1. VIRUS

2. Discovery : He contributed in the discovery of first virus from Tobacco mosaic virus. Ivanovsky reported in 1892 that extracts from infected leaves were still infectious after filtration through a Chamberland filter-candle.

3. DEFINITION: Virus, an infectious agent of small size and simple composition that can multiply only in living cells of animals, plants, or bacteria. The name is from a Latin word meaning “slimy liquid” or “poison.”

4. VIRUSES OCCUPY A SPECIAL TAXONOMIC POSITION

5. TYPES OF VIRUSES: Link

6. STRUCTURE:

7. Shapes (Virus):Virus

8. CHARACTERISTICS OF VIRUSES: They are enclosed in a protective envelope. They have spikes, which helps them to attach to the host cell. They are non cellular. They do not respire, do not metabolize and do not grow but they do reproduce. They contain a protein coat called the capsid. They have a nucleic acid core containing DNA or RNA. Ribosomes and enzymes are absent, which are needed for metabolism. They are considered both as living and non living things, as viruses are inactive when they are present outside of host cells and are active in side of host cells. As they make use of raw materials and enzymes of the host cell to reproduce and causes several infections.

9. CLASSIFICATION :

10. Lytic Cycle: 1.Attachment: Virus attaches to the host cell. 2.Entry: Genetic material is injected into the host cell. 3.Replication: Virus takes over the cells metabolism causing the creation of new proteins and nucleic acids by the host cell's organelles. 4.Assembly: Proteins and nucleic acids are assembled into viruses. 5.Release: Virus enzyme cause the cell to burst and viruses are released from the host cell. These new viruses can infect other cells.

13. Lysogenic Cycle:

15. VIRAL DISEASES: Viral diseases are extremely widespread infections caused by viruses, a type of microorganism. There are many types of viruses that cause a wide variety of viral diseases. The most common type of viral disease is the common cold, which is caused by a viral infection of the upper respiratory tract (nose and throat). Other common viral diseases include: Chickenpox Flu (influenza) Herpes Human immunodeficiency virus (HIV/AIDS) Mumps, measles and rubella Shingles Viral gastroenteritis (stomach flu) Viral hepatitis Viral pneumonia

16. ADVATANGES: They are use full in delivering genes to target cells and play a vital role in and gene therapy researches DISADVANTAGES: There are many pathogenic viruses, which causes harm for human beings, plants and animals. In human beings the diseases caused by viruses are: HIV, influenza, herpes, hepatitis small pox, cowpox, etc. The diseases caused by viruses in plants are tobacco mosaic viruses, etc. The diseases caused by bacteria in animals are bovine tuberculosis and etc.

17. PREVENTION AND CONTROL OF VIRAL DISEASES: Vaccination Quarantine Hygiene and Sanitation Vector Control Life Style Changes