Viral infection: Infection caused by the presence of a virus in the body. Depending on the virus and the person's state of health, various viruses can infect almost any type of body tissue, from the brain to the skin. Viral infections cannot be treated with antibiotics; in fact, in some cases the use of antibiotics makes the infection worse. The vast majority of human viral infections can be effectively fought by the body's own immune system, with a little help in the form of proper diet, hydration, and rest.

Common viral infections may be diagnosed based on symptoms. For infections that occur in epidemics (such as influenza), the presence of other similar cases may help doctors identify a particular infection. For other infections, blood tests and cultures (growing microorganisms in the laboratory from samples of blood, body fluid, or other material taken from an infected area) may be done. Blood may be tested for antibodies to viruses or for antigens (proteins on or in viruses that trigger the body's defenses).

Viral infections are hard to treat because viruses live inside your body's cells. They are "protected" from medicines, which usually move through your bloodstream. Antibiotics do not work for viral infections. There are a few antiviral medicines available. Vaccines can help prevent you from getting many viral diseases.

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.

Viral infections are caused by the virus. The virus enters the body through swallowing, inhalation, infected food, transfer from human to human contact, or transfer from insect bites. The instant the virus has entered the body, the immune system immediately tries to rid the alien particle from the system. Sometimes the immune system wins and sometimes the virus begins to attach itself to an available cell.

Viral infections in small children can be more difficult to deal with simply because children tend to be cranky when they are ill. Soothing their symptoms as they arise can help them cope with the illness. Adults who contract viral infections should listen to their body. Sleeping as needed and drinking ample fluids can help the body fight off the viral infection faster. Viral infections should be diagnosed by a physician.

Rotaviruses are a group of viruses that can cause severe viral gastroenteritis in infants and young children. They cause about half of all hospitalised cases of gastroenteritis in children less than five years of age. In temperate climates, ...

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.

Viral infections can produce inflammation of the meninges (causing viral meningitis), the brain (causing viral encephalitis), the spinal cord (causing myelitis), or spinal nerve roots (causing shingles). Viral encephalitis is often accompanied by viral meningitis. Viral encephalitis is more serious because it directly affects the brain rather than the meninges.

Some viral infections are mild, causing fever and a general feeling of illness (malaise), often without specific symptoms. Usually, viral meningitis produces symptoms that are similar to those of bacterial meningitis (fever, headache, vomiting, weakness, and a stiff neck) but that are much less severe.

Yellow fever is a serious viral disease transmitted by mosquitoes in parts of Africa and South America. Vaccination is a legal requirement for people travelling through infected areas.