3.4 Diseases: Causes & Types
A disease is a condition that affects the normal working of the body or mind — it happens when one or more organs or organ systems stop functioning properly. Diseases come from very different causes, and sorting them out is the first step to preventing them.
Two big families of disease
Communicable vs Non-communicable
- Communicable (infectious) diseases are caused by pathogens — disease-causing germs such as bacteria, viruses, fungi, protozoa, or worms — and can spread from one person to another. Examples: common cold, typhoid, malaria, chickenpox.
- Non-communicable diseases do not spread between people. They are linked to lifestyle, diet and environment. Examples: diabetes, heart disease, cancer, asthma.
Sort these diseases into the two families below.
How communicable diseases spread
Pathogens travel by a few main routes. Some pathogens are carried by insects such as mosquitoes and houseflies — these carriers are called vectors.
| Spreads through | Disease | Pathogen | Prevention |
|---|---|---|---|
| Air | Common cold, influenza | Virus | Wash hands, don’t share items, cover mouth/nose, mask |
| Air | Chickenpox, measles | Virus | Isolate patient, hygiene, vaccination |
| Air | Tuberculosis (TB) | Bacteria | Avoid close contact, hygiene, vaccination |
| Water/food | Cholera, typhoid | Bacteria | Boiled water, cooked food, sanitation, vaccination |
| Water/food | Hepatitis A | Virus | Boiled water, vaccination |
| Water/food | Ascariasis | Worms | Clean food & water, good sanitation |
| Insect (vector) | Malaria | Protozoa | Mosquito nets & repellents, control breeding |
| Insect (vector) | Dengue | Virus | Nets & repellents, remove still water |
Simple Habits That Stop the Spread Wash hands with soap; cover your mouth and nose when coughing or sneezing; wear a mask in crowds; don’t share towels or handkerchiefs; keep home, food and water clean; and stay home and rest when unwell — it helps you recover and protects everyone around you.
Some worms (like roundworms) live as parasites inside the digestive system, feeding on our nutrients. A parasite is an organism that lives in or on another living being. These worms usually spread through contaminated food, water or soil.
Non-communicable diseases
Non-communicable diseases — cancer, diabetes, heart disease, asthma — are now the most common cause of death in India. They come from lifestyle, diet and environment, not germs. Some are deficiency diseases (like scurvy, anaemia, goitre) caused by a lack of specific nutrients in the diet. Many last a long time (more than three months) and are called chronic diseases.
The Diabetes Surge Diabetes is becoming more common in adults and children — India now has one of the highest numbers of people with diabetes in the world. It develops from a mix of hormonal imbalance, unhealthy eating, lack of activity, and being overweight. The good news: healthy habits can often prevent or manage it.
Be a Scientist: Kamal Ranadive Kamal Ranadive (1917–2001) was a pioneering Indian biomedical researcher. She studied how hormones and certain viruses are linked to cancer, improving its prevention and treatment, and showed how tobacco, diet and pollution raise cancer risk — underlining how much a healthy lifestyle matters.