virus

A virus is a small infectious agent made of genetic material, either DNA or RNA, enclosed within a protective protein coat. Viruses cannot reproduce independently and must enter living CELLS of a host organism to replicate. During INFECTION, a virus attaches to a host cell, introduces its genetic material, and uses the cell's biological machinery to produce new viruses. Viruses infect humans, animals, plants, and microorganisms and can cause many diseases, including INFLUENZA, CHICKENPOX, POLIOMYELITIS, and infections caused by RETROVIRUSES.

A virus is a tiny infectious agent that enters living cells and uses them to make more copies of itself.

• Microscopic infectious agent • Requires living host cells to multiply • Contains DNA or RNA genetic material • Can infect humans, animals, plants, and microorganisms • Causes many infectious diseases • Different viruses are classified by structure and genetic material