A virus is a small infectious organism—much smaller than a fungus or bacterium—that must invade a living cell to reproduce (replicate). The virus attaches to a cell (called the host cell), enters the cell, and releases its DNA or RNA inside the cell. The virus’s DNA or RNA is the genetic material containing the information needed to make copies of (replicate) the virus. The virus’s genetic material takes control of the cell and forces it to replicate the virus. The infected cell usually dies because the virus keeps it from performing its normal functions. When it dies, the cell releases new viruses, which go on to infect other cells. Viruses are classified as DNA viruses or RNA viruses, depending on whether they use DNA or RNA to replicate.
Coronaviruses are a family of RNA viruses that infect and cause disease in mammals and birds. In humans they typically cause upper respiratory infections that can range from mild to fatal.
Coronaviruses constitute the subfamily Orthocoronavirinae, in the family Coronaviridae. They have characteristic club-shaped spikes that project from their surface, which in electron micrographs create an image reminiscent of the stellar corona, from which their name derives.
Alphacoronaviruses and betacoronaviruses infect mammals, while gammacoronaviruses and deltacoronaviruses primarily infect birds.
Betacoronaviruses (β-CoVs or Beta-CoVs) are one of four distinct genera of coronavirus. Member viruses are enveloped, positive-strand RNA viruses that infect mammals (including humans). The natural reservoir for betacoronaviruses are bats and rodents. Rodents are the reservoir for the subgenus Embecovirus, while bats are the reservoir for the other subgenera.
Each coronavirus genera are composed of various viral lineages with the betacoronavirus genus containing four such lineages: A, B, C, and D.
Severe acute respiratory syndrome-related coronaviruses (SARS-CoV) are a species of coronavirus (family Coronaviridae) within the genus Betacoronavirus and the subgenus Sarbecovirus (ie. SARS Betacoronavirus). Bats serve as the main host reservoir species for the SARS-related coronaviruses. While SARS-coronaviruses have evolved in bats for thousands of years, they have only recently evolved to be able to jump into other species, including humans.
There have been two strains of SARS-CoV that have infected humans, and both have caused significant outbreaks.
Severe acute respiratory syndrome coronavirus 1 is a SARS-related coronavirus that is responsible for causing the disease SARS (Severe Acute Respiratory Syndrome). It is the virus responsible for the SARS outbreak in 2002-2004 which affected thousands across the globe and resulted in over 750 deaths worldwide.
Severe acute respiratory syndrome coronavirus 2 is a SARS-related coronavirus that causes the disease COVID-19 (coronavirus disease 2019), which was first discovered in Wuhan, China in late 2019 and within weeks of its identification spread across the globe, causing the worst pandemic in modern history.
