Viruses do not grow or display any nutritional patterns. Their only observable behavior is reproduction and this occurs only within living cells. A virus with RNA is called a retrovirus. Viruses are studied by radiography and use of the electron microscope. They are considered neither prokaryotes nor eukaryotes.
All viruses consist of two basis components the genome and the capsid.
The genome is the core that is either DNA or RNA, but not both. The capsid is a protein shell that protects the genome and makes them resistant to temperature, pH and other environmental factors. The capsid also forms the shape of the virus - helical, icosahedral, and complex symmetry. Viruses gain entrance to the body through the respiratory tract, the gastrointestinal tract or broken skin from an animal bite, mosquito bite or hypodermic needle. After entering the body the virus are selective in the type of body cells that they attack.