What is COVID-19?

Background

COVID-19 is a positive sense RNA virus. In simpler terms, this means that the COVID-19 genome can provide instructions to a human cell to make viral proteins. Most viruses in the world, ranging in severity from anything from rhinoviruses that cause the common cold to Hepatitis C, are positive sense RNA viruses.

COVID-19 falls within the family of coronaviruses, which are named as such because they look like a solar corona under electron microscopy. Some coronaviruses cause cold-like symptoms, such as fever, sore throat, and swollen lymph nodes. There are several strains of coronavirus that lead to severe respiratory distress, which include the 2003 SARS and 2012 MERS variants, which have led to epidemics with high mortality.

Electron microscope image of the Novel Coronavirus
Electron microscope image of coronavirus.
Credit: NIH/AP/Shutterstock
Image of a solar corona.
Credit: Shutterstock

COVID-19 and SARS-CoV-2

SARS-CoV-2 is the technical name for the coronavirus that is the cause of the current pandemic. COVID-19 is the name of infectious disease caused by SARS-CoV-2.

We are still learning about this disease, and I will update these posts as I too learn more, but we know that there is a widespread presentation of symptoms for people infected with this disease. Some are asymptomatic, while others progress to pneumonia, respiratory failure and death.

SARS-CoV-2 emerging from a human cell
Scanning electron microscope image of SARS-CoV-2.
Source: NIAID-RML
More images at: https://www.flickr.com/photos/niaid/albums/72157712914621487

SARS-CoV-2 Infects Humans through ACE2 Receptors

SARS-CoV-2 binds to angiotensin-converting enzyme 2 receptor (ACE2), which is the same receptor used by the SARS virus in 2003. This receptor is present on lung alveolar cells, enterocytes in the small intestine, and also blood vessels and organs throughout the body (Hamming et al. 2004 https://onlinelibrary.wiley.com/doi/full/10.1002/path.1570)

Hamming describes that ACE2 receptor are on type II alveolar cells, which are responsible for repair of damaged lung tissue and may also be the reason why SARS-CoV-2 rapidly expands in a human.

Moreover, ACE2 receptors are found in small intestine, which is why some patients have diarrhea and why we can detect the virus in the stool. This is also why some people think our current pandemic may spread from sharing food with other people The most concerning fact is that ACE2 receptors are on endothelium and smooth muscle cells of virtually every organ, which may be why we see kidney failure, myocarditis, or multi-organ failure in COVID-19.

Yan et al. recently discovered the spike glycoprotein is the key for how the virus enters ACE2 receptors. https://science.sciencemag.org/content/early/2020/03/03/science.abb2762

Pharmaceutical companies are looking to create antibodies against the spike protein or against the ACE2 receptor to prevent further infection and spread from SARS-CoV-2.

anti-ACE-2 antibody antibody attenuated SARS-CoV-2 entry into target cells
SARS-CoV-2 infects humans through the spike glycoprotein and ACE-2 receptor.
Credit: https://www.rndsystems.com/resources/articles/ace-2-sars-receptor-identified

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