Stopping Your Medicine Early Can Make the Germs Stronger

Because feeling better means most of the bacteria are dead — not all of them. The ones still alive are the toughest, and stopping early leaves exactly those to multiply.

That is how antibiotic resistance builds, and it is the most important idea in this chapter. This page covers everything in the CBSE Class 8 Science chapter's second part: communicable and non-communicable diseases, how germs spread, lifestyle diseases, and vaccination and antibiotics.

Communicable (infectious) diseases are caused by germs and spread from person to person. Non-communicable diseases do not spread; they arise from within the body, from lifestyle, or from a deficiency.

Communicable, with the causative agent:

- Bacteria — typhoid, tuberculosis, cholera, tetanus, whooping cough
- Viruses — common cold, influenza, measles, chickenpox, dengue, hepatitis, polio
- Protozoa — malaria, amoebic dysentery
- Fungi — ringworm, athlete's foot
- Worms — tapeworm and roundworm infections

Non-communicable, with the underlying cause:

- Diabetes — the body cannot control blood sugar properly
- Obesity — more energy taken in than used up
- High blood pressure and heart disease — lifestyle and diet
- Cancer — uncontrolled growth of body cells
- Anaemia — iron deficiency; scurvy — vitamin C deficiency; rickets — vitamin D deficiency
- Asthma and allergies — an over-sensitive response of the body

So sitting beside a classmate with diabetes carries no risk at all, while sitting beside one with measles does.

The test is whether a germ is involved. A deficiency disease such as scurvy has a definite cause and definite symptoms but no germ, so it cannot be caught — and no amount of hygiene will prevent it. Only the right food will.

Along five routes, and each has its own preventive measure.

- Air — germs travel in the tiny droplets released when an infected person coughs or sneezes, and are breathed in by others. Examples: common cold, influenza, tuberculosis, measles. Prevented by covering the mouth when coughing and keeping rooms ventilated.
- Water — germs in contaminated drinking water. Examples: cholera, typhoid, jaundice, diarrhoea. Prevented by boiling, filtering and covering water.
- Food — germs on food that is stale, uncovered or handled with dirty hands. Examples: food poisoning, amoebic dysentery, typhoid. Prevented by washing hands, covering food and eating it fresh.
- Contact — touching an infected person or their belongings, such as a shared towel or comb. Examples: ringworm, scabies, conjunctivitis. Prevented by not sharing personal items.
- Vectors — animals that carry germs without being ill themselves. The mosquito is the most important: Anopheles carries malaria, and Aedes carries dengue and chikungunya. Houseflies carry cholera and typhoid onto uncovered food. Prevented by nets, repellents, screens and by removing breeding sites.

Emptying coolers, flower pots and old tyres once a week during the monsoon is the single most effective step against mosquito-borne disease, because it removes the standing water the larvae need.

A vector is the part students describe loosely. The mosquito does not cause malaria — the protozoan Plasmodium does. The mosquito only carries and injects it, which is why controlling mosquitoes controls a disease they never suffer from.

Both are lifestyle diseases — conditions arising mainly from how a person eats, moves and rests rather than from any germ.

Obesity develops when the energy taken in as food regularly exceeds the energy used up in activity. The surplus is stored as fat. Its main contributors are:

- Frequent oily, fried and sugary food
- Sweetened drinks in place of water
- Very little physical activity, with long hours sitting
- Irregular meals and late-night eating

Diabetes occurs when the body cannot control the level of sugar (glucose) in the blood, because the hormone insulin is not produced in sufficient amount or does not work properly. Blood sugar then stays high. It brings excessive thirst, frequent urination, tiredness and slow healing of wounds, and it tends to run in families as well as being linked to being overweight and inactive.

These two are connected: being obese makes diabetes more likely, and both raise the risk of high blood pressure and heart disease.

Prevention is the same for all of them — a balanced diet low in fried and sugary food, daily exercise, adequate sleep, and avoiding tobacco and alcohol.

The word lifestyle should not be read as blame, and that is worth stating carefully. Family history, age and other factors also play a part, so a person can develop diabetes while living carefully. What lifestyle changes do is shift the risk, which is why they are worth making rather than being a guarantee either way.

They do completely different jobs. A vaccine prevents a disease before it happens; an antibiotic treats one that already has.

Vaccination. A vaccine contains dead or weakened germs, or parts of them, which cannot cause the disease. The body's immune system responds by producing antibodies against them, and it keeps a memory of how. If the real germ ever arrives, antibodies are made quickly and in quantity, so the person does not fall ill. This lasting protection is immunity.

Vaccines are given against polio, measles, tetanus, tuberculosis, hepatitis, diphtheria and whooping cough, which is why every child has an immunisation schedule from infancy.

Antibiotics. These are medicines that kill bacteria or stop them multiplying, and they are used for bacterial illnesses such as typhoid and tuberculosis.

Two limits must be stated:

- Antibiotics have no effect on viruses, so taking them for a common cold or influenza does nothing useful.
- They must be taken as the full prescribed course, at the right doses.

Antibiotic resistance is what happens when these rules are broken. An antibiotic kills the weaker bacteria first. Stopping the course early — or taking antibiotics without need — leaves the hardiest survivors alive, and they multiply into a population the medicine no longer harms. That illness then becomes far harder to treat, for the patient and for everyone they pass it to.

So the rules follow directly from the mechanism: complete every course, never take leftover antibiotics from an earlier illness, never share them, and never use them for a viral infection.