Learning focus
Build precise biological explanations, interpret diagrams and data, and connect structure, process, health and practical evidence.
Definitions
A pathogen is a disease-causing organism. A transmissible disease is one in which the pathogen can pass from one host to another. Pathogens include bacteria, viruses, fungi, protoctists and parasites, but the specific examples in this topic are malaria, HIV and cholera.
Direct transmission
Direct contact includes skin contact, sexual contact and transfer through blood or other body fluids. Transmission requires an appropriate route; ordinary social contact does not spread every pathogen.
Indirect transmission
Pathogens can spread through air droplets, contaminated food or water, contaminated surfaces, animals or vectors. The best control measure depends on the route.
Body barriers
Intact skin forms a physical barrier. Nasal hairs trap larger particles. Mucus traps particles and pathogens, while cilia move it away from lungs. Stomach acid kills many swallowed microorganisms.
Breaking transmission
Control may remove the pathogen source, block its route or protect susceptible people. Hygiene, ventilation, safe water, vector control, vaccination and responsible behaviour are examples. Good answers link each measure to a specific transmission route.
Practical or data skill
Use outbreak scenarios to identify the likely route of transmission and propose a targeted control. Explain why a control useful for one disease may not work for another.
Examination tip
Name the route first, then explain how the proposed control interrupts it.
Review questions and suggested answers
Question 1
Define pathogen.
Suggested answer
A disease-causing organism.
Question 2
Give one direct and one indirect route.
Suggested answer
For example, blood contact and contaminated water.
Question 3
How does mucus protect the respiratory system?
Suggested answer
It traps particles and pathogens so cilia can move them away.
