Do you often get colds and flu? Or do you get stomach aches and diarrhea? Behind many of these things that make us sick is a tiny enemy that we cannot see. We call these people "viruses." So, who are these viruses? How do they get into our bodies and make us sick? Today, we will talk about all this very simply, in a way that you can understand.
Simply put, what is a virus?
A virus is a very small germ (pathogen) that we cannot see with our eyes. They can infect not only humans, animals, and plants, but also bacteria and fungi. However, a single virus can only infect a specific type of host.
A virus is like a little piece of information wrapped in a little "bag." This bag is called a protective covering made of protein, called a ``capsid.'' Unlike the cells in our body, viruses cannot divide and make copies of themselves on their own. Instead, they infiltrate a cell in our body and use the resources and machinery of that cell to make thousands of copies of themselves.
Imagine this. Someone sneaks into your kitchen. They bring their own recipe, but they use your pots, pans, spoons, blender, oven, everything to make the food. A virus does exactly the same thing. The virus enters one of our cells, uses the contents of that cell to make many copies of itself. Eventually, it destroys that cell, then comes out and infects other cells.
What are the main characteristics of a virus?
Viruses have several common characteristics. Let's see what they are.
| Feature | Simple explanation |
|---|---|
| Genetic Material | A virus is made up of genetic information. This can be RNA or DNA. This information is contained within a protective protein coat (capsid). |
| Envelope | Some viruses have another fatty coating outside the capsid. We call this an 'envelope'. Viruses without this type of coating are called "naked viruses". |
| Parasitic Nature | Viruses are like parasites. They cannot live or reproduce on their own. They absolutely need another living cell (a host cell) to do so. |
| Very small size | Viruses are particles that are 100 to 1000 times smaller than a cell in our body. They cannot be seen with a regular microscope, they require an electron microscope. |
What types of viruses do we hear about most often?
There are thousands of types of viruses. They are divided into different groups based on their shape, size, and genetic material. Let's look at a few types of viruses that we often hear about and that are important to us.
- Influenza viruses: These are what cause the common cold and flu. Viruses in this family are also responsible for things like bird flu and swine flu.
- Human herpesviruses: This is a large family of viruses. These viruses cause a variety of diseases, including cold sores, genital herpes, chickenpox, and shingles.
- Coronaviruses: The COVID-19 disease that has recently paralyzed the world is caused by a virus from this family. However, there are also types of coronaviruses that cause the common cold.
- Human papillomaviruses (HPV): These viruses cause warts on the skin. Some types of HPV can also cause cancers such as cervical cancer.
- Hepatitis viruses: These are viruses that infect our liver. Hepatitis A, B, and C are the main types.
- Retroviruses: These are RNA viruses. The HIV virus belongs to this group. These viruses can insert their genetic information into our own DNA.
Some viruses also have the ability to cause cancer. We call them oncoviruses. HPV, hepatitis B and C, and HIV are some of these viruses.
How do viruses enter our bodies?
Viruses are like thieves, they look for openings to enter our bodies. They mainly enter through the mucous membranes of our eyes, nose, mouth, and genitals. That means:
- By inhaling droplets from an infected person when they cough or sneeze.
- By touching a surface contaminated with the virus and then touching your eyes, nose, or mouth with the same hand.
- Having unprotected sex with someone who is infected.
- By ingesting infected blood.
Viruses can also enter the body through a skin wound, scratch, or bite from an animal such as a mosquito or tick (e.g. dengue, Zika).
What do viruses do after entering the body?
The process by which a virus infects our cells is very complex. It can occur in two main cycles.
1. Lytic Cycle
This is the active, fast method.
- Attachment and entry: The virus attaches to the surface of one of our cells. It then tricks the cell into entering.
- Replicating: Once inside a cell, the virus takes control of the cell. It then uses the cell's resources to make thousands of copies of its genetic material and protein coats.
- Assembly: Newly formed parts come together to form completely new virus particles.
- Release: The number of viruses inside the cell increases, and eventually the cell bursts. Thousands of new viruses then come out and start infecting healthy cells around them. This is what happens in diseases like the common cold and influenza.
2. Lysogenic Cycle
This is a silent, hidden method.
- After some viruses enter a cell, they do not destroy it. Instead, the virus integrates its genetic information (DNA) into the cell's DNA.
- Now, when the cell divides normally, each new cell inherits that piece of DNA from the virus. The cell doesn't even know the virus is there.
- In this way, the virus can remain hidden in the body for years, without causing any symptoms.
- However, for some reason (e.g. stress, illness and weakened immunity), this silent virus can suddenly become active. Then it switches to the lytic cycle and begins to infect cells by destroying them. The herpes virus that causes blisters in the mouth, and herpes zoster ``(shingles)`` that occurs after chickenpox are good examples of this.
Are viruses alive or not?
This is a bit of a complicated issue. There are different opinions about this among scientists. Generally, to be called an organism, it must be able to produce energy on its own (metabolism) and reproduce on its own. A virus cannot do both. It definitely needs another cell. That's why many people say that viruses are lifeless .
However, they can reproduce inside a cell and evolve over time, which is why some say they are in between life and non-life.
What are the common diseases caused by viruses?
Viruses are the cause of many of the diseases we face in our daily lives. Some examples are:
- Common cold
- Influenza (flu)
- COVID-19
- Dengue
- Chickenpox
- Measles
- Mumps
- Polio
- HIV/AIDS
- Genital warts and cervical cancer (HPV)
- Genital Herpes
- Rabies
- Hepatitis (liver inflammation)
Viruses are a part of our world. While some of them can make us sick, scientists believe that there are trillions of viruses that live inside our bodies without causing any harm. The most important thing is to follow the necessary hygiene habits and seek medical advice at the right time to protect yourself from viruses that can cause illness.
Take-Home Message
- Viruses are tiny germs that cannot survive on their own and require cells in our body to reproduce.
- They can be spread through the air, touch, body fluids, and insect bites.
- The best way to protect yourself from viral infections is to practice good hygiene, such as washing your hands frequently with soap and water .
- Vaccination is a very effective way to protect against many dangerous viral diseases.
- If you have symptoms of a viral infection (fever, body aches, cough, chills), it is important to get plenty of rest and see your doctor for proper advice.
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