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Human Diseases Pdf Download Notes For SSC CGL 2017,UPSC,NDA,CDS

What is a disease?

  • Any condition which interferes with the normal functioning of the body is called a disease.
  • In other words, disease may be defined as a disorder in the physical, physiological, psychological or social state of a person caused due to nutritional deficiency, physiological disorder, genetic disorder, pathogen or any other reason.

Types of Diseases

The diseases may be classified into two broad categories (Table 28.1).

Human Diseases Pdf Download Notes For SSC CGL 2017,UPSC,NDA,CDS

Human Diseases Pdf Download Notes For SSC CGL 2017,UPSC,NDA,CDS

A. Congenital disease : The disease which is present from birth (e.g. hole in the heart in infants). They are caused by some genetic abnormality or metabolic disorder or malfunctioning of an organ.

B. Acquired disease : The disease which may occur after birth during one’s lifetime.

Acquired diseases may generally be classified into :

(i) Infectious diseases : The diseases which can be transmitted from person to person e.g. measles.

(ii) Degenerative diseases : The diseases caused by the malfunction of some vital organs of the body e.g. heart failure.

(iii) Deficiency diseases : These are caused due to nutritional deficiency such as that of minerals or vitamins in the diet e.g. anaemia (Fe, Beri- beri (vitamin B). You have read about such diseases in an earlier lesson 27. (iv) Cancer : This is an abnormal, uncontrolled and unwanted growth of cells. e.g. breast cancer.

Acquired diseases are studied under two categories

 (i) Communicable diseases : The diseases which can be transmitted from an infected person to a healthy person.

(ii) Non-communicable diseases : These diseases do not spread from an affected person to a healthy person

Modes of Spread of Communicable Diseases Communicable diseases spread from the infected person to a healthy person in the following ways.

Direct transmission The pathogens of diseases infect a healthy person directly without an intermediate agent. It can take place by various means such as,

  1. Direct contact between the infected person and the healthy person : Diseases like small pox, chicken pox, syphilis, gonorrhoea spread through direct contact.
  2. Droplet infection : The infected person throws out tiny droplets of mucus by coughing, sneezing or spitting. These droplets may contain the pathogen. By inhaling the air containing the droplets, a healthy person may get the infection. Diseases like common cold, pneumonia, influenza, measles, tuberculosis and whooping cough spread through droplet infection.
  3. Contact with soil contaminated with disease-causing viruses, bacteria etc.
  4. Animal bite : Viruses of rabies are introduced through the wound caused by the bite of rabid animals, especially dogs. The virus is present in the saliva of the rabid animals.

Indirect transmission

The pathogens of certain diseases reach the human body through some intermediate agents. It can take place by various means, which are as follows :

  1. By vectors such as houseflies, mosquitoes, and cockroaches. Examples: Houseflies carry the causative organisms of cholera on their legs and mouth parts from the faeces and sputum of infected persons to food and drinks and contaminate them. When this contaminated food is taken by a healthy person, he gets the infection. Similarly, mosquitoes carry virus of dengue and malarial parasite which causes malaria.
  2. Air-borne : The pathogens may reach humans with air and dust. The epidemic typhus spreads by inhalation of dried faeces of infected fly.
  3. Object borne (Fonite borne) : Many diseases are transmitted through the use of contaminated articles, such as clothes, utensils, toys, door handles, taps, syringes and surgical instruments, etc.
  4. Water borne : If potable water (drinking water) is contaminated with pathogens of diseases such as cholera, diarhhoea, hepatitis or jaundice, it reaches a healthy person upon consuming such water.


  • Pathogen : A living organism which causes a disease.
  • Parasite : An organism which gets food and shelter from host.
  • Host : The living body on or inside which the disease-producing organism takes shelter.
  • Infestation : A large number of parasitic organisms present on the surface of body of the host or on the clothings.
  • Vector : It is an organism which harbours a pathogen and may pass it on to another person to cause a disease (Mosquitoes harbour malarial parasite and transmits it to humans).
  • Carrier : It is an organism which itself does not harbour the pathogen but physically transmits it to another person (Housefly is the carrier of cholera germs).
  • Reservoir : An organism which harbours pathogen in large numbers and does not suffer itself.
  • Epidemic : Spreading of a disease among a large number of people in the same place for some time e.g. plague.
  • Endemic : A disease which is regularly found among a particular group of people e.g. goitre.
  • Pandemic : A disease which is found all over the world e.g. AIDS.
  • Interferon : Type of proteins produced by infected cells of the body when attacked by a virus, which act to prevent the further development of the virus.
  • Inoculation : Introduction of antigenic material inside the body to prevent suffering from a disease.
  • Vaccination : Injection of a weak strain of a specific bacterium (Vaccine) in order to secure immunity against the corresponding disease. It is also called immunisation.
  • Incubation period : The period between entry of pathogen inside a healthy body and appearance of the symptoms of the disease. Symptoms : Specific expressions which appear on the diseased and help in the identification of the disease


The diseases which spread from one person to another through contaminated food, water or contact or through insecticides, animals etc. are called the communicable diseases. These are caused by different causative agents (pathogens).

Diseases caused by viruses

  • Chicken pox Pathogen : Chicken pox virus (varicella)
  • Mode of transmission : By contact or through scabs
  • Incubation period : 12-20 days


  • Fever, headache and loss of appetite
  • Dark red-coloured rash on the back and chest which spreads on the whole body. Later, rashes change into vessicles.
  • After few days these vessicles start drying up and scabs (crusts) are formed.
  • These scabs start falling (infective stage)

Prevention and cure

There is no vaccine against chicken pox as yet. But precautions must be taken as follows:

  1. The patient should be kept in isolation.
  2. Clothings, utencils, etc. used by the patient should be sterilised.
  3. Fallen scabs should be collected and burnt. One attack of chicken pox gives life long immunity to the person recovered from this disease


  • Pathogen : Virus (Rubeola)
  • Mode of transmission : By air
  • Incubation period : 3-5 days


  • Common cold
  • Appearance of small white patches in mouth and throat.
  • Appearance of rashes on the body.

Prevention and cure

  • The patient should be kept in isolation.
  • Cleanliness should be maintained.
  • Antibiotics check only the secondary infections which can easily occur


  • Pathogen : Polio Virus
  • Mode of transmissions : Virus enters inside the body through food or water.
  • Incubation period : 7-14 days


  • The virus multi pliesin intestinal cells and then reaches the brain through blood.
  • It damages brain and nerves and causes infantile paralysis.
  • Stiffness of neck, fever, loss of head support.

Prevention and Cure

  • Polio vaccine drop (oral polio vaccine, OPV) are given to children at certain
  • Pulse polio programme is organised in our country to give polio vaccine to

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Human Diseases Pdf Download Notes For SSC CGL 2017,UPSC,NDA,CDS