The Coronovirus belongs to a family of viruses, Coronaviridae, that include over a dozen major host-specifc pathogens of mammals and birds. They can infect the respiratory tract (avain infectious bronchitis), the gut (transmissible gastroenteritis virus in pigs), or the liver and brain (hepatitis virus in mice). The coronaviruses are so named because the viral particle resembles a solar corona. The virion can range in size form 60nm to 220nm with a genome of positive polarity ssRNA.

Until the recent outbreak of SARS, there was no link between human coronaviruses and serious disease affecting humans. Hovever, coronaviruses are linked as a causative agent of the common cold. Two genera within the Coronaviridae, previous to SARS, Coronavirus and Torovirus, can infect humans. The genus Coronavirus includes two human serotypes causing respiratory diseases, Human Coronavirus (HCV)-229E and HCV-OC43. Uning a technigue called Enzyme Immunoassay (EIA), they can be identified in the laboratory from nasopharyngeal aspirates or nasal swabs. For these serotypes, the virus infects and remains localized in the epithelium of the upper respiratory tract causing nasal discharge, sore throat, with little of no fever.

Scientists have detected a previously unrecognized Coronavirus in patients with SARS. The new Coronavirus is the leading hypothesis for the cause of SARS, however, other viruses are still under investigation as potential causes In general, SARS begins with a fever greater than 100.4°F [>38.0°C]. Other symptoms may include headache, an overall feeling of discomfort, and body aches. Some people also experience mild respiratory symptoms. After 2 to 7 days, SARS patients may develop a dry cough and have trouble breathing. SARS can be a lethal disease. Since the viral genome has been sequenced, the Coronavirus purported to cause SARS can be identified using nucleic acid probes.