Viral Infections

A virus is a small infectious organism, much smaller than a fungus or bacterium, that must invade a living cell to reproduce (replicate). The virus attaches to a cell (called the host cell), enters it, and releases its DNA or RNA inside the cell. The virus's DNA or RNA is the genetic material containing the information needed to replicate the virus. The virus's genetic material takes control of the cell and forces it to replicate the virus. The infected cell usually dies because the virus keeps it from performing its normal functions. When it dies, the cell releases new viruses, which go on to infect other cells.

Some viruses do not kill the cells they infect but instead alter the cell's functions. Sometimes the infected cell loses control over normal cell division and becomes cancerous. Some viruses leave their genetic material in the host cell, where the material remains dormant for an extended time (latent infection). When the cell is disturbed, the virus may begin replicating again and cause disease.

Viruses usually infect one particular type of cell. For example, cold viruses infect only cells of the upper respiratory tract. Additionally, most viruses infect only a few species of plants or animals. Some infect only people. Many viruses commonly infect infants and children.

Viruses are spread (transmitted) in various ways. Some are swallowed, some are inhaled, and some are spread by the bites of insects and other parasites (for example, mosquitoes and ticks). Some are spread sexually.

The body has a number of defenses against viruses. Physical barriers, such as the skin, discourage easy entry. Infected cells also make interferons, substances that can make uninfected cells more resistant to infection by many viruses.

When a virus enters the body, it triggers the body's immune defenses. These defenses begin with white blood cells, such as lymphocytes and monocytes, which learn to attack and destroy the virus or the cells it has infected.

If the body survives the virus attack, some of the white blood cells remember the invader and are able to respond more quickly and effectively to a subsequent infection by the same virus. This response is called immunity. Immunity can also be produced by getting a vaccine.

Probably the most common viral infections are those of the nose, throat, and upper airways (upper respiratory infections). These infections include sore throat, sinusitis, and the common cold. Influenza is a viral respiratory infection. In small children, viruses also commonly cause croup and inflammation of the windpipe or other airways deeper inside the lungs.

Respiratory infections are more likely to cause severe symptoms in infants, older people, and people with a lung or heart disorder.

The difference between Bacterial and Viral Infections

Simply put, bacterial infections are caused by bacteria and viral infections are caused by viruses. But they're also different in other ways.

Bacteria are single-celled "living" microorganisms that reproduce by dividing. Most bacteria can grow on nonliving surfaces, such as countertops and doorknobs. Not all bacteria are harmful. Some bacteria are even beneficial to your health. But when infectious bacteria enter your body, they can make you sick. Bacteria make toxins that can damage the cells they've invaded. Some bacterial infections, such as strep throat and tuberculosis, are contagious. Others are not.

Unlike bacteria, viruses are not "living" organisms but capsules of genetic material. They require living hosts, such as people, plants or animals, to multiply. Otherwise, they can't survive. When a virus enters your body, it invades some of your cells and takes over the cell machinery, redirecting it to produce the virus. The virus may eventually kill the host cells. Some viral infections, such as influenza and HIV, are contagious. Others are not.

The distinction between bacterial and viral infections is important. Why? Because medications that are effective against one aren't effective against the other.

Bacterial infections are treated with antibacterial antibiotics. Antiviral antibiotics are available for some types of viral infections, but not all. Taking antibacterial antibiotics when you have a viral infection won't treat the viral infection and may even be harmful.

Healthy Trust Immediate Medical Care serves the Chicago North Shore Communities of Lake County, Wheeling, Prospect Heights, Lincolnshire, Deerfield, Buffalo Grove, Northbrook, Highland Park, Long Grove, Riverwoods, Des Plaines, Palatine, Glenview, Highwood, Northfield, Libertyville, Winnetka, Arlington Heights, Mount Prospect, Lake Bluff, Lake Forest, Mundelein, and Bannockburn.