovirus
hepatitis C virus
how long does the chickenpox virus act for?
can lay dormant for decades, emerging to cause shingles
how long does the rhinovirus act for?
infects hosts for days, causing a cold
how long does the hepatitis C virus act for?
causes chronic liver infection over years
do viruses differ in the severity of disease?
yes
what are severe viruses?
Ebola
SARS
what are variable viruses?
Flu - different strains of influenza virus cause differing severity
what are mild viruses?
Rhinovirus Herpes simplex (cold sore or genital sores)
what is bacteria?
Unicellular organisms
Reproduce asexually
Some move using flagella and attach via fimbriae
what does bacteria contain?
cell membrane
cell wall
no nucleus-genetic material is DNA but no bound by membrane
how is bacteria classified?
According to shape
According to ability of cell wall to take up stain
what are the different shapes of bacteria?
round- cocci
rods- bacilli
spiral
what are the different classifications that bacteria can take up stains?
gram positive
gram negative
what does the type of cell wall help determine?
structural strength of cell, and how well it can survive in the environment or in
dry conditions
what colour does gram negative stain?
stains pink
what colour does gram positive stain?
stains purple
give examples of bacterial diseases
Meningococcal sepsis
Bacterial endocarditis
Cellulitis
Streptococcal throat infection
what is fungi?
Kingdom of their own
Eukaryotes
what do fungi contain?
Cell membrane, cell wall, nucleus and cytoplasmic structures
how do fungi reproduce?
sexually or asexually
give examples of fungi
yeasts
moulds
Diamorphic fungi (can switch between types)
what are the different types of fungal infections?
mild or severe infections
give examples of mild fungal infections
thrush, athletes foot, ringworm
give examples of severe fungal infections
In the Immunocompromised
(Cryptococcal meningitis in HIV patients, Invasive candida in ICU)
Or Immune competent
what are the 3 types of parasites?
ectoparasites
endoparasites
epiparasites
what are ectoparasites?
live outside the body
give an example of ectoparasites
fleas
ticks
what are endoparasites?
live inside the body
give examples of endoparasites
worms
what are epiparasites?
a parasite which lives on another parasite
give an example of epiparasites
malaria (mosquito)
what are the 2 classes of human parasites?
Unicellular organisms- Protozoa
Worms- Helminths
why do human parasites have complex life cycles?
Many human infections are “accidental”
Life cycle often involves other animals
give an example of a parasitic disease
giardia
what does giardia cause?
Cause bloody diarrhoea
how is giardia caught?
Caught from drinking infected water
how is giardia detected?
May be seen in stool under a light microsope
Cyst form aids survival + spread
what is malaria?
One of the biggest killers worldwide
Complex life cycle
Reproduce in female anopheles mosquito
what does malaria infect?
Infect human red blood cells
what are the 4 different types of malarial parasites?
Falciparum is most severe
Different types occur in different geographical areas with some overlap
Resistance to treatment is now a problem in many areas
what are worms?
Helminths
what are the 3 different types of worms+ examples
Cestodes (tapeworms)
Trematodes (flukes)
Nematodes (round worms)
what shape are Cestodes?
Segmented, flat
what shape are Trematodes?
Unsegmented, flat
what shape are Nematodes?
Cylindrical, have digestive tract with lips, teeth and anus
give an examples of cestodes?
tapeworms
Fish, pork, beef tapeworms
what causes tapeworms?
Malabsorption
Malnutrition in chronic disease
Cysts in muscle or brain
give an example of nematodes?
round worms
what are tapeworms?
Biggest of helminth family
Huge burden of disease worldwide
what causes tapeworms?
Diarhoea / malabsorption
what are the different types of trematodes?
Flukes Lung flukes Liver flukes Pancreatic flukes Intestinal flukes Blood flukes- Schistosoma
what are prions?
Smallest infective agents known
Proteinaceous Infectious particles
what do prions lack?
Lack nucleic acid - not a ‘living organism’
how are prions caused?
Proteins fold abnormally and accumulate, mainly in neural tissue
are prions difficult to destroy?
yes
give examples of prions disease
CJD
BSE
Scrapie
Kuru
what is CJD?
fatal, degenerative neurological disease
how is CJD transmitted?
Transmitted through contaminated human growth hormone, surgical instruments and corneal grafts
what does BSE occur in?
cattle
what does Scrapie occur in?
sheep
what are the different types of defence mechanism?
skin mucus membrane stomach acid commensal microflora immune system (innate+learnt) behaviour (good hygiene practise)
