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
Venereal
Sexually transmitted diseases - mucosal contact
Discharge - easier spread = successful
And pathogen doesn’t have to survive outside the body
Transmission through the skin
Through shedding or direct - skin to skin contact
Shedding is not limited to skin - hair and nails
Direct contact much more common
Example = warts, fungal infections, S. aureus
Transmission through blood
Requires exposure to blood
Common in certain demographics - healthcare, IV drug addicts
Example - hepatitis, HIV
Vertical spread
Occurs between mother to baby through the placenta
- At childbirth
- Through milk
- Germline
Indirect contact
Spread from one host to another through fomites
What are fomites?
Inanimate objects that are used to transfer pathogens to new host
Vehicle transmission
Through air, water, food and bodily fluids
Can spread diseases through long distances
Vector transmission
In the form of insects, ticks and mites
Biological vectors - vector acts as a most for the multiplication of the pathogen. E.g, fleas and plague, mosquitoes and malaria
Mechanical vectors - insects carry the pathogen passively
Control of air transmission
Control not easy, nor cheap
HEPA filtration
Lab containment
Face masks
