The SARS-COV2 Virus
Covid-19 infection is caused by the SARS-COV2 virus. SARS stands for Severe Acute Respiratory Syndrome. (Petrosillo et al., 2020 doi: 10.1016/j.cmi.2020.03.026)
Viruses aren't technically alive. They don't make its own energy and must hijack the machinery inside living cells to replicate.
Viruses consist of a core of genetic material, either DNA or RNA, with a protein coat. On this they have several proteins. Some of these can be used to bind to and enter cells. Some viruses may also have an envelope surrounding them made from fats.
(Medical Microbiology 4th Edition, 1996, Hans R. Gelderblom)
The word corona means crown and refers to the appearance that coronaviruses get from the spike proteins sticking out of them. SARS-COV2 uses its proteins to bind the ACE2 protein on our cells, so that it can infect them. The ACE2 receptor is found on cells throughout our body: in the mucosa lining the nose and mouth, the throat, lung, stomach, small intestine, colon, skin, lymph nodes, thymus, bone marrow, spleen, liver, kidney, and brain.
(cdc.gov/coronavirus/2019-ncov/your-health/about-covid-19/basics-covid-19.html; Hamming et al., 2004 doi: 10.1002/path.1570)
Viruses Related to SARS-COV2
Currently, there are seven known Human Coronaviruses. Four are endemic and considered partly responsible for the common cold. Two are more severe: SARS-COV (often referred to as SARS) and MERS-COV (often referred to as MERS). The closest relative to SARS-COV2 is SARS-COV (SARS). (Cui et al., 2019 doi: 10.1038/s41579-018-0118-9; Tabibzadeh et al., 2020 doi: 10.1002/vms3.394)
SARS emerged in 2002 in China, resulting in an outbreak where cases were recorded in countries around the world. Symptoms included fever, cough, shortness of breath, sore throat, diarrhea and vomiting. Laboratory findings for patients admitted to hospital also showed low numbers of white blood cells (cells that fight infection) and platelets (cells that help blood clot).
In total, over 8000 people were infected and the virus showed a mortality rate of 11%. Of those that survived, many experienced long term symptoms with reports of reduced lung function and exercise capacity and an frequently an inability to return to work. (Petrosillo et al., 2020 doi: 10.1016/j.cmi.2020.03.026; cdc.gov/about/history/sars/timeline.htm; Chan-Yeung and Xu 2003 doi: 10.1046/j.1440-1843.2003.00518.x; Ngai et al., 2010 doi: 10.1111/j.1440-1843.2010.01720.x)