Diseases: communicable and non-communicable

3.1 When the body is not working normally

A disease disturbs how the body or mind normally works. It arises when organs or organ systems stop doing their job. Some clear up quickly, while others linger for a long period and need regular treatment and care.

Diseases have different causes. Some are caused by germs such as bacteria, viruses, fungi, worms or protozoa. These disease-causing organisms are called pathogens. Others come from poor nutrition or unhealthy living. Understanding the cause matters, because prevention depends on it.

3.2 Symptoms and signs

When something goes wrong, the body gives signals. Some of these are felt by the person: pain, tiredness, dizziness. A sensation that the person feels is a symptom. Others can be seen or measured by another person: fever, rash, high blood pressure, swelling. These are signs. A doctor uses both kinds of information to work out what might be making a person unwell.

3.3 Communicable diseases

When pathogens cause an illness, it is a communicable disease, able to pass from one person to another. Typhoid, dengue, flu, chickenpox and COVID-19 are examples. Pathogens can enter the body through the air we breathe, through contaminated food or water, or through contact with an infected person.

Spread happens in several ways. One common route is the air, through droplets released when an infected person coughs or sneezes. Another is direct contact, such as shaking hands, or indirect contact through shared personal items such as towels and handkerchiefs. Some pathogens travel in contaminated drinking water or food. Insects such as mosquitoes and houseflies can also carry pathogens from one place to another; these insects are called vectors.

Worms can also cause infectious disease, living inside the body, especially in the digestive system. They live as parasites, feeding on nutrients from the host, and usually spread through contaminated food, water or soil, or through contact with infected people or animals.

Simple precautions work against many of them. Keep yourself and your surroundings clean. Wash hands with soap and water. Cover the mouth and nose while coughing or sneezing, and wear a mask in crowded places. Do not share towels or handkerchiefs. Keep home, food and water clean, and rest at home when unwell so that others are not infected.

3.4 Non-communicable diseases

Cancer, diabetes and asthma are not caused by pathogens and cannot pass between people. They relate to lifestyle, diet and surroundings, and many of them are chronic, lasting more than three months. Deficiency diseases such as scurvy, anaemia and goitre are also non-communicable; they result from a lack of particular nutrients in the diet.

Non-communicable diseases have become more common in India. Changes in lifestyle, including more processed food, less exercise and longer lives, are part of the reason. Non-communicable diseases now account for most deaths in India. Diabetes, for example, develops from a combination of hormonal imbalance, unhealthy eating habits, lack of physical activity and excess body weight.

3.5 Why the type of disease matters

Knowing whether a disease is communicable or non-communicable changes the way a person protects themselves. For a communicable disease, the defence is aimed at the pathogen and its route: clean hands, clean water, masks, mosquito nets, vaccination and staying away from others while unwell. For a non-communicable disease, the defence is aimed at long-term habits: a balanced diet, regular exercise, sleep, avoiding tobacco and regular health checks.

The two kinds also need different public responses. An outbreak of flu calls for quick action to break the chain of spread, while the rise of diabetes calls for long-term changes in food, activity and screening. Recognising the type helps a community choose the right tools instead of applying one solution everywhere.

The scientist Kamal Ranadive examined links between hormones, some viruses and cancer, and her studies connected tobacco, diet and pollution with higher cancer risk, one more reason a healthy lifestyle matters.

3.6 A closer look at diabetes

Diabetes deserves a closer look because it is becoming more common in adults and in children. India today counts among the countries with the most people living with diabetes. The disease often develops from a combination of hormonal imbalance, unhealthy eating habits, lack of physical activity and excess body weight.

Its warning signs include frequent urination, excessive thirst, weight loss, tiredness and wounds that heal slowly. A person with these signs should see a doctor rather than self-medicate. For people at risk, a balanced diet, regular exercise and a healthy weight reduce the chance of developing the disease, and early diagnosis helps keep it under control.

3.7 Investigating a disease

When a person feels unwell, the investigation follows a familiar pattern. The doctor listens to symptoms, looks for signs, and may order tests to confirm the cause. A cough and fever might point to a respiratory infection, while frequent thirst and urination might suggest diabetes. The same careful method used in a science experiment, collecting evidence before drawing a conclusion, applies to diagnosis.

The investigation also decides treatment. A bacterial infection may need an antibiotic, a viral infection usually does not, and a non-communicable disease may need long-term care rather than a single medicine. Treating every illness as if it were the same is one of the quickest ways to make health worse.