Virus introduction,definition, classification , structure mode of transmission

Virus introduction,definition, classification , structure mode of transmission

August 03, 2022
DEFINITION 
A virus is an infectious microbe having  a segment of nucleic acid (either DNA or RNA) surrounded by a protein coat. A virus cannot replicate alone; instead, it must infect cells and use components of the host cell to make copies of itself.

Viruses are first recognised in 1892 by the Russian scientist Dmitry I. Ivanovsky and in 1898 by the Dutch scientist .Martinus W.Beijerinck first surmised that the virus under study was a new kind of  infectious agent, which he designated contagium vivum fluidum, meaning that it was a live, reproducing organism that differed from other organisms.
SIZE
A virus is the smallest type of parasite to exist and is typically within the size range of 0.02 to 0.3 micrometers (μm) in size; however, some viruses can be as large as 1 μm.
Classification 
A virus is often classified according to its physicochemical properties, genome structure, size, morphology, and molecular processes. 
In terms of their genetic material, viruses are classified according to whether they are RNA or DNA viruses and the strandedness of their genetic material, which can include double-stranded (ds), single-stranded (ss), or partially ds. Furthermore, ss viruses will also be classified as to whether they are positive ss, negative ss, or negative with ambisense viruses.
To date, five dsDNA human virus families have been identified, of which include adenoviridae, herpesviridae, papillomaviridae, parvoviridae, and poxivirdae.

Examples of ds DNA viruses-
  1. Simian virus 40(SV40).
  2. Bacteriophages. 
  3. Herpes simplex.

                    Bacteriophages
Picobirnaviridae, picornaviridae, and reoviridae are the three human dsRNA viruses that have been identified.
dsRNA virus-
  1. Orthoreovirus.
  2. Cypovirus.
  3. Rotavirus.
  4. Bluetongue virus.

According to capsid morphology 

Viruses may be of various shapes i.e.
icosahedral, helical, or complex shapes 



STRUCTURE 
Viruses are very simple in structure they have following properties.
  • Virus have genetic material either DNA or RNA.
  • Enclosed by a protective protein coat called as capsid.
  • Capsids are made up of proteins subunits called capsomeres.
  • And these capsomeres composed of smaller protein subunits called protomers.
  • The proteins are encoded by nucleic acids which are enclosed by capsid itself.
  • Tne nucleic acids present in viruses is either DNA or RNA.
  • In some viruses the viral capsid is also surrounded by a lipid bilayer which is derived from host cell and called coat.
  • This coat increases the infectivity of the virus.
The entire virus particle present outside the host cell is called virion.



Viruses do not have the mechanisms needed to survive independently and needs plant, animal, or bacterial host cells where they can use those cell's machinery to replicate. Therefore, viruses uses different transmission routes to infect host cells, of which include direct contact, indirect, common vehicle, and airborne transmission.

Mechanism of infection 

The outer surface of the virus is very important  for its ability to recognize and attach to host cells. Surface of the virus have certain proteins that recognises and bind to cellular receptors to facilitate its attachment of virus  to the host cell.

Once the virus attaches to the host cell, it is engulfed through the cellular membrane by our defence cells and subsequently enters the cell’s cytoplasm. Inside the cell, the virus loses its viral coat i.e. (protein coat) into smaller cellular vesicles, and  releases its genetic material into the cytoplasm for its replication.

The genetic material of virus will attached with the host cells genetic material and direct them according to virus and replicates its genetic material and makes many copies of their genetic material and new virus particles these new virus particles now infect new host cell.

Mode of transmission 

Viruses are transmitted through defferent routes they may be transmitted through direct contact, indirect, using defferent vehicle, and air born transmission. 

Direct  contact transmission 

Direct contact transmission requires physical contact between infected person to non infected person it may transmitted by 
  • Kissing 
  • Sexual intercourse 
  • Biting(in case of animal host)
Examples 
  • HIV-1 (human immunodeficiency virus type 1)
  • HTLV-1( human T lymphotropic virus type 1)
  • HBV( hepatitis B virus)
  • Human papilloma virus.

Indirect transmission 

In this method viruses are transmitted through contaminated materials or objects as medical equipments. 

Air born transmission 

This is respiratory route of transmission of virus through droplets and respiratory secretion by sneezing coughing or even talking on hands and other objects.
Examples 
  • Influenza virus 
  • Rhinovirus
  • Parainfluenza virus 
  • Corona virus 

Common vehicle transmission 

In this method viruses are transmitted through contaminated food,water,medication& intravenous fluids feco-oral route.
Examples 
  • HAV(hepatitis A virus)- transmitted through feco-oral route.
  • Rotavirus through feco-oral route .


About

This is dummy text. It is not meant to be read. Accordingly, it is difficult to figure out when to end it. But then, this is dummy text. It is not meant to be read. Period.

Next
« Prev Post
Previous
Next Post »
Subscribe to: Post Comments (Atom)