Treatment and prevention

Two ways to treat an illness

A child has a high fever and a cough. The doctor can do two different things.

1. Treat the symptoms. The symptoms are what the patient feels: fever, pain, cough. A medicine can bring the fever down, and rest and food help the body. This makes the patient feel better. It does not remove the microbe.
2. Treat the cause. A medicine can kill the microbe, or stop it from multiplying. This removes the cause of the disease.

Both matter. If we only treat the symptoms, the microbe keeps on damaging the organ. If we only kill the microbe, the patient may still be in pain while the body recovers. A good treatment uses rest and nourishing food to help the body, and a medicine for the cause when there is one.

Why antibiotics kill bacteria and not viruses

A medicine that kills microbes must harm the microbe without harming us. This is possible because the microbes do some things differently from our own cells.

Bacteria make their own materials and build a cell wall around themselves. Human cells have no cell wall. An antibiotic, such as penicillin, blocks the steps that build the wall of the bacterium. The bacterium cannot grow, and it dies. Our cells do not use these steps, so they are not harmed.

Viruses are different. They have none of these steps. A virus lives inside our cells and uses our cell machinery to make more viruses. So an antibiotic has nothing to act on. A person with a common cold or influenza gains nothing from antibiotics. The body fights these infections itself, with rest and plenty of fluids. Medicines against a few viruses do exist, but each acts against only one virus, and they are much harder to make than antibiotics.

Read the line at the foot of the picture. Antibiotics are for bacteria. Viruses, fungi, protozoa and worms need other kinds of medicine.

Finish the course

Suppose a patient with a bacterial infection takes the antibiotic for two days and feels better. The patient stops. Is it safe to stop?

No. In every large group of bacteria, a few may happen to survive the medicine. These are resistant bacteria. If the patient stops early, the weaker bacteria are dead but the resistant ones are left. They multiply, and the illness returns. This time the same antibiotic may fail. A bacterium that is resistant passes its resistance on to its offspring, and it can spread to other people.

This is called antibiotic resistance. It grows when antibiotics are taken without need, for a cold for example, or when a course is not finished. That is why a doctor tells you to finish the whole course, and why you should never take an antibiotic on your own. Tuberculosis needs about six months of medicine for this very reason.

Look at what happens in the model below. The curve shows the bacteria in a patient who takes the medicine day after day.

With a share of $0$ % resistant, the bacteria fall towards nothing as the days go by. With some resistant bacteria, the curve levels off at the height of the dashed line. That is the number of resistant bacteria. They will grow back once the medicine stops. Taking the medicine for longer cannot reach below that line, which is why a doctor may change the medicine.

Prevention is better than cure

Treatment comes after a person is ill. A better plan is to keep the person from falling ill at all. There are two sets of principles.

General ways keep the microbe away. They work against many diseases at once.

• Clean drinking water. Boil water or treat it with chlorine, and cover it. This stops cholera and typhoid fever.
• Clean food. Cover food, wash vegetables, and wash hands before eating. This keeps flies and dirty hands away.
• Clean surroundings. Waste and sewage should be removed and not left in the open, where flies breed.
• No stagnant water. Mosquitoes lay their eggs in standing water, in pots, coolers and puddles. Draining it stops malaria and dengue.
• Fresh air and space. Open windows and uncrowded rooms make it harder for air-borne infections such as tuberculosis and influenza to spread.
• Good food and rest. A well-fed body fights microbes better.

Specific ways make the body ready to fight one particular microbe. This is called immunisation, and it is the subject of the next lesson.

Try it in Python

The program follows the bacteria in a patient who takes an antibiotic, day by day. About $5$ % of the bacteria are resistant, so the medicine kills only half of the others each day.

You should see the first days bring a big fall, and then the number levels off near $40$ thousand. Those are the resistant bacteria. They are not touched by the medicine, so they stay, and they will multiply.

Practise with new numbers

Common mistakes

• Using antibiotics for a cold or influenza. Both are caused by viruses, which antibiotics do not harm.
• Stopping when the signs go. The resistant bacteria are left behind and return.
• Thinking that treating the symptoms cures the disease. It only helps the patient feel better.
• Thinking that one way of prevention suits all diseases. Clean water stops cholera. Draining pools stops malaria. Each general way blocks a particular route.
• Believing that resistance is in the patient. It is the bacteria that become resistant, not the person.

Remember these

• Treatment can ease the symptoms, or kill the microbe that is the cause.
• Antibiotics block steps that bacteria need, such as building the cell wall. They do not work on viruses.
• Finish the course. Stopping early lets resistant bacteria survive and multiply.
• General prevention keeps microbes away: clean water, food and surroundings, no stagnant water, fresh air.
• Specific prevention is immunisation.

Check yourself

Try each one on your own first. If you are stuck, open a hint. Then check with Show the answer.

1. What is the difference between treating the symptoms and treating the cause?

2. Why does an antibiotic work on bacteria but not on a virus?

3. A girl takes an antibiotic for $2$ days and then stops because she feels well. What may go wrong?

4. Name two general ways of preventing disease, and the disease each one helps to stop.

5. A patient has $400$ thousand bacteria, none resistant, and a medicine halves them each day. How many thousand are left after $2$ days?