The shape of the lesson
By the end of the lesson, learners can
- Run an outbreak: Choose a disease, leave every box unticked and press Run the outbreak: one infected person enters a community of 200.
- Biological, social, economic: Exam questions ask you to discuss the factors.
- Why some diseases are harder to stop: Smallpox was eradicated by vaccination.
- Point of attack: treat the infected, block the route or protect the host.
- Biological: resistance, hiding in cells, changing antigens, carriers, vectors.
- Social: crowding, disasters, stigma, behaviour, access to clinics.
- Economic: cost of infrastructure, drugs and long treatment in poor countries.
One picture every idea returns to
Control measures break the chain of transmission at one of three points: treating infected people so they stop passing the pathogen on, blocking the route (clean water, mosquito nets, condoms) or protecting the next host (vaccination). Each one is limited by biological factors (drug and insecticide resistance, pathogens hiding inside cells, many strains or changing antigens, symptomless carriers, no vaccine for HIV), social factors (crowding in refugee camps and cities, natural disasters and war, stigma, whether people use nets or condoms or finish treatment) and economic factors (the cost of sewage systems, drugs, nets and long courses of treatment, often in the poorest countries). Details of the malaria life cycle are not needed.
Forty-five minutes, phase by phase
| Time | Phase | What happens in the room | Grouping |
|---|---|---|---|
| 0 to 5 min | Hook: predict | Open with the question in the title, Breaking the chain is biology, people and money.. Each disease can be attacked at three points: the infected person, the route and the next host. Put the figure on the board: it is the one picture every idea in the lesson returns to. | Whole class, then pairs |
| 5 to 13 min | Teach and check: Run an outbreak | Choose a disease, leave every box unticked and press Run the outbreak: one infected person enters a community of 200. Project tab 3 of the lab (Infectious diseases lab, prevention and control) and let a student drive it while the class predicts. | Whole class, then pairs |
| 13 to 21 min | Teach and check: Biological, social, economic | Exam questions ask you to discuss the factors. | Pairs |
| 21 to 30 min | Teach and check: Why some diseases are harder to stop | Smallpox was eradicated by vaccination. | Corners |
| 30 to 36 min | Check | The four Stage 1 questions from the student lesson, answered on mini whiteboards or by show of fingers. Re-teach the one most get wrong. | Individual, then whole class |
| 36 to 43 min | Plenary | The exam-style questions from Stage 2, one at a time: thirty seconds alone, then a random call. The feedback lines in the key give the examiner's wording. | Individual, random call |
| 43 to 45 min | Exit and homework | Set the worksheet below (6 questions, 20 marks). Learners self-assess against the objectives before they leave. | Individual |
Protect the parts that carry the learning
The sequence carries about fifty minutes of material, so the lab is driven by one student while the class predicts rather than explored freely. Times are a guide.
Protected: the check at 30 minutes. It is the only individual read on whether the key idea landed, and it is not cut.
Cut first if the build overruns: the last check in Why some diseases are harder to stop, never the check or the plenary.
In a 60 minute block: run worksheet questions 1 to 3 in class as a Rally Coach set and model both the hardest worked example and its check live.
Corners
Put one answer or viewpoint in each corner of the room. Students move to the corner they agree with, justify the choice to a partner there, then hear one voice from each corner before the reveal.
The full structure, with its variations and the other twelve, is on the cooperative-learning page.
What to head off, and how
| Trap learners fall into | Teaching move that pre-empts it |
|---|---|
| A treatment that saves lives does not always reduce transmission. | Oral rehydration solution prevents death from dehydration in cholera, but the patient still releases bacteria in faeces. In the model the curves do not change when only that box is ticked. |
| Do not just list measures. | A discuss question needs the factor and its effect: for example, mosquitoes have become resistant to insecticides so spraying kills fewer of them and the vector survives to transmit Plasmodium. |
Preventing and controlling infectious diseases: worksheet
6 questions, 20 marks. Written in the style of the papers; no past paper question is reproduced.
State three ways of reducing the transmission of cholera.
Explain why it has proved very difficult to eradicate malaria.
Suggest why the control of TB in a country is harder when a large proportion of the population is infected with HIV.
Discuss the social and economic factors that need to be considered in the control of HIV/AIDS.
State what is meant by DOTS in the treatment of TB and give one reason for using it.
In the lab's outbreak model for malaria, ticking insecticide-treated bed nets alone gives a smaller outbreak, and ticking bed nets together with antimalarial drugs stops the outbreak almost at once. Explain why the combination is more effective than either measure alone.
Answer key and marking notes
- Treat sewage so that faeces do not contaminate water supplies.
- Provide clean, piped or chlorinated (or boiled) drinking water.
- Hygiene: hand washing, and washing or cooking food in clean water; (also: oral vaccination).
- Plasmodium has become resistant to many antimalarial drugs (such as chloroquine).
- Anopheles mosquitoes have become resistant to insecticides.
- The parasite spends time inside liver cells and red blood cells and changes its antigens, so the immune system and vaccines are only partly effective.
- Mosquitoes breed in any small area of standing water, and many affected countries cannot afford large control programmes; people may not use nets consistently.
- HIV destroys T-helper cells, so the immune system is weakened.
- People with HIV are more likely to be infected with TB and to develop active TB.
- More people with active TB means more bacteria released in droplets, so more transmission.
- Treating patients for both diseases at once is more complex and costly.
- Social: stigma may stop people being tested or telling partners, so they continue to transmit HIV unknowingly.
- Social: cultural or religious attitudes may reduce condom use; education campaigns are needed.
- Economic: antiretroviral drugs must be taken for life and are expensive for poor countries (though costs have fallen).
- Economic: illness and death of working-age adults reduces income, leaves orphans and harms the national economy.
- Directly observed treatment, short course: a health worker watches the patient take each dose of the drugs.
- It makes sure the whole course is completed, so the infection is cured and drug-resistant strains are less likely to develop.
- Bed nets reduce the number of bites, so fewer new people are infected by each infected person.
- Antimalarial drugs cure infected people sooner, so each person is infectious to mosquitoes for a shorter time.
- Together the average number of new cases per infected person falls below one, so the outbreak dies out.
8 multiple-choice questions on this lesson
From the topic question bank. Assign them in the app for a marked score in your gradebook, or run the topic as a class game.
Which measure against TB works by protecting people before they are exposed to the bacteria?
- ABCG vaccination
- Bcontact tracing
- CDOTS treatment
- Dtesting sputum samples
Which is an economic factor that affects the control of malaria?
- Agovernments in many affected countries cannot afford large spraying programmes
- BAnopheles mosquitoes have become resistant to several insecticides
- Csome families do not sleep under their bed nets every night
- DPlasmodium changes its surface antigens inside the human host
Draining ponds and removing old containers that collect rainwater reduces the number of malaria cases in a village. Why?
- Amosquito larvae need standing water to develop, so fewer adult vectors are produced
- BPlasmodium is carried in standing water and is drunk by villagers
- Cstanding water releases droplets that carry Plasmodium into the air
- Dthe water dilutes the insecticide on the bed nets that people use
During a cholera outbreak, people are advised to boil their drinking water or add chlorine tablets to it. How does this reduce transmission?
- Ait kills Vibrio cholerae in the water before the water is swallowed
- Bit makes people immune to Vibrio cholerae for several years
- Cit removes the toxin from the small intestine of infected people
- Dit replaces the water and ions lost by people who have diarrhoea
Which is a biological factor that makes TB difficult to treat?
- Athe bacteria can survive inside phagocytes and grow slowly, so treatment lasts months
- Bpeople living in crowded housing pass the bacteria on to each other
- Cpatients may feel ashamed and avoid being tested for the disease
- Dthe drugs and supervision for a long course of treatment are costly
The graph shows malaria cases in a region. Insecticide-treated bed nets were issued to every household in year 3. Which is the most likely explanation for the rise in cases from year 7?
- Amosquitoes resistant to the insecticide on the nets became more common
- BPlasmodium in the mosquitoes became resistant to the insecticide
- Cpeople in the region became immune to Plasmodium after year 7
- Dthe nets made the mosquitoes lay more eggs in standing water
Without treatment, about 25% of babies born to mothers with HIV become infected. With antiretroviral drugs for the mother and baby, this falls to about 2%. What is the percentage reduction in the risk of transmission?
- A92%
- B23%
- C8%
- D1150%
Health workers argue that testing people for HIV and giving antiretroviral drugs to everyone who is positive helps to prevent new infections, not just to treat the people who take them. Which is the best explanation?
- Athe drugs keep the amount of virus in body fluids very low, so the person is far less likely to pass it on
- Bthe drugs act as a vaccine, so sexual partners of the person become immune to HIV
- Cthe drugs kill every virus particle in the body, so the person is permanently cured
- Dthe drugs destroy T-helper cells, so the virus has no cells left to infect
Quiz key
The BCG vaccine is given to people, often babies, who are not infected, so that their immune system is primed before any exposure. Contact tracing finds people who may already have been infected by a known case. DOTS is supervised treatment of people who already have TB. Testing sputum diagnoses people who are already ill.
The cost of insecticide, staff and equipment for spraying is an economic factor, and many of the countries worst affected by malaria have low incomes. Insecticide resistance in mosquitoes is a biological factor. Whether people use their nets is a social factor about behaviour. Antigen change in Plasmodium is a biological factor that limits vaccines and immunity.
Female Anopheles lay eggs in standing water, where the larvae and pupae develop. Removing breeding sites means fewer adult mosquitoes to carry Plasmodium between people. Malaria is not caught by drinking water; that is how cholera spreads. Malaria is not airborne; airborne droplets spread TB. Standing water has nothing to do with the insecticide on nets.
Boiling and chlorine kill the bacteria in the water, breaking the faecal-oral route at the point where contaminated water would be swallowed. They do not give immunity; only infection or a vaccine does that. They act on water outside the body, not on toxin already in the intestine. Replacing water and ions is what oral rehydration solution does: it treats the patient but does not stop transmission.
Mycobacterium grows slowly and can survive inside macrophages, out of reach of many drugs and of antibodies, so several antibiotics are needed for at least six months; that is a biological factor. Crowded housing and stigma about testing are social factors. The cost of drugs and supervised treatment is an economic factor.
The insecticide kills mosquitoes, so it is a selection pressure on the vector: mosquitoes with resistance survive, breed and become common, the nets protect less, and cases rise again (nets wearing out would add to this). The insecticide does not act on Plasmodium, so the parasite does not become resistant to it. If people had become immune, cases would fall, not rise. Nets reduce bites; there is no reason they would increase egg laying.
Reduction = (25 − 2) ÷ 25 × 100 = 92%. 23 is the fall in percentage points, not the percentage reduction. 8% is the new risk as a percentage of the old one (2 ÷ 25 × 100). 1150% divides the fall by the new value instead of the original value.
Antiretroviral drugs inhibit HIV replication (for example by inhibiting reverse transcriptase), so the viral load in blood, semen and other fluids falls very low and transmission becomes much less likely. They are not vaccines and give partners no immunity. They do not cure HIV: the virus remains in infected cells, which is why the drugs are taken for life. They protect T-helper cells; destroying them is what HIV itself does.
What to project
The student lesson embeds these tabs. Open them full screen on the projector; every slider has a drag handle on the stage.
Slides for this lesson
A projectable deck for every pack is on the way. Until then, present the student lesson full screen: its sections, figure and lab tabs follow the same order as the plan above.