Characterization of Viruses
A virus is a miniscule, acellular, infectious agent having one or several pieces of nucleic acid, either DNA or RNA, but never both.
Pasteur first defined them as a "living thing smaller than bacteria" and termed them virus- Latin for poison.
In 1884 the first vaccine for rabies was developed. Rabies is 100% fatal without this vaccine.
In 1898, viral studies intensified as foot/mouth disease was discovered and was found to be non-cellular.
In the 1950's the study of virology emerged as a science.
_B) Virus Terminology
- Non-living agent with either DNA or RNA but never both
- Nucleic acid is surrounded by a protein coat called a capsid
- The shape is determined by the capsid
- They are associated with all life forms- all organisms contain viruses
- Usual ranges in size is 1/100 to 1/1,000 of the size of a host cell
- Viruses have an extracellular state, called a viroin, consisting of a protein coat called the capsid.
- They lack a cytoplasmic membrane and have no cytosol.
- An envelope can be on selected virus types and is made of a lipid bilayer over the capsid
_C) Virus Types
- Naked-- lacks an envelope and is hardest to control
- Enveloped--easier to kill and normally infects humans
- There are two states of a virus. (1) Chemically inert being outside of the host, and (2) Viroin state- replicating within a host.
Helical shape, usually infectious of plants and animals (example from tobacco mosaic virus)
Viral envelope (example from herpesvirus family)