Pathogens and defences
What causes disease
- A pathogen is an organism that causes disease.
- A transmissible disease is one whose pathogen can pass from one host to another.
- Bacteria and viruses are common pathogens.
Practice
A pathogen is:
A pathogen is a disease-causing organism, such as a bacterium or virus.
How pathogens spread
- By direct contact — for example through blood or other body fluids.
- Indirectly — from contaminated surfaces, food, water, animals, or the air.
Practice
Which is an example of INDIRECT transmission?
Indirect transmission is via contaminated food, water, surfaces or air; direct is through body contact/fluids.
The body's defences
- skin — a barrier covering the body.
- hairs in the nose — trap dust and pathogens in the air.
- mucus — sticky liquid in the airways that traps pathogens.
- stomach acid — kills most pathogens in food.
- white blood cells — find and destroy any pathogens that get inside.
Practice
Which of these are the body's natural defences? (Choose all that apply.)
Skin, mucus and stomach acid are natural defences; vaccination is medical help, not a natural barrier.
Controlling the spread
- a clean water supply, so drinking water carries no pathogens.
- hygienic food preparation and washing hands.
- proper waste disposal and sewage treatment.
Practice
A clean water supply and sewage treatment help control the spread of disease.
Clean water and proper sewage treatment stop pathogens contaminating drinking water and food.
You've got it
Key idea
- pathogen = organism that causes disease; transmissible = passes between hosts (direct or indirect)
- five defences: skin, nose hairs, mucus, stomach acid, white blood cells
- public health controls spread: clean water, hygiene, sewage treatment