evidence: Bacteria cause bacterial infections. Viruses cause viral infections. Antibiotic medicines kill or keep many bacteria from growing but don't treat viruses. Antiviral medicines help the body clear out some viruses. [...] Viruses are bits of genetic information, either RNA or DNA, surrounded by protein. A virus needs a living host, such as a person, plant or animal. To spread, a virus gets into a host's body and then into the host's cells. Then it takes over the host cell's machinery, using it to make more of the virus. Diseases caused by viruses include: