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Virus | what is virus | classification of viruses | The Baltimore

Updated: Aug 9





Today, the human beings all over the world are living under the threat and non-pharmaceuticals practices protocols of life due to COVID-19. But to before to discuss on covid19 it’s better to know what is virus? From where it’s coming and from where it is vanishing.

Viruses are the smallest of all the microbes having the size 20–400 nm with a diameter about 80 nm. Viruses are microscopic parasites. Until 1930s most of the scientists were of the opinion that viruses are small bacteria but after the invention of electron microscope by the physicist Ernst Ruska in 1931, every opinion about the virus was changed. In electron microscope, a beam of accelerated electrons is used and it has very high magnifying power and resolving power. With this device, virus was found to be a distinct entity containing genetic material in the form of DNA or RNA. Viruses are so small that billions of viruses can fit on the head of a pin.

Viruses are simply packets of nucleic acid either DNA or RNA surrounded by a protein shell and sometimes fatty materials called lipids. A virus can only replicate inside the cell of a host organism that may be an animal, plant as well as a bacteria. Viruses have no ability to metabolize on their own that is one of the main reason that so many researcher claimed that virus is a nonliving. Virus require a host organism for the manufacture of chemicals which are essential for their replication as they lack the capacity to thrive and reproduce outside of a host body. Their life form is totally different from that of a cellular organism.

As the virus enters a host cell, it activates itself and hijacks the metabolic machinery of the cell in order to replicate itself. The reproduction rate is so high and fast that very soon the viruses burst out of the infected cell and subsequently invade other healthy cells. So the viruses kill the cells of the host organism or disrupt their function. In multi-cellular organism, if the cells in a large number die, the whole organism may suffer gross metabolic disruption or even cause mortality. Virus is such a common name today that even if we get normal fever or flu, the doctor says that it’s a viral fever. But there is a much dangerous viruses in the world today like coronavirus which has been creating a fear among the people.

Do you know?

Many people at the idea of calling viruses “a living thing” because they are so simple, composed of nucleic acid (DNA or RNA) and an outer structure that “holds” the contents together. A protein coat known as a capsid.

As far as I am concerned even though they may be obligate parasites (as are some bacteria), their basic structure and ability to replicate is why I refer to them as living but I shall write an articles very soon on viruses are living or nonliving.


In response to the viral infection, the immune system of the host organism springs in to action. White blood cells (WBC), antibodies and other mechanism start working to get rid the body of host organism of the viruses. Sometimes the body of the infected person responds with fever because increase in body-temperature inactivates some viruses. Virally infected cells produce and release small proteins called interferons which prevent replication of viruses. These proteins also act as signaling molecules to warn nearby cells of a viral presence. Unfortunately in some human beings, viral infection outpaces the immune system. Such cases not only cause danger to the lives of the infected persons but also contribute to uninterrupted reproduction of viruses.

Corona virus COVID-19 appears to be a positive-stranded RNA virus with a crown like appearance when observed under electron microscope. Initially, it was transferred to humans from animals (I am performing a private research from which animal it came from) but now it has the ability of human to human transmission also. The most common symptoms of Covid-19 are fever, tiredness and dry cough. Some patients may have running nose, sore throat, nasal congestion, aches, pain or diarrhea. I must recommend to check your local guidelines as now I am listening the news that covid-19 is changing its shapes also symptoms .

And because coronaviruses can survive in living cells only, hence they cannot be cultured (and it is very difficult) in artificial media for the development of vaccine. Till present date, no vaccine has been developed for coronavirus infection.

Human activity is a vital reason for “emerging viral infection and diseases” because of a process called “spillover”. This refers to a disease caused by a pathogen which lives within a host animal without causing a disease in that host, but when infecting another animal (like humans) may cause severe disease. That is the story of how AIDS became a worldwide disease.

Classification of viruses Viruses are not classified taxonomically that living organisms are. https://en.wikipedia.org/wiki/Virus_classification

The Baltimore Classification of viruses is based on the method of viral mRNA Production. Viruses must generate mRNAs from their genomes to produce proteins and replicate themselves, but different mechanisms are used to achieve this in each virus family. Viral genomes may be single-stranded (ss) or double-stranded (ds), RNA or DNA, and may or may not use reverse transcriptase (RT). In addition, ssRNA viruses may be either sense

(+) or antisense (−). This classification places viruses into seven groups:

I: dsDNA viruses (e.g. Adenoviruses, Herpesviruses, Poxviruses)

II: ssDNA viruses (+ strand or "sense") DNA (e.g. Parvoviruses)

III: dsRNA viruses (e.g. Reoviruses)

IV: (+)ssRNA viruses (+ strand or sense) RNA (e.g. Picornaviruses, Togaviruses)

V: (−)ssRNA viruses (− strand or antisense) RNA (e.g. Orthomyxoviruses, Rhabdoviruses)

VI: ssRNA-RT viruses (+ strand or sense) RNA with DNA intermediate in life-cycle (e.g. Retroviruses)

VII: dsDNA-RT viruses DNA with RNA intermediate in life-cycle (e.g. Hepadnaviruses)

The complete set of viruses in an organism or habitat is called the virome; for example, all human viruses constitute the human virome

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