Coronavirus, a species in the genera of animal virus, belongs to the subfamily Coronavirinae in the family Coronaviridae. They are enveloped viruses with single-stranded RNA genome and a helical symmetry. The genome size ranges from 16 to 31 kilobases. The name, meaning crown, comes from the virus envelope appearing to be crowned when viewed under an electron microscopy.

These viruses mainly infect the upper respiratory system and the gastrointestinal tract of mammals and birds. There are four to five different coronaviruses that infect humans. SARS-CoV which causes SARS causes both upper and lower respiratory tract infections and can also cause gastroenteritis. Coronaviruses can lead to a significant percentage of all common colds. Unlike rhinoviruses the human coronaviruses are difficult to grow in the laboratory.

Coronaviruses cause a range of diseases in farm animals and domesticated pets which can sometimes be serious. Many animals are infected with coronaviruses including bovines, canines, felines, porcine, and mice. MHV was the most studied cornoavirus prior to SARS CoV.

When the coronavirus enters the cell in the cytoplasm replication starts. The coronavirus has a polyadenylated-A tail to make it resemble its RNA host as much as possible.

SARS-CoV, a novel coronavirus, was discovered in 2003 after an outbreak in Asia spread worldwide the next year. It resulted in over 8000 infections and around 10% of those resulted in death. Due to the publicity that the SARS outbreak received a renewed interest in coronaviruses has happened. For a long time only two coronaviruses were known; however, by the end of 2004 a fourth human virus was discovered. Its name is the New Haven coronavirus, although that name is still contested by the three labs that discovered it. A team in Hong Kong found and named a fifth coronavirus.