From SARS to Coronavirus: A Comparative Study of Viral Pandemics

How do viruses work? The answer to that question might be complex, but it is not something that we can afford to overlook. A virus is a microscopic parasite that cannot reproduce without a host cell. This means that it needs to enter a living organism, hijack its cellular machinery, and commandeer its mechanisms for reproduction. Sounds daunting? That's because it is. Not only can viruses infect humans, but they can also infect animals, plants, and even bacteria.

In recent times, viruses have ended up in the spotlight due to the COVID-19 pandemic. While the world collectively suffers from the effects of this virus, it is important to have a basic understanding of what viruses are and how they work. In this article, we will explore the workings of viruses and learn about some examples of how they have affected humanity throughout history.

The basics of viruses

Viruses are not alive in the traditional sense; they are acellular, which means that they lack a cell membrane and typical cellular organelles. They are essentially just a strand of genetic material, either RNA or DNA, wrapped in a coat of protein. These tiny structures are hardly visible under a microscope, and yet they can wreak havoc in a massive way. To understand how they work, we need to break down the virus structure and look at their methods of transmission.

Infecting host cells

Viruses require a host cell to reproduce, and they do this by hijacking the host's cellular machinery. The virus attaches itself to the host cell using specific protein molecules present on both the virus and the cell's surface, which allows the virus to enter the cell. Once inside, the virus will then use its genetic material to take over the host cell and force it to produce the proteins it needs for replication.

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This method of replication enables the virus to produce millions of copies of itself within the host cell, ultimately leading to the death of the host cell. Once enough virus copies are created, they burst out of the cells and infect other cells in the body, continuing the replication cycle and causing damage to the host organism.

Methods of transmission

We know that viruses infect host cells, but how do we come into contact with viruses in the first place? Viruses have several methods of transmission, including:

Airborne transmission – some viruses, like the flu, are carried in the air, and we can inhale them when an infected person coughs or sneezes.

Food and water – some viruses, like the norovirus, can be present in food or water and can enter our bodies that way.

Direct contact - viruses like the cold sore virus or herpes simplex virus can be transmitted from person-to-person through direct contact.

Vector-borne transmission - this type of transmission occurs where an insect or animal acts as an intermediary carrier. The Zika virus, for example, is carried by mosquitoes.

Some viruses, like SARS-CoV-2 (the virus responsible for COVID-19), can be transmitted through any of the above methods. This is why contact tracing, social distancing, and mask wearing are so important during a pandemic.

Historical examples of viruses

Throughout history, viruses have caused pandemics that have affected human populations on a large scale. Here are a few examples:

Spanish flu

One of the deadliest pandemics in history, the Spanish flu, occurred in 1918 and affected around 500 million people worldwide. The virus is estimated to have killed between 20 and 50 million people. The Spanish flu was caused by the H1N1 virus and had a much higher mortality rate than the usual flu that we are accustomed to. While the Spanish flu pandemic was over a century ago, its impact on the world remains significant, and our scientific understanding of it continues to inform our response to pandemics today.

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HIV, the virus that causes AIDS, made its appearance in the 1980s, and it has since affected millions of people worldwide. HIV is transmitted through bodily fluids like semen, vaginal fluids, blood, and breast milk. Without treatment, the virus attacks the immune system and can lead to AIDS, which compromises the body's ability to defend against infection and disease.


The Ebola virus first appeared in 1976 and caused a number of outbreaks in West Africa. This virus is transmitted through contact with bodily fluids and can cause internal and external bleeding, as well as fever and muscle pain. The Ebola virus has a mortality rate of 50% and can also cause long-term effects such as joint pain, headache, and vision loss.


In summary, viruses are tiny structures that can cause havoc on a large scale. They require a host cell to reproduce, and they can use various methods of transmission to infect new hosts. While we have explored several examples of viruses, our understanding of viruses is continuously evolving, and the science of virology remains an essential part of our understanding of the world. As the world faces new pandemics and viruses, it is all the more necessary to understand the basics of viruses and their workings.

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