Principles of Infection 2 Flashcards
Steps to becoming unwell with an infection
- Transmission
- Infection
- Pathogenicity
- Virulence
what happens at the transmission step?
host has to acquire the organism
what happens at the infection step?
the organism has to reproduce inside the host
what happens at the pathogenicity step?
organism interacts with the host in a way that causes diseases
what happens at the virulence stage?
organism causes a disease of varying severity
example of air-borne spread
aerosols or droplets from cough etc
examples of person to person spread
direct e.g. skin infection, STDs
Examples of faceo-oral spread
most often via food/ water e.g. cholera
examples of consumption of infected material transmission
e.g. salmonella, tapeworm
example of vector-borne disease transmission
mosquitos spread malaria & zika infection
example of endogenous infection transmission
from movement of own microbiome e.g. colonic bacteria to urine
example of direct inoculation transmission
e.g. open fracture, bite form infected animal
how do microorganisms cause disease?
indirect damage by host immune response and direct damage by the pathogen
How does the host immune response cause indirect damage?
- inflammation causes tissue damage & lost of normal function
- systemic response to infection can cause organ failure and death
How does a pathogen cause direct damage?
- viral reproduction causes cell lysis ( cell breakdown)
- Bacteria secrete toxins causing cell damage
How do microorganisms evade the immune system?
- Adhere (stick) to the epithelium
- Invade epithelial cells / cross epithelial barrier
- Evade innate immune cells
- Evade adaptive immune cells and antibodies
define virulence factors:
components or structure of microorganisms that helps in establishment of disease or infection (essentially to assist microorganism to colonise)
virulence factors include factors that allow microorganisms to:
- Adhere to and invade host tissues
- Evade host defences
- Proliferate in the host
- Cause damage
- Produce toxins
- host- pathogen interaction
tiny hairs on bacteria are called?
pili
Define adhesins
(on bacteria that) allows them to stick onto epithelial cells & stops them from being swept away
Define adhesins and pili
pili- tiny hairs (on bacteria that) and adhesins allow them to stick onto epithelial cells & stops them from being swept away
Some bacteria secrete enzymes which do what?
degrade the host molecules by attacking the epithelial barrier (e.g. breaking down tight junctions)
secretion of enzymes allows bacteria/ viruses to?
get past the barrier and then sit in the interstitial/ extracellular fluid however can get into epithelial cells or immune cells (e.g. tuberculosis)
Once bacteria/virus has invaded the cell, they will do what?
set of signalling molecules that will propagate this and make this process worse
Steps to adherence and invasion
- Bacteria has anatomical structure (pili and adhesins)
- Some bacteria secrete enzymes, attacking the barrier
- Can however get into epithelial or immune cells
- once invaded it will set of signalling molecules
Examples of evade host defences in bacteria
capsule, cell wall and toxins
Examples of evade host defences in viruses
antigenic drift, antigenic shift
Function of capsule in bacteria
-protects bacteria from host immune response and antibiotics
‘frustrated phagocytosis’ enhances?
the inflammatory response
define frustrated phagocytosis
occurs when phagocytic cells are exposed to an opsonised surface and spread as if trying to engulf it
Function of cell wall in bacteria
- contains endotoxins - excreted after cell death & lysis
- Activate a pathway of events weakening host (septic shock)
define antigenic drift
small changes in viral antigens due to point mutations in genes
define antigenic shift
Major changes in vial antigens due to gene reassortment
virulence factors are determined how?
genetically
Horizontal gene transfer enables?
bacteria to respond and adapt to their environment rapidly by acquiring large DNA sequences from another bacterium in a single transfer
Horizontal gene transfer therefore means bacteria can?
share antibiotic resistance genes
genes disseminated by horizontal transfer allows?
bacteria to share common pathogenic mechanisms and antibiotics resistance
Strep A is transmitted how?
person- person spread, air- borne
Infection by Streptococcus A is what type of bacteria? shape? oxygen conditions?
Gram positive
Cocci shape
Aerobe
Pharyngitis also known as
sore throat
scarlet fever also known as?
rash
How does sore throat (pharyngitis) cause indirect damage by host immune response?
Bacteria invade throat cells
- immune system fights bacteria causing inflammation
How does scarlet fever cause direct damage by the pathogen?
Bacteria in the throat make a toxin that enters the body and causes a skin rash
How does Invasive group A strep disease by direct damage by the pathogen?
Bacteria evade the immune system and spread to a normally sterile body site- toxin causes shock and multiorgan failure
Virulence of sore throat, rash, Strep A?
Sore throat: mild- very common
Rash: moderate - less common
Strep A : severe - very rare
what causes influenza?
viruses: several types cause infection in humans : influenza A, B & C
How is Influenza highly transmissible?
air- borne, person to person direct & indirect contact, can also come from animals and birds
How does Influenza infect?
viruses enter cells of respiratory tract and proliferate
Pathogenesis of Influenza via direct damage
-Viruses directly damage respiratory cells by lysis during reproduction
Pathogenesis of Influenza via indirect damage
-Viruses cause indirect damage by triggering an immune response which causes damage and symptoms
Viiruses make a lot of ‘mistakes’ during replication, by creating?
new strains
SARS- CoV-2 is what type of virus
RNA virus
Why do RNA viruses have a high mutation rate?
RNA viruses dont have proof reading mechanisms to correct mistakes
define a variant
where the viral genome contains one or more mutations
List ways some variants confer advantages on the virus
- Increase transmissibility
