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Viruses: Facts

What Is A Virus?

Polio

Viruses are in the news. You've certainly heard about COVID-19 and the coronavirus. You may also know about diseases like measles, chicken pox, rabies or polio, and you may have heard of Ebola, West Nile illness, SARS, or AIDS. You've probably heard of the flu, and you've most likely had a "cold" -- your nose is runny, you sneeze a lot, you have a sore throat, and you might feel achy all over. As it turns out, all of these diseases are caused by viruses.

A virus is a microbe, too small to be seen with just your eyes. Other types of microbes are bacteria, protozoa, and fungi. Microbes are all around us. They exist on our skin, in water, on desks and doorknobs, and even in food. Microbes are often called "germs," but not all are harmful. Bacteria, for example, make yogurt, pickles, and cheese, and even break down garbage. Learn more about different types of microbes.

Viruses are different from other kinds of microbes. They are much, much smaller than bacteria. They are so small that 500 million rhinoviruses (which cause the common cold) could fit on the head of a pin. They can only be seen with a powerful electron microscope. Viruses are simple particles made of genetic material (called DNA or RNA) encased in a protective protein coat called a capsid. Some viruses have another coat or shell called an envelope. Take a peek at what's inside a virus.

Sick Boy

Scientists differ about whether viruses are “alive” or not. Most say they are not really “alive” because they lack the characteristics of living things: they are not made of cells, they do not turn food into energy, and they cannot reproduce on their own. They can only multiply inside the cells of other living things such as animals, plants, bacteria or fungi. Most cannot survive long unless they invade a living host. But once they are inside a host cell, they act very much alive.

How Does A Virus Infect You?

Mask

Viruses enter human bodies through the nose, mouth, eyes, or breaks in the skin. They can be passed by coughs, sneezes, insect bites, or even by food or water. Viruses attach to the host cells and get inside them. When a virus infects a cell, its genetic material sends that cell one simple message: Make more viruses! Eventually the virus-filled host cell dies, sending out new viruses to invade more cells of the body.

Viruses follow some basic steps in order to force their host cells to make more viruses. These steps are called the Lytic Cycle.

  1. A virus attaches to a host cell. All viruses have some type of protein on their outside coats that "recognizes" the proper host cell for its type.
  2. The virus, or a virus particle, penetrates the host cell and releases its genetic instructions into the host cell.
  3. The injected genetic material gives instructions to the host cell's enzymes to make parts for more new virus particles.
  4. The new particles assemble the parts into new viruses.
  5. The new virus copies break out of the cell membrane and leave the host cell, ready to infect other cells.
Girl with Scope

Viruses can reproduce quickly and make their host organism sick. You can think of them as microscopic hijackers or pirates: they invade your body, commandeer your cells, and force them to produce the virus. Viruses exist only to reproduce - to make copies of themselves. And they're very good at what they do!

You have probably heard of "computer viruses" and "viral videos." These terms do not refer to real viruses, but to things that spread rapidly like a virus. Computer viruses are a set of instructions that can "infect" its host computer. Viral videos spread quickly around the globe as people use technology to share them.

Immune System to the Rescue!

Nose

Fortunately your body has a defense against viruses. It is called the immune system. If a virus makes it past the barriers your body has - your tough skin, or the sticky mucus and little hairs called cilia lining your breathing tube - then this system takes over.

Here's how it works. The immune system is an organization of different types of cells, tissues and enzymes working together to identify and eliminate all invading substances in your body. Each part of the immune system has its own specialized job. White blood cells are your main defense. They patrol your body. When they come across an antigen, a germ that doesn't belong there, they produce antibodies that work to fight against that particular antigen. Some antibodies destroy antigens while others make it easier for white blood cells to destroy the antigen.

Doctor with Girl

Trillions of white blood cells are hard at work fighting enemy antigens. Sometimes, though, your body needs help from the medicines doctors give you. One of these medicines is called a vaccine. A vaccine is a tiny, weakened, or dead part of a germ that is injected into your body like a medicine. A vaccine is not trying to make you sick. Instead, it's just enough of a germ to get the body's immune system revved up and producing lots of antibodies. So if and when the real germ shows up, there will be lots of antibodies already in place to guard your cells from harm.

What if you do happen to get sick from a virus? Because viruses live inside cells, they are hard to treat with medicine. Antibiotics that treat bacterial infections, such as strep throat or ear infections, do not work on viruses. There are some antiviral medicines that block the entry of a virus into a host cell or interrupt the virus as it attempts to copy itself. But often, only the symptoms of a viral illness can be treated.

That's why it is so important to do everything you can to keep the virus from finding its way into your body. There are many steps you can take to prevent viral infections. Many viruses are passed from infected people to others through the air and through close personal contact. So stay away from people who are sick. Try not to touch your mouth, nose or eyes, so that any germs that might be on your hands won't enter your body. Most important, wash your hands with soap and water for at least 20 seconds, several times throughout the day.

COVID-19

Coronavirus NIAID/RML

In 2020, a new coronavirus called SARS-CoV-2 spread across the globe. The disease known as COVID-19 infected many people in all areas of the world. In order to slow down the spread of the virus, people were asked to maintain distance from each other, and many schools, parks, restaurants, and sports activities were shut down. These actions made it harder for the virus to jump from one person to the next. If the virus can’t spread, fewer people get sick. Scientists are currently working to make a coronavirus vaccine, and others are trying to develop medicines to help those who get sick.

Kids usually don't get very sick from this virus, but you still have a role to play in protecting others. By washing your hands, wearing a face mask in public, and not gathering in crowds, you can help slow the spread of the virus and protect older and sicker people. Stay safe by following the guidelines of scientists and doctors.

Did You Know?

Petri

There are hundreds of different kinds of viruses, and they're constantly changing. It's unlikely that you'll get sick from the same virus twice. That's because the immune system can remember its previous response to a virus attack, and if that foreign substance invades the body again, the immune system gets right to work. Here's a more complete answer to whether you can get sick from the same virus twice.

Plants get viruses, too! Here's an introduction to plant viruses along with some photos.

Is there anything good about viruses? Viruses invade host cells in living organisms, including bacteria. There are some viruses that only infect harmful bacteria cells. These viruses are called bacteriophages, which means "bacteria eaters." These virus phages can be helpful and important. Scientists are studying and finding ways to use phages to infect and destroy harmful types of bacteria that cause disease.

A virologist is a scientist or doctor who does research about viruses. An epidemiologist is a public health expert who studies diseases in populations of people. And a microbiologist is a specialist in the world of tiny, microscopic creatures. Read more about these careers.

Learn more about microbes at Science Trek's Kingdoms of Life page and about your virus-fighting immune system at Science Trek's Blood page.

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