Diane Brown, age 13, of Rockland, I11., for her question:
WHAT IS A VIRUS?
A virus is the smallest and simplest form of life and it is also a major cause of disease. It is a microscopic organism that lives in a cell of another living thing.
Viral diseases in human beings include chicken pox, colds, smallpox, cold sores, hepatitis, influenza, measles, mumps, poliomyelitis and rabies.
Viruses produce disease in an organism by damaging some of its cells, although sometimes they live in cells without harming them.
The human body protects itself from viruses and other harmful substances with an immunity system. White blood cells, called "lymphocytes," provide protection with antibodies, which cover a virus' protein coat and prevent it from attaching itself to the receptors of a cell. Lymphocytes also destroy cells that have been infected by viruses.
Scientists consider viruses to be so primitive that they can be called both living and nonliving things. By itself, a virus is a lifeless particle that cannot reproduce. But inside a living cell, a virus can become an active organism that can multiply hundreds of times.
Most viruses can be seen only with an electron microscope. The largest virus is about one tenth as big as a bacterium of average size. A bacterium is from one to 10 micrometers in size. A single micrometer measures only one twenty five hundredth of an inch (1/25,000).
Martinus Beijerinck, a Dutch botanist, started studying viruses in 1898 when he discovered something smaller than bacteria could cause disease. He named the particle "virus" after the Latin word meaning "poison."
Work by an American biochemist Wendell Stanley in 1935 eventually led to the development, during the 1950s, of vaccines for measles, poliomyelitis and other virus caused diseases.
Unlike other organisms, viruses are not made up of cells: Therefore, they lack some of the substances needed to live on their own. They must enter a cell of another living thing in order to obtain these substances. They can then use the cell's materials to live and reproduce.
There is as yet no completely satisfactory treatment for a virus caused disease because drugs able to kill or damage the virus might also damage healthy cells.
Doctors today can definitely treat patients with symptoms of viral diseases. Only the body's immune system, however, can actually fight the viruses themselves. A doctor might give aspirin to bring down a high fever.
But the best way to deal with viruses is vaccination before a viral disease strikes. Vaccination causes the body to produce antibodies that resist a virus when it enters the body.