Lesson 1 of 5 / Infectious diseases in humans
Pathogen, disease and route
What is passed on when an infectious disease spreads?
In this lesson: Distinguish infectious from non-infectious disease and identify routes of pathogen transmission.
About 5 min
The key ideaAn infectious disease is caused by a transmissible pathogen. The pathogen, disease and transmission route are different parts of the explanation.
A waterborne pathogen can enter through ingestion. Safe water interrupts this route before it reaches the new host.
Boxes separate the pathogen source, transfer route and entry. The cross marks a route being reduced, not guaranteed zero transmission.
Explanation
A pathogen is a disease-causing organism or agent, such as a pathogenic bacterium or a virus. An infectious disease can be transmitted between people, directly or through a route such as contaminated food or water. A non-infectious disease is not passed between people in this way.
Influenza and pneumococcal disease are infectious. Type 2 diabetes and coronary heart disease are non-infectious: ordinary contact with an affected person does not transmit them. Non-infectious does not mean harmless, and exposure to an infectious pathogen does not mean every contact causes disease.
Different pathogens use different routes. Pathogens in contaminated food or drinking water can enter through the digestive system. Some are transmitted through particular body fluids, for example infected blood. Respiratory secretions and particles can carry respiratory pathogens between people.
Keep a causal chain clear: source of pathogen -> route of transfer -> entry into a new host. The disease name describes the resulting condition, while signs and symptoms are effects on the person. A cough may help disperse a respiratory pathogen, but a cough itself is not the pathogen.
Step by step
- 1
Name the cause
Identify the pathogen rather than naming only a symptom.
- 2
Trace the route
Use body fluids, contaminated food/water or respiratory particles as appropriate.
- 3
Identify the new host
Explain how the pathogen enters, then choose a measure that interrupts that route.
Worked example
Contaminated drinking water
A teaching case describes pathogenic bacteria entering drinking water and causing intestinal disease. Identify the pathogen and route.
One way to explain it
The pathogen is the disease-causing bacterium. The route is ingestion of contaminated drinking water, which carries the bacteria into the digestive system.
Why this answer works
- The bacterium is the cause, not the water itself.
- Water is the vehicle of transmission.
- State how the pathogen enters the new host.
Is this true? "Any illness shared by family members must be infectious."
Family members can share genes and environments as well as exposure to pathogens. Similar illness alone does not establish person-to-person transmission.