Viral Infections: How Viruses Spread, Cause Disease and Can Be Prevented

Viruses are very tiny germs: a set of genetic material — either DNA or RNA — inside a protein coating. There are a huge number of them on Earth, but only a small number can infect people. Those that can may cause disease; the common cold, the flu, COVID-19 and HIV are all viral.

How viruses make people sick

Viruses are hijackers. They invade normal, living cells and use them to make copies of themselves, a process called replication. That can kill, damage or change the infected cells, and sometimes the result is illness, from mild to very severe. At other times the immune system fights the virus off and there are no symptoms at all.

Each virus usually infects only one type of cell. Hepatitis viruses attack liver cells, for example, and HIV infects a particular kind of immune system cell.

How they spread

Viruses travel in many ways:

• in droplets and particles breathed out by an infected person, which others breathe in or which land on their mouth, nose or eyes;
• from surfaces or objects carrying the virus, when someone touches them and then their mouth, nose or eyes;
• from a pregnant parent to the baby during pregnancy;
• in contaminated food or water;
• through the bite of an infected insect or animal; and
• through sexual contact — usually vaginal, anal or oral sex — with an infected person.

Treatment

For most viral infections, treatment can only ease the symptoms while the immune system clears the virus. There are antiviral medicines for some viral infections. Antibiotics do not work against viruses.

Prevention

Vaccines can prevent many viral diseases. Everyday habits can prevent others:

• washing hands properly;
• paying attention to food safety;
• cleaning surfaces that may carry germs;
• avoiding contact with wild animals;
• using insect repellent outdoors — and, when traveling somewhere with a high risk of insect-borne disease, wearing long trousers, shirts and socks as well;
• practicing safe sex, with a condom every time for anal, vaginal or oral sex; and
• keeping away from people who are sick.

Sources

Based on "Viral Infections," MedlinePlus, National Library of Medicine; a work of the United States government in the public domain.