Page 12 - Dream May 2020 English

COVID-19 SPECIAL
CAUSATIVE AGENT
Pandemic COVID-19
– First or last?
Arvind c. Ranade
There is worldwide concern about the ongoing COVID-19 pandemic, which has already spread over more than 210 countries and infected 16,05,732 people across the world. One may wonder why there is such a huge public outcry this time when viruses have been around us for ages. Is the COVID-19 pandemic the first or will it be the last of its kind?
of ‘spontaneous generation’. French scientist Louis Pasteur demonstrated that diseases were caused by microscopic organisms. While obtaining microorganism-free filtered water for experiments, Charles Edouard Chamberland, one of Louis Pasteur’s assistants, developed a Pasteur-Chamberland filter. This invention was also used in restaurants and homes in America and Europe to obtain bacteria-free drinking water,
thereby reducing the bacterial infections.
To find out the causative agent that damage tobacco plants, Ivanovsky filtered the crushed leafs of infected tobacco plant. If the disease-causing agents were a bacteria, then the filtered liquid should have been devoid of it. Yet the filtered liquid could cause ravage in the tobacco plant. Hence it was not a bacteria but something else.
Soon, it was realised that viruses are not limited to plants, but they plunder animals and bacteria as well! Today we know that the size of viruses range from 20 to 400 nm (nanometre). Typically, a human cell is a thousand times bigger than the virus. As of today, thousands of different viral species have been studied and described by scientists, and millions more are likely to be present in nature.
Viruses come in various sizes and shapes, but all species consist of a small collection of genes, i.e., stretches of either deoxyribonucleic acid (DNA) or ribonucleic acid (RNA), which carry information for making more copies of the virus. These genes are enclosed in a protective coating of protein and someti mes a lipid membrane. All known viruses are parasitic, each having
its own preferred host to infect. Some target plant cells, some only infect bacteria, a few live in bats and some infect humans.
A cursory glance at history would show several pandemic diseases originating from viruses that had plagued the humankind in the past. For example, in 1918, Spanish Influenza, also known as the Spanish Flu, devastated millions of people around the world. The Acquired Immuno Deficiency Syndrome (AIDS), which appeared in 1983, is another viral disease caused by the Human Immuno Deficiency virus (HIV) spilled over from chimpanzees. The H1N1 Swine Flu of 2009 came partly from pigs. It is also considered to be evolved through a recombination with a pig virus and a bird virus, which is still awaiting conclusive evidence. Hendra, Ebola and Hanta are a few other viral diseases in the list.
A virus is so small that it
takes the magnifying power of an
electron microscope to become
visible. The electron microscope
was invented only in the 1930s.
However, existence of virus and
its effects were discovered much
before that. For example, in
1892, Russian botanist Dmitry
Ivanovsky discovered the Tobacco
Mosaic Virus (TMV) that caused
havoc in tobacco plants. Here
it is important to mention that
Ivanovsky was not sure whether
it was really a new species or
kind of bacteria only or a virus. Therefore, he made use of the pasteurization process based on repudiating the theory
Typical virus structure
Typical virus structure in comparison with Influenza virus
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