Viruses
About a century ago at the time of Louis Pasteur (1822-1895) and Robert Koch (1843-1910), the word "virus" was generally referred to as a poison associated with disease and death.
Present notation
Now viruses are recognized as particles of nucleic acid often with a protein coat.
Properties
They replicate in living cells and cause many diseases such as influenza, hepatitis, small pox and AIDS.
Bacteriophages
bacterial viruses, also known as bacteriophages.
Virology
The branch which deals with the study of viruses is known as virology.
Word meaning
The word virus is derived from Latin word venome meaning poisonous fluid.
1st vaccination
In 1796, Edward Jenner first vaccinated an, 8 years old boy with material removed from cowpox lesion on the hand of milkmaid. After six weeks the boy was inoculated with pus from a small pox victim, but he did not develop the discase. Later, Jenner used material for vaccination from cowpox lesions and successfully vaccinated 23 persons.
Origin of word vaccine
the material he used was obtained from cow (latin vacca), latter the term vaccination was used by Louis Pasteur for inoculation against disease.
Charles Chamberland, found that bacteria
can not pass through porcelain filters.
while agent responsible for rabies
can pass through these filters.
tobacco mosaic disease
In 1892, Ivanowski discovered that the agent which caused tobacco mosaic disease was filterable.
Bacteriophages discovery
Bacteriophages, viruses that infect bacteria, were discovered independently by Twort in 1915 and D'Herelle in 1917.
Discovery of lysis phenomenon
Twort observed that bacterial colonies sometimes undergo Lysis (dissolved and disappeared) and that this lysis can be transferred from one colony to other.
Bacteriophage meaning
word bacteriophages meaning "bacteria eater".
Purification 
The filterable agents were first purified in 1935, when Stanley was successful in crystallizing the tobacco mosaic virus. Chemical analysis of these particles showed that they contained only nucleic acid and protein. This suggested that, unlike other forms, viruses are of simple chemical composition.
Classification of viruses
- Virus morphology
- nucleic acid
- genetic material may be DNA or RNA naked. enveloped or complex.
Small pox
DNA enveloped virus)
Herpes simplex:
(DNA virus)
In this vascular lesions in the epithelial layers of ectodermal tissues are formed. Most commonly this disease occurs in the mouth, on the lips, and at other skin sites.
Influenza:
enveloped RNA viruses.
Influenza virus exists in three forms called A, B, C. Influenza viruses are the only members of orthomyxovirus family.
The envelope is covered with hemaglutinin and a neuraminidase, both are the type specific antigens.
Influenza virus is composed of a segmented single-stranded RNA genome,
Mumps and Measles:
belong to group paramyxoviruses.
They are large enveloped, RNA viruses.
Polio:
Poliomyelitis, caused by polio virus,polioviruses are the smaller known viruses and contain RNA in spherical capsid.
Retroviruses
The most familiar of viruses is the human immunodeficiency virus (HIV) which causes acquired immune deficiency syndrome (AIDS).
The single stranded RNA tumor viruses, which also include retroviruses (oncoviruses), are spherical in form about 100nm in diameter and enveloped by host plasma membrane.
special enzyme
The retroviruses have a special enzyme called reverse transcriptase, which can convert a single-stranded RNA genome into double stranded viral DNA.
Not only this DNA can infect host cells, but it also can be incorporated into host genome as a provirus that can be passed on to progeny cells. In this way some of retroviruses can convert normal celis into cancer cells.
RNA tumor viruses have been known for many years.
| DNA VIRUSES | |
|---|---|
| Double Stranded DNA | |
| Pox | Poxvirus |
| Herpes | Herpesvirus |
| Hepatitis B | Hepadnavirus |
| single Stranded DNA | |
| Bacteriophage | Parvovirus |
| Single Stranded RNA | |
| HIV | Retrovirus |
| Rubella | |
| Hepatitis A | |
| Hepatitis C | |
| Double Stranded RNA | |
| Retrovirus | Diarrhea |
| DNA VIRUSES | |
|---|---|