Imagine something that doesn’t grow or eat, yet reproduces. This something is a virus. A virus is nonliving and consists of a core of hereditary material surrounded by a protein coat. Viruses are so small that scientists must use extremely powerful microscopes to see them.

Viruses are unlike living things. They can reproduce only inside a living cell. Some viruses can be made into crystals and stored in a jar on a shelf for years. Then, if they enter an organism, they may quickly reproduce. This may cause new infections and damage the organism. Viruses, therefore, have the potential to greatly impact the living world.

When most people hear the word virus, they relate it to a cold sore, a cold, or HIV, the virus that causes AIDS. Mumps, measles, and chicken pox are also diseases caused by viruses. A virus must be inside a living cell to reproduce. The cell in which a virus reproduces is called a host cell. Once a virus is in a host cell, the virus can act in two ways. It can either be active or it can become latent, an inactive stage.

Active Viruses

When a virus enters a cell and is active, it causes the host cell to make new viruses, which destroy the host cell.

Latent Viruses

Some viruses may be latent viruses. A latent virus a cell and its hereditary material may become part of the cell’s hereditary material. It does not immediately destroy the cell or make new viruses. Latent viruses may appear to hide inside host cells for many years. Then, at any time, the virus can become active. Stress, or too much sun or cold, may cause a virus to become active.

Viruses may cause diseases in plants, animals, fungi, bacteria, and protists. There are no antibiotic medications to cure viral diseases. But some viral diseases can be prevented by vaccines. A vaccine is made from damaged virus particles that can’t cause disease anymore.