Viruses: Dead Devious Microscopic Capsules

This article is Part Two of the mini-series on Viruses. This post is written in response to the popular demand, and questions raised in Part 1 of the series. This post looks to introduce to you what viruses are, how they were discovered, the basic structure of a virus and how a virus can affect our cells. In addition to this, I have also added some brief information on how long a virus can survive.

Part 1 gave a brief background on the novel coronavirus outbreak and provided basic prevention measures against the virus. Since there is no cure or treatment for the recent outbreak, it is highly recommended that you take precautionary measure as far as is reasonably practicable. A link to Part 1 can be found here.

Do viruses have life?!?

Further to the Coronavirus outbreak that erupted in the city of Wuhan, China, and has now unwelcomingly spread around the world – a number of you have had questions on viruses. A simple Google search very quickly reveals what may seem like the ‘worst’ – VIRUSES ARE (arguably) NOT ALIVE!

I know this sounds very science-fiction and unreal, but it’s true. Viruses are, by definition, not living organisms. Although ‘life’ is a very slippery term to define, scientists have provided 7 characteristics to determine whether something is a living or not. These criteria are as follows [1]:

1. Nutrition (“Eating”)
2. Respiration (“Breathing”)
3. Movement
4. Excretion (“Pooping”)
5. Growth
6. Reproduction
7. Sensitivity (Response to stimulus)

As viruses do not perform all of the above functions, they are technically not considered to be living. Viruses do not eat, or respire, or move of their own accord, or excrete. They are also incapable of growth.

Viruses however, use the resources of its host to make copies of itself – without the machinery of the host, viruses are unable to replicate/reproduce. They are therefore thought to be parasitic.

When DNA was discovered, it was thought to be the characteristic of the living [2]. Anything that had DNA, just had to be living. Think about it, it is not so far off from actual truth – a plant is living, because it has DNA. Same goes for a pet dog, humans and bacteria – all considered living because of the presence of genetic material.

As you have probably started to notice, viruses are arguably an intermediary between life and death. They have often been considered as by-products of cellular life, having potentially originated as escaped genes from cells [2]. The way I look at it, viruses are like a seed with the potential of parasitic life – they are able to bud under the right conditions. If the conditions are not ‘right’, they remain dormant/asleep.

It seems that the question of whether viruses are alive is therefore more a philosophical one than a scientific one, and the answer depends on your beliefs. Since they are able to command the host, to perform some of it’s prime functions of life – would you say they make the best of their situation, and are actually alive as “managerial systems”?

Viral Discovery

Before viruses were discovered, bacteria (and to some extent, fungi) were believed to be the only causal factor for infections. This was soon about to change.

In 1882, Dmitry Ivanovsky (a founder of virology) was commissioned in 1887 and 1890 by the Russian Department of Agriculture, to investigate the cause of the disease which had struck Russian tobacco plantations in Bessarabia and the Crimea region, accordingly [3].

Since it was known at the time that bacteria are a disease-causing entity, studies were focused to find the bacteria that affected the tobacco plantations. The experimental procedure was fairly simple. Since it was plants that were being studied, the leaves and sap of the diseased plants would be crushed and juiced. The juices would then be passed through a special micro-filter, that would filter out any leaf/stems but also more importantly filter out microscopic bacteria. Once filtered, the sap passing out of the filter would be used to inoculate healthy plants.

In these experiments, it was hypothesised that the causal bacteria would be filtered out and therefore the plants would not be affected. The strain of bacteria would then be available to further study disease progression and its mechanism. However, it never got to this. What Ivanovsky found instead, was surprising. He discovered that the filtered juice he obtained from the diseased plants infected nine of ten healthy plants he inoculated. No bacterial culture could be identified from it.

Following this research, he wrote the paper “Concerning the mosaic disease of the tobacco plant”, and found that the sap of leaves infected with tobacco mosaic disease retained its infectious properties even after filtration” [3, 4]. At this point in time, it was concluded that the bacteria was particularly difficult to study as it could not be isolated and cultivated in the laboratory.

Ivanovsky carried out further research on the subject from his time in Crimea and concluded, as in his paper of 1892 that the disease in these plants was caused by a “filterable infectious agent.” His filtration experiments were the first step in the discovery of viruses [3].

Further to Ivanovsky’s research, Martinus Beijerinck found in 1898 that the tobacco mosaic disease was caused by agents that would multiply within living plants. He found no sign of replication of these agents outside the plant where the plants were growing [3].

Structure of a virus

There are different types of viruses, and they do not all look alike. Simply speaking, a virus can look a lot like the medical capsules you take when you’re ill, except they are much much smaller.

Image highlighting the structure of a virus. More specifically, the image is of the SARS-CoV-2 virus which causes COVID-19.

An inert viral capsule has some genetic information, a few proteins and some sugars stored inside of it. The surface of the capsules look like spikes.

So if viruses are arguably dead, how do they cause disease?

The “spikes” on the viral capsule are proteins that allow the virus to communicate with and bind to the host cell, thereby providing a route by which to affect/commandeer them.

Once they bind to the host, the virus will insert its genetic material into the healthy living cell. This is the point of time at which where the virus begins to affect the host cell. Through the proteins and sugars that they carry, viruses invade healthy living cells and take command of them.

A virus will direct the host cell to manufacture bulk quantities of the virus, via a pre-written step by step process. It then commandeers the host cell make different parts of the virus’ body. These are then assembled together to produce new (“baby”) viruses.

The over-production of viruses can kill, damage or change the genetic material of the host cell. The effects that viruses can have on a host organism are largely variable – some of them can cause cancers, others just a wart, or some can cause the flu. Some viruses can also modify the host-cell processes to maximize viral replication [5].

Can viruses die?

Again, the answer here depends on your belief – how can something that never lived, die? Keeping philosophy aside, most viruses generally cannot survive outside of a host cell for more than 24 hours. Although there are exceptions, and some viruses can last outside of the body for slightly longer. They can certainly not perpetually survive without a host.

For this reason, it is recommended that in cases of viral outbreaks like COVID-19 that one takes precautionary measures as far as is reasonably practicable. Among other precautionary measures, ensure that you practice basic respiratory hygiene, wash your hands often, and avoid touching your eyes, nose and mouth. Further advice on precautions is provided in Part 1 of this mini-series.

For Part One of this mini-series, please click here.

References:

1. https://assets.cambridge.org/97805216/80547/excerpt/9780521680547_excerpt.pdf
2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2837877/
3. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC241285/
4. https://www.ncbi.nlm.nih.gov/pubmed/11570281
5. https://www.ncbi.nlm.nih.gov/books/NBK21523/