Virus
SARS-CoV-2, a member of the subfamily Coronavirinae
Virus classification
(unranked):	Virus
Realms
Adnaviria Duplodnaviria Monodnaviria Riboviria Ribozyviria Varidnaviria

Structure of tobacco mosaic virus: RNA coiled in a helix of repeating protein sub-units

A virus is a tiny parasite.Virology is the study of viruses.

Viruses can only be seen under an electron microscope. Viruses are not free-living: they can only be parasites. They always reproduce inside other living things. All viruses infect living organisms, and may cause disease. The virus make copies of itself inside another organism's cells. Viruses are a strand of nucleic acid with a protein coat. Usually the nucleic acid is RNA; sometimes it is DNA. Viruses cause many types of diseases, such as polio, ebola and hepatitis.