Year 9 Science · Unit 1 · Lesson 3

Disease Transmission

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Learning Goals

Identify the transmission route of a disease from a real-world scenario and justify the classification.
Apply knowledge of the chain of infection to select appropriate prevention strategies.
Explain why different transmission routes require different control measures.

Warm Up

Because… chain

Fill in the missing effects. Each cause leads to the next step in how a foodborne disease spreads, and how it can be stopped.

A food worker does not wash their hands after using the bathroom, then handles salad ingredients

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Salmonella bacteria are now present on the salad, which is served at room temperature

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Customers eat the contaminated salad and ingest the bacteria

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Health authorities identify the source and order the restaurant to close and deep-clean

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Which link in the chain of infection was broken by closing the restaurant?

Your Turn

Real-world context

In March 2024, a student at a Sydney secondary school was diagnosed with typhoid fever after returning from travelling in South Asia. NSW Health was notified. Typhoid is caused by the bacterium Salmonella typhi and results in high fever, abdominal pain, and can be fatal without treatment. In 2023, 50 cases of typhoid were reported in NSW, most linked to overseas travel or contact with travellers. The primary transmission route is faecal-oral contamination of food and water.

(a) Identify the transmission route for typhoid fever and explain the specific mechanism by which a person in Australia could become infected if they had not travelled overseas.

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(b) As a public health officer, describe two immediate measures you would implement at the school, and explain which specific link in the chain of infection each measure targets.

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Show What You Know

1. Compare how the control strategies for an airborne disease like tuberculosis differ from those for a vector-borne disease like malaria. Refer to the specific transmission route for each disease in your answer.

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2. Australia eliminated rubella in 2018. Explain how vaccinating more than 95% of the population could stop an airborne disease from spreading, even though vaccination does not directly kill the pathogen.

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Wrap Up

In one sentence, what was the main idea of this lesson?