S4.4.6 Chapter 6

Malaria, HIV and tuberculosis

How can we stop malaria, HIV and tuberculosis from spreading?

Your guess

Pick one before you read on. It is fine to be wrong.

Your guess

A All three spread through the air, so a mask stops all of them.
You picked A. Read on. At the end, the chapter comes back to your guess.
B All three spread by touch, so staying away from ill people stops them.
You picked B. Read on. At the end, the chapter comes back to your guess.
C They cannot be stopped. Luck decides who gets them.
You picked C. Read on. At the end, the chapter comes back to your guess.
D Each spreads in its own way, so each is stopped in its own way.
You picked D. Read on. At the end, the chapter comes back to your guess.

By the end you can

Describe how malaria spreads and how to prevent it
Explain how HIV spreads and how treatment helps
Explain how tuberculosis spreads and is treated

Three diseases affect millions of people. Each is caused by a different kind of pathogen and spreads in a different way. So each is stopped in a different way. This chapter takes them one at a time. Where a person may be ill, the advice is the same: see a health worker.

Three diseases and how each mainly spreads. Malaria is caused by a protist, HIV by a virus and tuberculosis by a bacterium.

Malaria is caused by a parasite, which is an organism that lives in or on another organism and harms it. The parasite is a protist. It is carried by female Anopheles mosquitoes, which live in warm places. A female needs blood to make her eggs, so she bites people.

The malaria cycle. The parasite lives in people and in mosquitoes, and the mosquito carries it between people.

The cycle goes round and round. The parasites first multiply in the liver. Then they infect red blood cells, multiply inside them and burst them. This releases more parasites, and the person has a fever and chills. A mosquito that bites an infected person takes up parasites, and passes them on with its next bite.

Malaria is not spread by air, by touch or by sharing food. Almost always it needs the mosquito. Very rarely it passes in blood, for example from a mother to her baby or in a transfusion. So prevention is aimed at the mosquito. Sleeping under a bed net stops bites at night, when many of these mosquitoes bite. Many nets are treated to kill mosquitoes that land on them.

Mosquitoes lay their eggs in still water, so getting rid of standing water means fewer mosquitoes. A repellent on skin and clothes keeps mosquitoes from biting, and covering arms and legs from dusk to dawn also helps. Vaccines against malaria now exist, but they give only partial protection. Nets and the other steps still matter.

Households in one village, with and without a bed net. Each line is 30 households. Example numbers.

Worked example

A village has 120 households. The bar chart shows how many have a bed net. What percentage of the households have a net? The numbers are an example.

Households with a net: 90. Households in all: 120.
Percentage = 90 ÷ 120 × 100 = 75.

Answer: 75%

A person in a place with malaria who has a fever should see a health worker quickly. Malaria can be tested for and treated, and it can become severe fast if it is not treated. Young children and pregnant women are at higher risk, so they need care sooner.

Try it

Find the standing water

You need: a pencil and a sheet of paper, an adult to walk round with you.

Be safe: Do not climb to reach a roof or a gutter. Ask an adult. Do not use a chemical to clean the places.

Walk round your home and the yard with an adult. Look for places where water can stand for days. Examples are buckets, old tins and saucers under plants.
Write down each place you find.
Next to each one, write what to do: turn it over, empty it, or cover it. A water store that is needed should have a tight cover.
Look again after a week and empty the places that filled up.

What you will see: You will find more places than you expect. A mosquito needs only a small amount of still water to lay eggs. Emptying a place at least once a week breaks the cycle, because the young need days in the water to grow.

If you cannot try it, this is what happens.

HIV is a virus. Its full name is Human Immunodeficiency Virus. It attacks a kind of white blood cell that helps to run the body's defences. Over time, if it is not treated, the defences weaken, until the body cannot fight infections that it normally fights off. This late stage is called AIDS.

HIV is in the blood and in some other body fluids of a person who has it. It passes only when these fluids get into another person's body. This can happen in four main ways. Blood from an infected person can get into a cut or onto a shared needle. It can pass during sex without a condom. It can pass from a mother to her baby in pregnancy, at birth or in breast milk. And it can pass through blood that was not tested before a transfusion.

HIV does not spread by touch, hugs, handshakes, sharing food or cups, coughing, toilets or insects. You cannot catch it from living or working with a person who has it. A mosquito that bites an infected person does not pass HIV on. There is no reason to avoid anyone who has HIV, and every person should be treated with respect.

Which kinds of contact spread HIV, and which do not. Clean needles, tested blood, condoms and treatment each cut one of the ways it spreads.

There are ways to prevent it. Never share needles. Use only blood that has been tested. A condom used correctly every time is very effective at stopping HIV passing during sex. A pregnant woman with HIV can be treated, which greatly lowers the chance of passing it to her baby.

The only way to know whether a person has HIV is a test. A health worker can test a small sample of blood or saliva. A test taken soon after HIV gets in may not find it yet. A health worker may ask for a second test some weeks later. Testing should be private, and a health worker explains the result. If the result is positive, treatment can start at once.

Draw it first

How treatment helps

1 A test shows that a person has HIV. A health worker gives treatment, which is a combination of medicines taken as the health worker directs.
2 The medicines keep the amount of virus in the blood very low. The white blood cells are not destroyed, so the defences stay strong.
3 The person stays healthy and lives a long life. Taken as directed, treatment can lower the virus until a test cannot find it. Then HIV does not pass to a sexual partner.

There is no cure for HIV yet, and no vaccine. Treatment does not remove the virus, so it must be kept up for life, as the health worker directs. Scientists are still searching for a cure.

Tuberculosis is caused by a bacterium. It mostly affects the lungs, but it can affect other parts of the body. It spreads through the air. When a person with tuberculosis in the lungs coughs, tiny droplets with the bacterium enter the air. Others breathe them in. It spreads most in crowded, closed rooms with little fresh air.

Tuberculosis spreads as droplets in the air. Fresh air and covered coughs cut this route.

Tuberculosis does not spread by touch or by sharing dishes. Many people who breathe in the bacterium do not become ill, because their white blood cells hold it in check. While it is held in check, they cannot pass it on. The bacteria can stay asleep in the body for years, then wake up. This is most likely when the defences weaken, for example in a person with HIV who has no treatment. In others the bacteria multiply, and the person has a cough that lasts for weeks, a fever, night sweats and weight loss.

A person with a cough that lasts for weeks should see a health worker. The health worker can test for tuberculosis, with tests on what is coughed up and an X-ray picture of the lungs. Tuberculosis is treated with a long course of antibiotics from a health worker. The course lasts several months, often six, and longer when the bacteria are resistant.

The course is long because the bacteria divide slowly and hide inside cells. Several antibiotics are used together. People feel better after a few weeks, but the bacteria are not all dead yet. The course must be taken to the end. Stopping early can leave bacteria alive, and the ones left are the most likely to be resistant. That makes the disease much harder to treat. After the first weeks of treatment, a person is much less likely to pass it on.

Worked example

A town of 24 000 people had 36 cases of tuberculosis in a year. How many cases is that for every 100 000 people? The numbers are an example.

There were 36 cases among 24 000 people.
Divide the cases by the people: 36 ÷ 24 000 = 0.0015.
Multiply by 100 000: 0.0015 × 100 000 = 150.

Answer: 150 cases

A wrong idea many people have

You can catch HIV by sharing a cup, a toilet or a hug with a person who has it.

Why it feels right: HIV is a serious disease, and many diseases do spread through the air, through touch or through shared things.

The test that breaks it: HIV passes only when infected blood or certain body fluids get into another person's body. Millions of people live, work and eat with a person who has HIV, and do not become infected.

What is true: HIV does not spread by touch, hugs, cups, food, toilets, coughing or insects. A person with HIV needs respect, not distance.

Where to get help. A health worker can test for malaria, HIV and tuberculosis, and treat all three. Testing should be private. If you think you have been exposed to HIV, see a health worker as soon as possible, within three days. Medicine to prevent HIV must start in that time. See a health worker quickly for a fever in a malaria area, and for a cough that lasts for weeks. Nobody may touch you without your yes. If someone does, or if you are afraid, tell an adult you trust or a health worker as soon as you can. It is not your fault.

Key words

malaria: a disease caused by a protist that female Anopheles mosquitoes carry from person to person.
parasite: an organism that lives in or on another organism and harms it.
repellent: something put on skin or clothes that keeps mosquitoes from biting.
HIV: a virus that attacks white blood cells and weakens the body's defences.
test: a way for a health worker to find out whether a person has a disease.
tuberculosis: a disease caused by a bacterium, usually in the lungs, that spreads in droplets from a cough.

Back to your guess

The answer is D: Each spreads in its own way, so each is stopped in its own way.

Malaria is spread by mosquito bites, HIV by blood and some body fluids, and tuberculosis by coughs. Each has its own ways to stop it, and each can be tested for and treated by a health worker.

Keep it

Copy this into your exercise book.

Malaria: a protist, carried by female mosquitoes. HIV: a virus, passed by blood and some body fluids, never by touch. Tuberculosis: a bacterium, spread by coughs. Each can be tested for and treated by a health worker.

Draw: Three boxes: a mosquito for malaria, a drop of blood for HIV and a cough for tuberculosis. Write one way to stop each.