Virus

A virus is a small infectious agent that replicates  only inside the living cells of other Organisms. Viruses can infect all types of life forms, from animals and plants to microorganism's, including bacteria and archae Viruses spread in many ways; viruses in plants are often transmitted from plant to plant by insects that feed on plant sap is, such as aphids; viruses in animals can be carried by blood-thirsty insects. These disease-bearing organisms are known as vectors.Viral infections in animals provoke an imminent responses that usually eliminates the infecting virus. Immune responses can also be produced by vaccine, which confer an artificiality acquired Immunity to the specific viral infection. In the early 20th century, the English bacteriologist Frederick twort discovered a group of viruses that infect bacteria, now called bacteriophages the first images of viruses were obtained upon the invention of electron microscope in 1931 by the German engineers ErnstRuskaan and Maxa knoll