Virus is Latin word which means poison.
Discovery: -
Viruses were discovered by Iwanowsky in 1892 from infected leaves of tobacco.
Living or Non-living: -
They have characteristics of living and non-living things. When they enter in the body
of living organisms they reproduce like living things. But when they are outside of the
body they form crystals like non-living things.
Size & Shape: -
Their size is from 0.01m to 0.3m. They are rounded, rod shaped, polyhedral and
tadpoles in shape.
Structure: -
They are chemically alike and have two parts: -
i) An outer coat of protein. This coat determines the shape of virus. It
consists of two parts Head & Tail.
ii) An inner core of DNA or RNA. DNA is present in head region. Animal
viruses contain DNA and plant viruses have RNA.
Nutrition: -
They cannot prepare their own food. All viruses are parasites and obtain food from
host.
Reproduction: -
They reproduce when they enter in the body of host.
Diseases: -
i) In plants virus cause many diseases. For example ring spot in many
plants. Yellow in sugar beet and mosaic in tobacco, potato and tomato
etc.
ii) In animals virus cause mouth and food diseases. Cowpox in horses and
cows.
iii) In human virus cause cold, influenza, smallpox, polio, hepatitis, cancer
and AIDs etc.
Sources of Transmission: -
i) Through droplets due to coughing.
ii) Through droplets due to sneezing.
iii) Through physical contact.
iv) By air and contaminated water and food.
v) By re-use of already used syringes.
vi) By un-sterilized surgery equipments.