Health is defined as the state of complete physical, mental and social well-being.
The health of an individual is affected by changing internal and external factors including personal, economic, environmental and social factors.
Disease is the departure from normal health through a structural or functional disorder of the body.
Causes of Diseases
These are disease-causing factors that exist within the human body. Genetic disorders. Example: Haemophilia
These are disease-causing factors that enter the human body from outside and cause disease.
Disease-causing microorganisms. Example: Malaria
Levels of Immediate Causes
First-level cause: Primary cause/causative agent: Bacteria, virus Second-level cause: Secondary cause: Lack of good nourishment
Third-level cause: Tertiary cause: Poverty
Types of Diseases
Diseases in which the symptoms are quickly visible in the body and last for a shorter duration are called acute diseases. Examples: Common cold, malaria
Diseases which are long-term, with their symptoms lasting for months or years, are called chronic diseases. Examples: Elephantiasis, tuberculosis
Diseases which develop after birth are called acquired diseases.
Diseases caused by infectious agents or pathogens are called communicable or infectious diseases. Examples: Tuberculosis, chickenpox, measles
Diseases which do not spread from one person to another are called non-communicable or noninfectious diseases. Examples: Beriberi, scurvy, arthritis
Differences between Infectious and Non-infectious Diseases
1. Caused by attack of pathogens
1. Caused by factors other than pathogens
2. Caused by extrinsic factors
2. Caused by intrinsic factors
3. Transmitted from one person to another
3. Do not get transmitted from one person to another
4. Transmission of diseases occurs through direct contact or some medium
4. Transmission in hereditary diseases is from parent to offspring
5. Examples: Cholera, malaria
5. Examples: Diabetes, goitre
Means of Spread of Infectious Diseases
Spread through air when droplets of pathogens are expelled into the air because of coughing, sneezing or talking. Examples: Influenza, meningitis
Caused by consumption of contaminated water. Examples: Typhoid fever, cholera, hepatitis A
Caused by consumption of food contaminated with chemical toxins or pathogens. Examples: Taeniasis, trichinosis
Caused by pathogens transmitted by vectors such as insects and ticks. Examples: Malaria, elephantiasis
Sexually transmitted diseases
Caused by pathogens transmitted by sexual contact. Examples: AIDS, syphilis
Caused by pathogens present on inanimate objects such as clothing and bedding used by infected people. Examples: Scabies, ringworm
Organ-specific and Tissue-specific Manifestations of Diseases
The signs and symptoms of a disease depend on the tissue or organ which the microbe targets.
The severity of disease manifestation depends on the number of microbes within the body.
During infection, the immune system gets activated. It sends many soldier cells to the affected tissue to kill the microbes. This causes inflammation.
Inflammation is due to the escape of some chemicals which cause allergic reactions in our body. They attract blood supply because of which the amount of blood and the temperature of the surrounding area increase. The consequent swelling of the area is called oedema.
Plasma and white blood cells (WBCs) of the immune system of the body are discharged at the affected site. Plasma contains products such as antibodies and macrophages which kill or inhibit the growth of pathogens.
Doctors carry out confirmatory tests such as laboratory tests of blood, urine and stool or even perform an X-ray to confirm the presence of a disease.
Principles of Treatment of Diseases
Principles of Prevention of Diseases
Prevention of diseases follows three basic principles:
General Ways of Prevention of Infectious Diseases
We can prevent exposure to air-borne microbes by providing living conditions which are not overcrowded.
We can prevent exposure to water-borne microbes by providing safe, filtered and boiled drinking water.
We can provide clean environments to prevent exposure to vector-borne microbes. This would not allow their multiplication.
Specific Ways of Prevention of Infectious Diseases
Immunisation is the process by which an individual’s immune system is equipped to fight off infectious agents.
Vaccination provides active immunity.
Vaccines against some common diseases such as BCG vaccine, DPT vaccine, polio vaccine, vaccines for tetanus, diphtheria, whooping cough, measles and many others have been administered in India.