Infectious Disease Flashcards
What is the definition of aetiology pathogenesis microbemia viremia fungemia bacteremia
aetiology - cause of the disease
pathogenesis - step by step development of the disease
microbemia - presence of bacteria in the blood and microbe specified
example
viremia - virus
fungemia - fungi
bacteremia - bacteria
What is the difference between specific and non-specific defence mechanisms?
specific
- white blood cells = B and T lymphocytes
- humoral and cell mediated immunity
- antibodies aid in the recognition of a previous infection used in vaccine situations
non-specific
- skin and mucous membranes
- white blood cells, inflammation, defensive proteins
How are some infections eradicated? What are the issues with eradicating infections?
eradicated/reduced due to
- vaccines
- antibiotics
- effective public health measures
problems
- resistance to antibiotics
- bioterrorism
- new infection
What are the steps required for successful infection?
transmission, adhesion, penetrate, spread, survival in host
1 - transmission = disease must be spread
2 - adhesion = pathogen needs to attach itself to the host (adhesion = forces between different surfaces)
3 - penetration - pathogen must be able to penetrate the host defence mechanism or the cell
4 - spread - there must be a certain number of bacteria to cause infection
5 - survival in the host
What is epidemiology? What are the factors affecting epidemiologic triangle?
epidemiology - looks at the incidence, distribution and control of diseases
agent
- infectivity, pathogenicity, virulence, antigenic stability
host
- age, sex, genotype, behaviour, health status
environment
- weather, housing, geography, occupational settings
How do bacteria cause infection? How do they cause tissue injury?
endotoxins
exotoxins
siderophores
What are endotoxins? What is the structure?
omnipresent in the environment
endotoxins - toxic lipopolysaccharide components of the outer membrane of the gram negative bacteria
secured to the outer membrane and released after lysis of the bacteria = disintegration of the cell (dead) by rupture of the cell wall
oligosaccharide side chains - serotype antigens (specific to the individual)
core polysaccharide
lipid A - toxic moiety
What are the biological effects of endotoxins? What are examples of endotoxins?
biological effects
- pyrogenicity, leukopenia, blood pressure
these could culminate/result in sepsis (damage to organs) and lethal shock (drop in blood flow)
example
- salmonella spp
- E.coli
What are exotoxins?
most toxic substance known
exotoxins are proteins released from viable (live) bacteria
produced by gram positive and negative bacteria cells
they can be grouped in 3 categories
- neurotoxins = botulinum toxin from Clostridium botulinum
- cytotoxins = diphtheria toxin from Corynebacteriumdiphtheriae
- enterotoxins = shiga-like enterotoxin from E. coli
What is the difference between endotoxins and exotoxins?
endotoxin
- are the lipid portion of the lipopolysaccharide
- part of the outer membrane of the cell wall of gram negative bacteria
- produced after lysis of the bacteria = dead bacteria
exotoxins
- produced by viable bacteria = live bacteria
- proteins produced inside pathogenic bacteria
- proteins are secreted or released into the medium
What are the methods of transmission?
contact
- spread by airborne droplets (less than 3 feet)
- transmission directly from source to susceptible host
- pseudomonas organisms
common vehicle
- transmission by a common inanimate vehicle, with multiple cases resulting from direct exposure (food and water)
- salmonellosis
air
- by droplet nuclei/dust (less than 3 feet)
- tuberculosis
vector
- arthropods are vector, internalised or not
- spreads/carries the disease
- malaria
Why is route of entry important?
entry site is important to each individual pathogen
- decides the infection type
- decides the target tissue
once infection is established, different pathogens will go on to infect and multiply in different areas of the body or remain at the site of entry
What are virulence factors?
virulence factors
- pathogens ability to infect or damage as host immune system is determined by its virulence factors
- produced by bacteria, fungi, viruses and protozoa that increase their effectiveness
What are the types of virulence factors?
adherence and colonisation factors
- attachment mechanisms = pili
- E.coli, salmonella spp
invasion factors
- mechanisms that enable the bacteria to evade eukaryotic cells
- chlamydia spp
capsules and other surface components
- capsules are protective - resistant to phagocytosis and intracellular killing by the host cell
capsular antigens and lipopolysaccharides play a role inn host defence resistance
- salmonella typhi
How do skin infections occur?
organisms usually enter through a break in the skin
- insect bite
many systemic infections involve skin symptoms caused by the pathogens or the toxins
- measles
most skin infections cause (signs of inflammation)
- erythema - redness of skin
- oedema - swelling
infections may be primary or secondary
