What Are Viruses?

You are hearing a lot about viruses as the world deals with its first pandemic in a century. By the time the Spanish flu reached its final peak in 1919, the virus that caused it was still an unknown. By that time, the germ theory was well established and accepted. While bacteria had been observed and were understood to be agents of disease, the concept of a virus hadn't entered anyone's thoughts yet.
A virus differs from bacteria in many ways, the most striking difference being that we can't really classify a virus as a living thing. In all living things, the DNA and RNA in each cell is active. A virus has either DNA or RNA, which is inert. It does not active until the virus enters a host cell. The virus is now a living thing, and now it is feeding off the energy produced by the cell it has infected.
Other differences between a virus and bacteria is that a virus has a protein coat, has only DNA or RNA rather than both, and can transfer its DNA or RNA into other cells. A virus is much smaller than bacteria. Bacteria can be seen with the aid of a light microscope. Viruses are even tinier. They have to be, in order to fit inside a cell.
Most viruses infect only a certain species. Some, like our current coronavirus and the swine and bird flus, are able to make the jump to another species. In the case of the swine flu, it jumped from pigs to people. Because they are structured and behave differently than bacteria, antibiotics used to treat a bacterial infection are no good against viruses. How do we stop viruses then?
Antiviral medications exist, but are difficult to develop. Because a virus uses a host cell to replicate, an effective antiviral has to target only the virus and not the host cell. The most common treatment is to let the virus run its course. Eventually, it is hoped, the immune system will be able to overcome the virus. In the meantime, you're likely to experience some discomfort.
Prevention is your best bet. Vaccinations work to train your immune system to kill a virus by giving it a dead one to work on. Good hygiene like washing your hands (you hear that a lot these days) and avoiding close contact with others help reduce the spread of viruses.
Note: every virus is unique. For information on the current COVID-19 coronovirus, visit the CDC or WHO.
This week's information comes from "Microbiology, an Introduction (8th edition)" by Gerard J. Tortora, Berdell R. Funke, and Christine L. Case; the dreaded Wikipedia antiviral drug entry; and the CDC.