*A virus is a neucleoprotein that multiplies only in a living cells and have the ability to cause disease. It's too small to be seen with unaided eye and even with a light microscope🔬.
*All viruses parasitize cells and cause a multitude of diseases in all forms of living organisms. Some viruses attack human, animals or both and causes diseases such as influenza, polio, rabies, small pot, HIV, AIDS etc.
*known virus exceed 2000 and new ones are discovered almost every month.
*one virus may infect one or dozens of different species of plants and animals.
*more than one virus may infect a plant and animal.
*Although viruses behave like a microorganism because they have genetic function and are able to replicate and cause a disease. They also behave like a chemical molecules.
*At there simplest they consist of nucleic acid and protein.
Note: nucleic acid is the effective portion & protein is a protective coat around the nucleic acid.
*Although viruses can take any of several forms they are mostly rodshaped, polyhedral(isosohedral) or varieties of the two basic structures.
*In virus there is only RNA or DNA.
- Virulence is used to measure the degree of damage of a virus