When Microorganisms Cause Infection Flashcards
Pathogenicity
The ability to cause disease
Virulence
A measure of pathogenicity
Contamination
The presence of microorganisms in/on the body
Infection
Invasion of the body by a pathogen
Host defence
- First line = non specific → defences against any pathogen
- Second line = specific for bacteria or viruses
- Third line = specific for a particular pathogen
First line of defence
- Innate
- Present all the time
- Non-specific
- Physical and chemical
- Most important- skin
- Commensal flora play an important part
E.g, stomach acidity (pH 2) inhibits microbial growth & blood proteins inhibit microbial growth, etc.
Second line of defence - Inflammation
Purpose = to localise infection (easier to destroy), neutralise toxins , repair damaged tissue
Non -specific response to tissue damage resulting from various causes
Phagocytosis
The 5 cardinal signs of acute inflammation
- Redness (rubor) - increased blood flow to the area
- Swelling (tumor) - increased blood flow and no drainage
- Pain (dolor) - if tumor has affected a nerve
- Heat (calor) - more blood flow
- Loss of function ( functio laesa)
Third line of defence - immune response
- Innate immunity
- Antibody -mediated
- Cell mediated
Why do pathogens need to spread
To survive.
What does transmission depend on?
- The number of microorganisms shed
- Microorganism’s stability in the environment
- Number of microorganisms required to infect new host (infective dose)
The portals of entry
Ear
Conjunctiva of eye
Nose
Mouth
Placenta
Vagina
In males: Penis
Urethra
Anus
Broken skin
Insect bite
The portals of exit
Eyes → tears
Nose → secretions
Mouth → saliva, sputum
In females: Mammary glands (milk, secretions)
Vagina → secretions, blood
Urethra → urine
Seminal vesicles → semen and lubricating secretions
Anus → faeces
Skin → flakes
Broken skin → blood
Ear → ear wax
Reservoirs of infection - where do they come from?
In order for a disease to persist in a community it must have a reservoir or continual source of organisms (can be living or non-living)
Reservoirs of infection - living
Human reservoirs - aids, diphtheria, hepatitis, common cold
Animal reservoirs - zoonoses, rabies
Insects - Lyme disease
Zoonoses
- Cross of the species barrier - one species infects another
- Most of the infection spread is within the same species
- Source = vertebrate
- Can lead to an epidemic due to lack of immunity
E.g, Covid
Inanimate reservoirs
Soil
Air
Food
Water
Types of transmission
Contact transmission - direct contact, indirect contact + droplet transmission
Vehicle transmission
Vector transmission
Contact transmission
Direct - syphillis, gonorroheae, herpes
Indirect - enterovirus infection, measles
Droplet (less than 1 meter) - whooping cough, strep throat
Vehicle transmission
Airborne - influenza, tuberculosis,chickenpox
Water-borne (fecal oral infection) - cholera, diarrhoea
Food-borne - hepatitis, food poisoning, typhoid sever
Vector transmission
Biological vectors - malaria, plague, yellow fever
Mechanical vectors - E.coli, diarrhoea, salmonellosis
Types of person to person transmission
Respiratory or salivary
Venereal
Faecal - oral route
Transmission from the Respiratory Tract
Helped by sneezing + coughing
Sneeze = 20,000 droplets → if carrying cold virus, each one will contain virus particles
Helped by crowded conditions
E.g mycobacterium tuberculosis
Faecal oral route
Large numbers in faeces + poor hygiene
Controlled by public health measures:
- Adequate sewage disposal, purified water
- Cholera, typhoid
