SARS-CoV-2 : the virus

I’ll say one thing for the coronavirus outbreak, it has prompted a lot of curiosity. Whether you believe we are going back to the days of the plague pit, or it’s nothing but a severe cold, I have been asked a lot of questions about viruses in general and the coronavirus in particular. I’m not an epidemiologist, but I’m pretty sure the plague pits will remain safe in history. That’s no reason for complacency however, because this virus has the potential to cause widespread illness and far-reaching disruption. How widespread and far-reaching we will have to wait and see. And if anyone reading this thinks the coronavirus is an escaped bioweapon or made by big-pharma so they can sell more drugs, then I will save you time and tell you not to bother reading any further.

The term coronavirus relates to a number of viruses mostly circulating in animals. Occasionally they jump from animals to humans, as with SARs which appeared in 2002. That virus was the SARS-Cov-1 and now the latest has been designated SARS-CoV-2. Based on genomic analysis SARS-CoV-2 is closest to a strain of coronavirus known as BatCov RaTG13, carried by bats.

In this post, I will not get into the possible consequences of viral spread – I honestly don’t feel qualified to make such judgements. Instead I thought I’d quench the curiosity of those who have asked me about viruses, how they infect and what we can do about them. This takes me back to my old profession – pharmacology.

It is one of those quirks of history that we had vaccines against viruses before we knew viruses existed. Although their existence had been suspected for some time, it wasn’t until the electron microscope was invented in 1931 that viruses were first seen. Which means that medicine was ignorant of the viral cause of the Spanish flu pandemic in 1918 which infected half a billion people world-wide.

The reason viruses evaded detection was because they are tiny, ranging between about 20 to 400 billions of a meter in diameter. To put their size into context, if the smallest of the viruses were enlarged to the size of a football* then that is on the same scale as enlarging a football to a sphere with a diameter from London to Rome. SARS-COV-2 is a relatively large virus, coming in with a diameter of around 200 billionths of a meter. Although it’s carried in water droplets, there’s no evidence for airborne spread and its size may be a contributing factor for that.

Viruses inhabit the twilight world between living and non-living. They are constructed from genetic material, protein and some sugar and lipid. SARS-COV-2 does not contain DNA but RNA (ribonucleic acid), which like DNA comprises a string of bases in the form of a helix. Viruses cannot live alone. They invade cells and take them over like some ultra microscopic version of invasion of the body snatchers; turning the cells into viral factories, which pour out many more viruses to invade other cells.

Viruses invade cells through protein spikes on their surface. Proteins can be likened to a biochemical set of spanners and wrenches, each shaped to fit some other biological molecule – typically another protein. When the “spanner” protein fits onto another, it twists into a new shape which elicits some biological response. With viruses, the protein spikes latch onto cells which twist an opening in the membrane allow them to enter. These spikes are essential to viral infection and they are also their Achilles’ heel when it comes to fighting them. The structure of the SARS-COV-2 spike is now well characterised (see image) and is a target for new anti-viral drugs.

Antibiotics are useless against viruses and can only be used to treat bacterial infection. (There is a class of virus called a bacteriophage that attacks bacteria, but that’s another story). Developing anti-viral drugs is tricky because it’s a tightrope between killing the virus and the cell it’s invading. If the anti-viral does the latter, then the reason for side-effects becomes obvious. The spike-protein offers something specific to a virus, not found in human cells, for a drug to attack. The best known antiviral drug, Tamiflu (Oseltamivir), works in this way. It attacks a protein called neuraminidase on the viral surface, preventing it from release and infecting other cells. Another anti-viral called ritonavir is used to treat HIV by targeting a protein that inhibits the reproductive cycle of the virus. I am proud to say I have done a small amount of research on ritonavir – tiny in the big picture of drug development admittedly. The effectiveness of ritonavir against the current virus is being assessed.

What about a vaccine? The specifics are outside my field, but, similar to anti-virals, vaccines target specific proteins on the surface of the virus. Our immune system constantly looks for things it considers foreign to the body and it does that through our old friend proteins. These proteins are called antibodies and they latch onto non-self proteins, essentially painting a target on them to prompt attack from other components of the immune system such as white cells. A vaccine elicits appropriate antibodies to the virus, which then patrol the body and knock them out before they do too much damage. As I say this is outside my field but I get the feeling there’s a lot of misinformation going around about the development of a vaccine. Knowing the structure of the viral proteins helps but it’s likely to be a year or more before a vaccine becomes available.

A final word on hand-washing. Here in the UK, and I believe some other countries, stocks of hand sanitizer are sold out. The fact is however, soap and water is probably more effective. The virus has a lipid coat known as a capsule and it is disrupted by detergent. It’s like removing grease from a frying pan with washing up liquid (trying doing that with hand sanitizer). The thing about washing your hands for 20-seconds, is not just about removing the virus, but it gives time for the soap to act on the lipid capsule.

Advice varies as to how to time 20-seconds when hand-washing. Some say it’s the time it takes to sing two versus of happy birthday. One of our Members of Parliament (Jacob Rees-Mogg) suggested singing Rule Britannia. Such are the times in which we live.

* – a soccer ball, not an American football

(Edited and corrected, 17 March 2020)

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