Viruses are simpler and smaller organisms than bacteria and are less able to sustain themselves. These organisms can survive and multiply only by penetrating body cells. In order to reproduce, a virus requires a living cell. The invaded cell eventually dies and the new viruses are released, spreading and infecting other cells. Because viruses perform few functions independently, medicines that disrupt or halt their life cycle without harming human cells have been difficult to develop.
There are many different types of virus, and viral infections cause illnesses with various symptoms and degrees of severity. Common viral illnesses include colds, influenza and flu-like illnesses,' cold sores and childhood diseases such as chickenpox and mumps. Throat infections, pneumonia, acute bronchitis, gastroenteritis and meningitis are often, but not always, caused by a virus.
Fortunately, the body's natural defences are usually strong enough to overcome infections such as these, with drugs given to ease pain and bring down fever. However, the more serious viral diseases, such as pneumonia and meningitis, need close medical supervision. Another difficulty with viral infections is the speed with which the virus multiplies. By the time symptoms appear, the viruses are so numerous that anti-viral drugs have little effect. Anti-viral agents must be given early in the course of the infection; they may also be used as a prophylactic (preventive). Some viral infections can be prevented by vaccination.
Friday, May 25, 2007