Infectious Disease

A disease is an abnormal condition of an organism’s body or its part due to some infection or environmental conditions.

The disease causing organisms are called pathogens.

The communicable diseases are transmitted directly through an infected individual or indirectly through a vector.

An insect or any living carrier that transmits an infection without getting infected themselves is called a vector.

The transmission of a pathogenic disease can be direct or indirect.

The direct transmission of a disease occurs from an infected person to a healthy person directly.Examples of such diseases include measles, chicken pox and fungal infections.

The indirect transmission of a disease occurs by touching and sharing of items used by an infected person, consumption of contaminated food and drink, vectors and air for example, tuberculosis etc.

Pathogens can be bacteria, virus, protozoans, fungi, worms, mites etc.

Some diseases caused by viruses are common cold, influenza, mumps, smallpox, poliomyelitis, measles, rabies, jaundice and AIDS.

Some diseases caused by bacteria are tuberculosis, diphtheria, tetanus, whooping cough, pneumonia, cholera, syphilis and typhoid.

Some diseases caused by moulds and fungi are ringworm and athlete’s foot.

Some diseases caused by protozoa are malaria amoebiasis and sleeping sickness.

Some diseases caused by worms are elephantiasis, ascariasis, taeniasis and enterobiasis.

Scabies is a disease, caused by mites.

Some diseases caused by rickettsiae are tick fever and typhus fever.


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  • Q1

    Name a bacterial disease that spreads by ingesting contaminated food and water. Enlist any two symptoms of this disease.


    The bacterial disease that spreads by ingesting the contaminated food and water is cholera.

    Symptoms of cholera are:

    • Vomiting
    • Whitish and watery stool (rice water-like appearance), which results into excessive dehydration and loss of minerals

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  • Q2

    What are the measures to prevent cholera.


    The following measures can be used to prevent cholera:

    • Boil the drinking water and properly heat the food.
    • Proper disposal of waste and maintenance of hygienic conditions.
    • Cover the eatables so that they don’t get contaminated by flies.
    • Get immunised against cholera with the help of cholera vaccines.

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  • Q3

    Write the full forms of the following abbreviations:

    a. BCG Vaccine

    b. DOTS


    The full forms of the abbreviations are:

    a. BCG Vaccine: Bacillus-Calmette-Guerin vaccine

    b. DOTS : Directly Observed Treatment, Short course

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  • Q4

    Name the causative agent of cholera.


    Cholera is caused by bacterium Vibrio cholerae.

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  • Q5

    Give examples of two common bacterial diseases.


    Two common bacterial diseases are:

    a. Cholera

    b. Tuberculosis

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