Compare transmission routes
Explain how cholera, malaria, tuberculosis and HIV can pass between hosts.
Cambridge International AS & A Level Biology 9700, 2028–2030 syllabus, Version 1. Educational biology content only: it does not diagnose illness or replace advice from a qualified health professional.
Before you begin
- A pathogen is a disease-causing microorganism or infectious agent; transmission describes how it passes between hosts.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which type of transmission is associated with cholera?
What you will learn
- Explain the main transmission route for each named disease
- Distinguish water-borne, vector-borne, airborne and body-fluid transmission
Build the explanation
Cholera spreads when food or water is contaminated with Vibrio cholerae, often where sanitation is inadequate. Malaria is transmitted when an infected female Anopheles mosquito introduces Plasmodium parasites during a bite; the mosquito is a vector. Pulmonary TB can spread through infectious particles in the air released by a person with active disease when coughing, sneezing or speaking. HIV can be transmitted through infected blood, semen, vaginal fluids or breast milk, including from parent to child. The routes are biologically different.
Apply it carefully
Use the disease name, source and route in one causal chain. A vector carries a pathogen between hosts; contaminated water is an indirect environmental vehicle; TB is airborne; HIV is not spread by ordinary sharing of food, hugs or handshakes. Avoid adding malaria life-cycle stages: they are not required for this syllabus outcome.
Pause and explain
Which route is associated with pulmonary TB?
Worked example
How can a mosquito transmit malaria between people?
Show the worked solution
- Name the vector.
- An infected female Anopheles mosquito passes Plasmodium during a bite.
Answer Malaria is transmitted by the bite of an infected female Anopheles mosquito, which acts as a vector for Plasmodium.
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Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Match each disease to a route: cholera, malaria, TB and HIV.
Give me a hint
Identify the contaminated vehicle, vector, air route or body fluid.
Compare my reasoning
- Cholera: contaminated food/water; malaria: infected female Anopheles vector.
- TB: airborne particles; HIV: infected blood, sexual fluids or breast milk.
Cholera: ingestion of food or water contaminated with V. cholerae. Malaria: bite from an infected female Anopheles mosquito. TB: inhalation of infectious airborne particles from active disease. HIV: contact with infected blood, semen, vaginal fluids or breast milk, including parent-to-child transmission.
Look for these in your work
- All four routes distinguished
- Vector named
- HIV body-fluid route named
A learner believes malaria passes mainly through casual contact with an infected person. Correct the claim.
Give me a hint
Distinguish direct contact from the biological vector.
Compare my reasoning
- Malaria is not spread by ordinary casual contact.
- The main route is an infected female Anopheles mosquito bite.
Malaria is not transmitted by ordinary casual contact; it is transmitted mainly through the bite of an infected female Anopheles mosquito, which carries Plasmodium.
Look for these in your work
- Casual-contact claim corrected
- Vector and agent identified
A community reduces water contamination but sees no change in malaria transmission. Explain why the control may not target the malaria route.
Give me a hint
Compare the pathogen's route with the intervention.
Compare my reasoning
- Safe water targets water-borne transmission such as cholera.
- Malaria is transmitted by a mosquito vector, so vector exposure must be addressed.
Improving safe water can reduce diseases spread through contaminated water, such as cholera. Malaria is vector-borne, so reducing contact with infected female Anopheles mosquitoes and controlling the vector are more directly relevant; the route-specific intervention differs.
Look for these in your work
- Water intervention route identified
- Malaria vector route identified
- Control matched to transmission
Common mistakes
- Calling a mosquito a pathogen rather than a vector
- Claiming HIV spreads by ordinary social contact
- Applying water treatment as the direct malaria-control route
What can you explain now?
Which type of transmission is associated with cholera?
Compare with the explanation
Ingestion of contaminated food or water
Vibrio cholerae can spread through contaminated food or water.
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Make it stick
What is the source and route of transmission for cholera, malaria, TB and HIV?
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.