Virology, a primer

By Dr F.S.L. IP

The words “virus” and “virome” are topical and it seems to me that the following could help towards better understanding.

It is taught that there are about 200 different strains of viruses causing the common cold; one third to one half of them are classified as rhinoviruses (rhino in Greek = nose, cf rhinoceros: kero = hard), about one-fifth as coronaviruses (corona in Latin = crown, from the fancied appearance when photographed) and among the rest figure adenoviruses (aden in Greek = gland) and influenza, so called because in medieval times such outbreaks were believed to be due to the nefarious influence of the stars and planets. (Likewise, malaria was attributed to bad air near stagnant water, marshes, etc.)

There are many viruses which cause fever, rashes, jaundice, haemorrhage, brain inflammation, etc., and specific diseases such as chickenpox, dengue, measles, etc.

Other viruses are associated with cancer, e.g. papillomaviruses. Bacteriophages make up another group, first discovered by F.W. Twort and so named in 1920 because he found them “eating” (phage in, in Greek = to eat) certain bacteria; these cause among others some attacks of acute gastro-enteritis e.g. E.coli phage type 011 or 0126, etc.

Louis Pasteur, a chemist and not medically trained, discovered that certain diseases are due to small cells such as bacteria and yeasts when he was called upon to study silk-worm disease, death of sheep from anthrax and spoilage of wine-making; all these diseases were threatening the silk industry, agriculture, farming, etc.

When tobacco plants were found to be stunted and their leaves spoiled, the disease was called Tobacco Mosaic Disease (TMD). A Dutch botanist, M.W. Beijerinck, in 1898 found that it was due to something that could pass through filters capable of keeping back bacteria and could transmit the disease to other tobacco plants and he called it a “filterable virus” (virus from Latin = poison)

N.M. Stanley in 1935 crystallised the TMD virus and found that when the crystals were dissolved in water they could transmit the disease. Such a fascinating substance which is both living, non-living and can be revived shocked biologists. J.F. Enders found that bacteria, but not viruses could be grown in test-tubes or in Petri dishes with the appropriate nutrients. However, he could get viruses to grow in chicken embryos which are living and developing organisms. This discovery is used for preparing influenza virus nowadays.

Later in 1949 he could get viruses to grow on parts of embryos, e.g. mumps in 1948 and polio in 1949.

In the 1940s viruses were found to be nucleo-proteins with a nucleic acid core and a shell made of protein. When nucleic acid was introduced alone into a living cell it could lead to more nucleic acid to be produced but also the appropriate protein shell. That shell has for its ability to provoke antibody formation against it, the immune response.

In 1955, working with bacteriophages (often simply called “phages”) H. Fraenkel-Conrat managed to separate the nucleic acid from the protein and put them back together. Thus he found that the nucleic acid, and not the protein, was responsible for virus activity. The protein helps in getting the nucleic acid into a cell.

Further study of the nucleic acid led to the discovery of the structure of the DNA, the well-known double helix.

Viruses can only survive, grow and multiply in a living cell, be it of animal or bacterial origin, or yeast; in other words, viruses are parasites. When the host call dies the virus particles parasitise fresh host cells. The host-cells themselves need the right conditions to grow and multiply. These include nutrient and water availability, oxygen (sometimes not e.g. tetanus spores), acidity or otherwise, protection from U-V rays, the right temperature, etc.

It is to be noted that so far Covid-19 seems to be spreading in the winter of the Northern Hemisphere.

To reach an epidemic level, the number of virus particles released with the death of the host-cells must exceed a critical level, on the closeness of potential patients to one another, whether fomites (inanimate bearers of infective particles) escape being disinfected, the number and mobility of animals harbouring or carrying the host-cells, and the level of immunity or defensive ability of the “target” population.

There is a kind of microorganism called Vibrio harveyi which illuminate certain beaches only when they have assembled in sufficient numbers, a form of intelligence or phenomenon called “quorum sensing” by biologists.

One may well ask whether it is possible that the host cells of viruses also decide when they (the viruses) have reached sufficient numbers so as to be expelled?

* * *

About global warming and conflicts, armed or not

On reading about global warming and climate change, it seems to me that an important factor has been overlooked, namely the armament industry.

To start with, how much energy, mostly from fossil fuel, is involved in mining the mineral ores, extracting the metals and shaping them into guns, cannons, bombs, rockets, etc., making vehicles such as lorries and airplanes to transport these to the war zones?

And then when the cannons are fired and the bombs exploded how much of hot and toxic fumes are released?

Then the energy used to repair roads, houses, water and power supplies, hospitals, schools, would be coming mostly from fossil fuels; dams and windmills, if any, would have been destroyed. Do armed conflicts make any sense to the rest of the world or to the victors themselves when eventually they are affected by the pollution they have created?

Another point: even if the conflict is unarmed, the agri-industrial-commercial strife results in so much waste and environmental pollution.


* Published in print edition on 28 February 2020

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