SHEDDING LIGHT ON THE COVID-19 VIRUS
March 19, 2020 § 2 Comments
If enough of the light was at ultraviolet wavelengths, the virus would die. This light, however, is an attempt to explain some of the science behind the virus and its effects. I fully expect you folks to obtain fact or inference checks from physician scientists and am prepared for the comment onslaught.
A general caution is that very few sites, including this one, ought to be relied upon without verification. The reputable sites include the National Institutes of Health (NIH) and in particular the National Institute of Allergy and Infectious Diseases (NIAID), the Center for Disease Control (CDC), and the World Health Organization (WHO). Other sources are sites at top medical schools such as at Johns Hopkins, Stanford and Harvard.
First the nomenclature. COVID-19 is the disease resulting from the virus. The virus is from the general family of coronaviruses, with this variant being named SARS-CoV-2. SARS stands for Severe Acute Respiratory Syndrome. The name being a bit of a mouthful, the WHO often refers to it as the “COVID-19 virus”. The virus is related to those responsible for the recent outbreaks of SARS in 2002-2004 and Middle East Respiratory Syndrome (MERS) in 2012.
Structure and function
In common with other coronaviruses, they are spherical, with protein spikes sticking out about 12 nanometers (nm). Resemblance to a crown informs the corona name. They also have a striking resemblance to the fearsome medieval weapon, the mace. In size they are reported to be in the range 50-150 nm, which places them roughly in the ultrafine classification of airborne aerosols. However, deposition fractions in various parts of the respiratory tract cannot be presumed to be similar to those of particulate matter, even those coated with organic molecules.
SARS-CoV-2 transmission electron microscopy image, courtesy NIAID-RML
The image is of a virus isolated from a US patient. The spiky proteins attach to receptors in human cells. The mechanism is not unlike a lock and key. The key of the virus protein needs a receptor lock to attach in order to then enter the cell. Another analogy is docking of a spaceship to a space station. Once this docking happens, the virus can enter the human cell. Then it can replicate in the human cells and the disease is well on its way. Recent research has shown that the receptor for SARS-CoV-2 is the same as that for the SARS virus. That is the good news, because we know a lot about the original SARS. The not so good news is that the binding affinity for this virus is ten to twenty times greater than for the original SARS (Wrapp et al. 2020). This could explain why the human to human spread appears to be greater than was noted in the SARS outbreak. Furthermore, despite the similarities in the structure and sequence of the protein spikes of the two viruses, three antibodies developed for SARS were not effective in binding to the SARS-CoV-2 protein spike.
A feature of the SARS-CoV-2 virus is that it is enveloped by a lipid (fat) layer (the “crown” protein extends beyond the lipid layer). In this aspect the structure is like that of influenza viruses and the other coronaviruses (and unlike the diarrhea inducing rotavirus). This is fortunate because soap and water will kill it. Soap has a hydrophilic head and a lipophilic tail. The tail penetrates the lipid layer and pries it apart, thus leading to the destruction of the viral genes, with all the fragments being washed away by the water. This mechanism of action underlies the most important public health guideline for minimizing spread, washing of hands in soap and water for at least 20 seconds, taking care to wash between the fingers. Hand sanitizers are believed effective if they contain at least 60% alcohol. They too remove the lipid layer and cause the disintegration of the virus.
Except for the hand cleaning discussion, I did not get into disease avoidance. For the rest you need to go to one of the reputable sites. But I will note that my limited examination of the literature shows a flurry of scientific activity on several fronts. These include studies of the immune response, development of a test to verify the presence of antibodies (UK), testing of intensity reduction drugs (example Tamiflu for influenza), and research on the ultimate prize: vaccines. Keep in mind that folks are rushing to publish, in order to get the information for others to use, and so findings may be subject to revision. The study linked above is based on a single patient, but still instructive. With all the stuff out there, caveat emptor!
Reference: Wrapp et al., (2020) Science 367, 1260–1263
Vikram Rao, March 19, 2020