Health is a state of complete physical, mental and social well-being. Itis notjust the absence of disease. Factors which affect health are genetic disorder, infections and lifestyle.

Any physical or functional change from the normal state that causes discomfort or disability or impairs the health of a living organism is called a disease.There are two types of diseases: Infectious and non-infectious.
Infectious diseases are caused by pathogens like virus, rickettsia, bacteria, fungi, protozoa and helminths. They are transmitted from infected to healthy person such as common cold, tuberculosis and AIDS. Non-infectious diseasesremain confined to the person affected and do not spread to others.The examples of non-infectious diseases are haemophilia, cancer, allergy and rheumatoid arthritis.

The diseases can be prevented by education people about the disease. Besides this personal and public health measures like proper disposal of waste, decontamination of drinking water, and control of vectors are required.
Our immune system plays the major role in preventing these diseases. Immunity can be inborn or acquired.
Inborn immunity is a non-specific type of defense present in body since birth.Acquired immunity is pathogen specific and activated only when the body encounters the pathogen.It is mediated by two lymphocytes: B cells and T cells.The B cells secrete five classes of antibodies: IgM, IgA, IgG, IgD and IgE. The T cells provide cell-mediated immunity. The acquired immunity is of two types: active immunity and passive immunity.

Auto immunity is the evolution of acquired immunity in higher vertebrates based on ability to differentiate foreign molecules and organisms from self molecules. Some examples of autoimmune diseases are multiple sclerosis, myasthenia gravis and rheumatoid arthritis.
The response of immune system to specific environmental substances (Allergen) is called allergy.
Vaccination and immunisation is the administration of antigenic material (the vaccine) into the body that produces immunity to a disease.
Immune system comprises of lymphoid organs, tissues, cells and soluble molecules like antibodies. Lymphoid organ comprises of primary lymphoid organs and secondary lymphoid organs.
Among other diseases, AIDS and cancer kill a large number of individuals worldwide.
AIDS stands for Acquired Immune Deficiency Syndrome. It is caused by Human Immuno deficiency Virus or HIV. It is detected by ELISA and Western Blot tests. There is no cure for AIDS.

Cancer is caused due the uncontrolled division of cells in a part of the body that usually results in malignant tumor. It can be detected by:Biopsy, X-rays, CT Scan, Magnetic Resonance Imaging. Cancer can be treated by surgery,radiotherapy,chemotherapy and immunotherapy

Millions of people, including young adolescents, around the world are addicted to narcotics and alcohol.

Addiction to drugs and alcohol occurs due to:Curiosity, peer pressure, family problems, academic stress and, desire to enhance physical endurance.

Addiction to drugs and alcohol can be prevented by counseling a child and encouraging him to discuss his problems with parents and friends.

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