Viral Infections

Source: MedlinePlus Health Topics, U.S. National Library of Medicine

Last synced 8/7/2026Status: primary verified

What are viruses? Viruses are very tiny germs. They are made of genetic material (either DNA or RNA) inside of a protein coating. There are a huge number of viruses on earth. Only a small number of them can infect humans. Those viruses can infect our cells, which may cause disease. Some of the diseases that viruses can cause include the common cold , the flu , COVID-19 , and HIV . How are viruses spread? Viruses can be spread in different ways: Through droplets and particles that are breathed out by someone who has the infection. You might breathe in the droplets or particles, or they could land on your mouth, nose, or eyes. By touching surfaces or objects that have the virus on them and then touching your mouth, nose, or eyes. From the pregnant parent to the baby during pregnancy . Through contaminated food or water . By being bitten by an infected insect or animal. Through sexual contact (usually vaginal, anal and oral sex) with someone who has the infection. How do viruses cause disease? Viruses are like hijackers. They invade living, normal cells. They then use those cells to multiply (make copies of themselves). This process is also called replication. The process can kill, damage, or change the infected cells. Sometimes this can make you sick. The symptoms can range from mild to very severe. Other times, your immune system may be able to fight it off and you may not have any symptoms. Each different virus usually only infects one type of cell in your body. For example, hepatitis viruses affect the cells in the liver. HIV infects a certain type of immune system cell. What are the treatments for viral infections? For most viral infections, treatments can only help with symptoms while you wait for your immune system to fight off the virus. There are antiviral medicines to treat some viral infections. Antibiotics do not work for viral infections. Can viral infections be prevented? Vaccines can help prevent you from getting many viral diseases. You may be able to p

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This information is for general education and is not medical advice. Always talk to a licensed U.S. clinician about your situation, medications, or treatment decisions.