Respiratory virus screen at Oxford, The Manor Hospital

Viruses are very tiny, infectious agents that multiply inside living cells. They are so small that most can only be seen using an electron microscope. Their sole activity is to invade cells of living organisms; where they take over to make copies of themselves. All viruses have the same basic structure, but their shape or size may vary. Unlike bacteria, viruses cannot be grown in culture and antibiotics are not an effective treatment against them.

Anti-viral drugs are now available. These work by either preventing viruses from entering a cell or by altering their ability of the virus to multiply. 

Viruses can cause disease in a variety of ways:

• They may destroy or disrupt the activity of the cells they invade which can affect vital organs.
• Your body’s immune system response to a virus may lead to symptoms such as fever and fatigue.
• Interactions with areas of the host cell - i.e. viruses have been implicated in causing cancer.
• Viruses may cause disease by weakening the body’s immune system allowing other illnesses to develop - as in AIDS.

Your body’s defence to virus invasion is fairly rapid. However a virus can hide from the immune system allowing the infection to recur or become chronic.