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Quick Facts

Overview of Viral Infections


The Manual's Editorial Staff

Last full review/revision Mar 2020| Content last modified Mar 2020
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A virus is a tiny living organism. Viruses are so small they can be seen only with the most powerful microscopes. That's why they're called microorganisms (micro means very small). Other common microorganisms include bacteria. Viruses are much smaller than bacteria.

Unlike bacteria, viruses can't reproduce on their own. So when viruses get into your body, they take over certain cells and use structures in those cells to make more copies of the virus. This usually damages and then kills the cell. However, some viruses can stay inside cells for a long time without killing them.

There are thousands of different viruses. Some viruses infect people. Other viruses infect only animals. Only a few viruses can infect both people and animals.

What is a viral infection?

A viral infection is a sickness caused by a virus.

  • Viruses can get into your body through breathing air, having sex, touching something with viruses on it, or being bitten by a bug such as a mosquito or tick

  • Viruses usually infect only one type of cell—for example, the virus that causes the common cold infects only cells in your nose, mouth, and throat

  • When you get a virus, your white blood cells attack it—these cells also remember how to fight it if the same virus gets into your body again

  • Many viruses make you sick shortly after you get them and then go away

  • Some viruses don't go away and can make you sick a long time after you get them (for example, HIV and herpesvirus)

  • Antibiotics, which treat bacterial infections, can’t treat viral infections

Certain viruses change how your cells work, which can lead to cancer. For example, the hepatitis B and C viruses can lead to liver cancer. HPV (human papillomavirus) can lead to cervical cancer.

How can doctors tell if I have a viral infection?

Doctors can tell if you have certain common viral infections based on your symptoms. They may also do:

  • Blood tests

  • Cultures (when doctors take a sample from your body and try to grow germs from it in a lab)

How do doctors treat viral infections?

Doctors can’t usually do much to treat many viruses. They’ll mainly suggest medicines to treat your symptoms and help you feel better. For example, if you have a stuffy nose, doctors may tell you to take a decongestant.

For some viruses, doctors can give you an antiviral medicine. Antiviral medicines are used for only a few viruses, including:

Antibiotics are drugs that kill bacteria. Antibiotics do not kill viruses.

How can I prevent viral infections?

  • Take good care of your health—for example, wash your hands often with soap and water and practice safe sex

  • Get recommended vaccines

Vaccines are shots that teach your immune system how to fight off certain infections. You usually get vaccines before you're exposed to an infection. But for some viruses, you can get a shot after you're exposed to it. These shots contain antibodies (immunoglobulins) that help fight off the virus. For example, there are immunoglobulin shots for:

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Human Immunodeficiency Virus (HIV) Infection
Human immunodeficiency virus (HIV) infection is a viral infection that progressively destroys certain white blood cells. Untreated, it usually leads to acquired immunodeficiency syndrome (AIDS). Transmission of HIV requires contact with bodily fluid that contains the virus or cells infected with the virus. Which of the following is not a bodily fluid that commonly transmits HIV? 
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