All of us fall ill from time to time. Sometimes we have a mild headache, sometimes a cold or a fever, and at other times a more serious disease. But what does it mean to be healthy? And what does it mean to be free from disease? Health is not merely the absence of disease; it is a state of complete physical, mental and social well-being.
Disease and health are closely connected to our surroundings, our habits, our nutrition and the community in which we live. A clean environment, good food, proper exercise and mental peace all contribute to good health. In this chapter we study the difference between health and disease, the causes of diseases, how diseases spread, and how we can prevent them.
Understanding why we fall ill helps us appreciate the importance of hygiene, vaccination, and a healthy lifestyle, both for ourselves and for the community.
Health is a state of complete physical, mental and social well-being. Health is affected by many factors: 1. Social factors: A person living in a clean, well-ventilated area with good food and water is healthier than a person living in a polluted or crowded area. 2. Physical factors: Genetic disorders, environmental pollution, and infections affect health. 3. Economic factors: A person who cannot afford adequate food or medical care may have poor health. 4. Community factors: The health of an individual depends on the health of the community; if diseases are common in a community, every individual is at risk.
Disease: A disease is a condition in which the normal functioning of the body or one of its parts is disturbed. Disease means "dis-ease" - a state of discomfort. A person suffering from a disease has symptoms like fever, headache, weakness or rashes.
Disease and its causes: Disease can be caused by internal or external factors. Internal factors are inherited (genetic) defects or malfunctioning of organs, such as high blood pressure or diabetes. External factors include lack of proper nutrition, contaminated food and water, harmful micro-organisms (pathogens), and physical or environmental factors.
Diseases can be classified on the basis of the duration of the illness.
Acute diseases: Diseases which last for a very short time are called acute diseases. For example, the common cold, cough, and a mild fever last for a few days. The effect of an acute disease is usually not long-lasting.
Chronic diseases: Diseases which last for a long time, even for years, are called chronic diseases. For example, diabetes, tuberculosis and kidney disease last for a long time. Chronic diseases have severe, long-term effects on health and cause persistent poor health, tiredness and weight loss.
On the basis of the cause, diseases are classified into infectious and non-infectious diseases.
Infectious (communicable) diseases: These diseases are caused by micro-organisms called pathogens, which can be transmitted from an infected person to a healthy person. Examples are the common cold, malaria, typhoid, cholera, tuberculosis and AIDS.
Non-infectious (non-communicable) diseases: These diseases are not caused by pathogens and cannot be transmitted from one person to another. They are caused by internal factors, nutritional deficiencies or lifestyle. Examples are diabetes, cancer, heart disease, hypertension and arthritis.
Pathogens: The micro-organisms that cause diseases are called pathogens. They include bacteria, viruses, protozoa, fungi and worms.
Viruses: Viruses are the smallest pathogens. They reproduce only inside the cells of the host. Diseases caused by viruses include the common cold, influenza, measles, AIDS and COVID-19.
Bacteria: Bacteria are single-celled micro-organisms. Diseases caused by bacteria include typhoid, cholera, tuberculosis, and tetanus.
Protozoa: Protozoa are single-celled organisms that cause malaria (Plasmodium), kala-azar and amoebic dysentery.
Fungi: Fungi cause diseases of the skin such as ringworm and infections of the nails.
Worms (helminths): Worms cause diseases like filariasis (elephantiasis), intestinal worm infections and taeniasis.
Infectious diseases spread from an infected person to a healthy person through various modes:
Direct transmission: The disease spreads by direct contact between an infected person and a healthy person. Skin diseases, sexually transmitted diseases and diseases spread by sharing objects like towels and utensils are examples. Air-borne diseases like the common cold and tuberculosis spread through the droplets released when an infected person coughs or sneezes.
Indirect transmission: - Through water and food: Diseases like cholera, typhoid and hepatitis A spread through contaminated water and food. This is called the faecal-oral route. - Through vectors: Vectors are organisms that carry and transmit the disease-causing pathogen. The female Anopheles mosquito transmits malaria, the female Aedes mosquito transmits dengue, and the female Culex mosquito transmits filariasis. - Through blood: Diseases like AIDS and hepatitis B can spread through contaminated blood and blood products, shared needles and syringes, and from an infected mother to her baby.
Organ-specific diseases: Different pathogens affect different organs. Typhoid affects the intestines, malaria affects the liver and red blood cells, tuberculosis affects the lungs, and jaundice affects the liver.
Diseases can be prevented by two main strategies:
General ways of prevention: Maintaining good hygiene - washing hands before eating, drinking clean boiled water, eating nutritious food, keeping the surroundings clean, and preventing the breeding of mosquitoes by not allowing stagnant water. These general measures prevent a wide range of diseases.
Specific ways of prevention: - Immunisation: Vaccination protects us from specific diseases by creating immunity. Vaccines contain dead or weakened pathogens which make our body produce antibodies. Vaccination against diseases like tuberculosis (BCG), polio, measles, hepatitis B and tetanus has saved millions of lives. - Antibiotics: Antibiotics are medicines that kill or stop the growth of bacteria and are used to treat bacterial diseases. However, antibiotics do not work against viral diseases.
The treatment of disease follows two main principles:
Reduce the effect of the disease: Medicines are given to relieve the symptoms such as fever, pain or cough, so that the patient feels better. For example, paracetamol reduces fever.
Kill the cause of the disease: Medicines are given that kill the pathogen causing the disease. Antibiotics kill bacteria, and antimalarial drugs kill the Plasmodium protozoan. If the cause is removed, the disease is cured.
The treatment of infectious diseases works best when the immune system of the body is strong. A balanced diet, rest and proper care help the body fight infections.
The immune system of the body fights against pathogens. White blood cells (WBCs) destroy pathogens. When the body is first exposed to a pathogen, it produces antibodies; on a second exposure, the body produces antibodies much faster. This is the basis of vaccination.
Prevention is always better than cure, because: 1. It avoids the suffering caused by the disease. 2. It avoids the cost of treatment. 3. Some diseases, if not treated in time, cause permanent damage to organs.
By maintaining cleanliness, eating a balanced diet, getting vaccinated and keeping our surroundings free of disease-causing agents, we can prevent many diseases.
| Type of Disease | Duration | Example |
|---|---|---|
| Acute | Short time | Common cold, mild fever |
| Chronic | Long time | Diabetes, tuberculosis |
| Pathogen | Disease Caused | Example |
|---|---|---|
| Virus | Common cold, AIDS, measles | Corona, HIV |
| Bacteria | Typhoid, cholera, TB | Vibrio cholerae |
| Protozoa | Malaria, kala-azar | Plasmodium |
| Fungus | Ringworm | - |
| Worm | Elephantiasis | Wuchereria |
| Mode of Transmission | Disease | Vector/Host |
|---|---|---|
| Air | Cold, TB | Droplets |
| Water/food | Cholera, typhoid | Contaminated water |
| Vector | Malaria, dengue | Female Anopheles/Aedes mosquito |
| Blood | AIDS, hepatitis B | Infected blood |
In this chapter we learned that health is a state of complete physical, mental and social well-being, and that disease is a disturbance in the normal functioning of the body. Diseases can be acute or chronic, and infectious or non-infectious. We studied the different pathogens - viruses, bacteria, protozoa, fungi and worms - and the diseases they cause, along with the various modes of transmission, including air, water, food, vectors and blood. We understood the importance of hygiene, safe drinking water, vaccination and the control of mosquito breeding in preventing diseases. Treatment follows two principles: relieving symptoms and eliminating the cause. The chapter reminds us that prevention is better than cure, and that a healthy individual depends on a healthy community.