The Virus world and Us


Have you ever imagined of one of the most successful survivors of evolution? One of the most interesting species that has co-evolved with humans since several thousands of years.

An electron microscope image of Smallpox virus (Source: http://www.who.int/about/bugs_drugs_smoke_chapter_1_smallpox.pdf)

A virus is basically an acellular system which contains either DNA or RNA surrounded by a coat of proteins. They are obligate (restricted to a particular mode of life); intracellular (within the cell); parasite (an organism that lives on another organism and benefits by deriving nutrients at other’s expense). They live a kind of borrowed life by utilizing the machinery of any living cell. It is the nasty part of the environment that kills the susceptible host. Such a versatile species is known to infect a range of hosts – Bacteria, Algae, Archae, Invertebrates, Plants and Animals.

Viruses are lifeless entities that encompass the molecular machinery for life. These molecular machines are inanimate, but once it has interacted with a living cell; it is considered alive. So, most scientists consider virus an as organism both dead and alive. They have a genetic potential to reproduce and they do so by being metabolically active, i.e. by infecting a cell. The virus itself is non-infectious; however, once the genetic material is injected and delivered to the living cells, it releases as many as 100000 copies of the infectious form ‘virion.’

Relative sizes of Biological entities (Source: Acheson NH. Fundamentals of molecular virology)

The typical size of the virus ranges from approximately 20-350nm in diameter. For example, the HIV (Human Immunodeficiency Virus) is 100nm in diameter which is 1000 times smaller than that of a normal cell. It is about 10000 times smaller than that of Paramecium which is visible to the naked eye. So imagine how tiny a virus could be!

There are about 10-50 million bacteriophages ( the virus that infects bacteria) on average per ml of seawater and even many more in many soils. This is about 10-fold greater than the estimated number of bacteria. The surprising fact is that if these 1031 phages are lined together end to end; it could stretch some 200 million light years into space; that is far into the universe beyond many of our known neighboring galaxies. About 95-98% of the total organisms of the marine are microbial and remaining 2% includes the other forms of life. It is estimated that 20% of the microbes of the earth’s ocean are destroyed each day by virus infection. The amount of virus present in the ocean and the extent of interaction between the virus and the host is immense.  About 1031 viruses of the Earth’s ocean are killed every day by UV radiation and the same number builds back due to its massive replication rate. Such an ancient giant pool of viruses that have co-existed till present; how they affect our very existence is the big picture.

Human epidemics have occurred due to highly contagious acute viruses such as Smallpox virus, Influenza virus, Coronavirus, etc. However, persistent viruses such as HSV (Herpes Simplex Virus), VZV (Varicella Zoster Virus), Papillomavirus etc have caused major damage to humankind.

Rash as seen in smallpox virus infection
Influenza virus causing respiratory illness
Orofacial Herpes Simplex Virus Infection    
Genital warts in Human Papilloma Virus infection

Image Source: Mandell, Douglas, and Bennett’s Principles and Practice of Infectious Diseases (Eighth Edition)

This is a never-ending story to our lives being touched by viral influences and most of them showing its lasting evidence of viral footprints

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