Are Viruses .. Alive ?

Our nasty little friends (more so foes) have only been discovered a little over a century ago, with the first ever virus discovered in 1892, the tobacco mosaic virus, by Russian biologist Dmitry Ivanovsky.

Ever since, our attitude towards them hasn't been that friendly. Well .. they started it.

And while we define viruses in terms of their ability for infection, filtration,... among other criteria, yet can we classify viruses as alive?

What defines being alive?

MRS GREN, is a "fictional" old teacher of biology (unless she teaches at your school), who also happens to be an ACRONYM that defines how to characterize living things - also sometimes referred to as MRS C GREN.

This basically stands for:
Movement, Respiration, Sensitivity, Control (Homeostasis)[in the MRS C GREN version], Growth, Reproduction, Excretion, and Nutrition.

Viruses fail some of the basic characteristics noted above. They are as alive in this definition as a rock would be.
One example to clarify this further is one given by Dr Amesh Adalja,

Take a cat, a plant and a rock, and leave them in a room for days. Come back, and the cat and the plant will have changed, but the rock will essentially be the same...
[Viruses] are inert unless they come into contact with a living cell

So basically, viruses can be considered as static organic particles, missing self-generated and/or self-sustaining actions.

Add to that, viruses actually require proper contact and a host to initiate their reproduction cycle, as they lack the proper machinery for reproduction themselves. This happens when Virions - Virus particles - infect host cells, and start using them to replicate.

Although one study in 2015, led by Genomic Biology professor Gustavo Caetano-Anollés, announced that viruses can be actually identified as alive via looking at folds - protein structures - encoded in virus genomes. Quoting him on the findings:

In fact, the remnants of ancient viral infiltrations are now permanent features of the genomes of most cellular organisms, including humans. This knack for moving genetic material around may be evidence of viruses' primary role as "spreaders of diversity"

and also

Viruses now merit a place in the tree of life. Obviously, there is much more to viruses than we once thought.

Yet, even with the above findings, with the current definition of alive, viruses might still not make it there, unless we agree to his advise:

They simply have an atypical mode of living that is slightly different from ours. They are not fully independent. Instead, they move in and out of our bodies, stealing the resources and producing their offspring. In short, we need to broaden how we define life and its associated activities

Whether you agree with the existing definition of alive, or prefer to adopt the wider notion and consider viruses alive..
Dead, alive, or zombie, stay alert!

Thank you for reading through!

@mcfarhat

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