Overview of Viral Infections

Reviewed/Revised Feb 2024

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What is a viral infection?|
How can doctors tell if I have a viral infection?|
How do doctors treat viral infections?|
How can I prevent viral infections?|

A virus is a microorganism, a tiny living organism. Other common microorganisms include bacteria. Viruses are much smaller than bacteria and can be seen only with the most powerful microscopes.

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 (for example, the virus that causes COVID-19), 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.

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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