Thursday, October 27, 2022

Covid is a Stealthy Enemy; Our Body its Battlefield -- Shore up Your Defences, and Fight to Keep it at Bay!

Dr. Uppity (@MeddygLou), an NHS GP in Wales, wrote an excellent thread, beautifully written, explaining how Covid works with some battlefield imagery to help. I have nothing to add:

Since Covid hit the UK I’ve been reading compulsively, like how you can’t help looking as you drive past a car crash. There’s a lot still to research, but I’ve made a rough working model in my mind of how Covid attacks the body, and what the main issues can be. Covid virus travels through the air, a bit like invisible smoke. Covid is airborne. It’s also in droplets of spit & mucus in air or on surfaces, but that’s not the main way it transmits. Wash your hands & stick up a screen if you like, but improving indoor air quality & masks will do far more to protect you from infection. 

Once you breathe in air with the virus in it, the virus attaches itself to the cells that line your nose, throat, voice box, windpipe & lungs. It gets into the cells using ACE2 receptors as a “door.” ACE2 receptors are also found in the lining of the gut, the lining of your blood vessels, and many other organs, giving Covid easy access to these areas. In the lungs there’s just a thin layer of cells between the air & the bloodstream. The virus gets into a lung cell using the ACE2 “door,” then hijacks the cell’s factory area to make rough copies of itself. Lots and lots of copies! It may also turn up secretion production, so on one side the cell starts releasing mucus full of new viruses into the lungs. These can either infect more lung cells or get breathed out into the air to maybe infect someone else. On the other side is the bloodstream, where more new viruses are released. The lining of the blood vessels, the vascular endothelium, also has ACE2 “doors.” Now the virus can infect the lining of the blood vessels in the lungs, AND travel round the entire body, infecting any bit of blood vessel wall as it goes. 

By now the body knows it’s under attack. It can “see” the naked viruses floating in the blood stream. Immune cells start noticing the virus. B cells make an antibody that “fits” to the “shape” of parts of the virus. Once the antibody locks onto the virus it acts as a “flag” attracting other immune cells to destroy & remove the virus. Now there’s a war; the immune system ramps up its activity to try to mop up all the free virus before it can infect cells and make even more virus. Chemicals are released to call more troops to battle. Cells that are already infected have to be identified and killed. It’s probably a bit approximate, but I think of this collateral damage, the chemicals, the dead cells, the immune cells, and the “flagged” (optimised) viruses, as “inflammation.” Inflamed organs don’t work so well. There’s too much fluid drawn in to carry the immune cells, lung cells are getting killed off and have to keep replacing themselves. Oxygen crossing over into the bloodstream has to go through all this inflammatory fluid & debris. 

On the blood vessel side, things are even worse. When the blood vessel lining gets damaged it attracts platelets. Normally if a blood vessel is cut you want a clot to plug the hole so you don’t bleed out. But there’s no hole here, only inflammation, and now little bits of clot. Microclots can break off and float around in the bloodstream, maybe breaking up, maybe getting caught in the tiny capillaries causing tiny areas of lost blood supply. This might be one of the ways LongCovid makes some of its effects. If you’ve been recently vaccinated (or infected) your B cells already have some idea what Covid “looks” like, so they’ll be quick off the mark with antibodies that at least roughly “fit” onto the virus, making it easy to mop up before too many cells get infected. If you haven’t been vaccinated, it takes a while for the immune system to get going, giving the virus time to travel further, infect more cells, & set up more “factories” making even more new virus. The immune system’s learning curve can be enough for it to lose the war. 

There are ACE2 “doors” into lots of different types of cells in the human body. Kidney, liver, pancreas, gut, brain, muscles, testes/ovaries, bone marrow & many more. Some cells are used to replenishing themselves quickly and can be readily sacrificed to clear the virus. Some cells are not easy to replace. The immune system seems to know this and is less keen to attack virus hiding in these places. Brain cells and nerves are very slow to be replaced, as are heart cells, egg cells, stem cells & muscle cells. So one theory of LongCovid is that the virus could be sticking around hiding in one of these places, where the immune system is reluctant to cause too much damage. Other viruses do it: chickenpox virus lives in nerve cells for a lifetime, HIV in immune cells. 

Which brings me to my biggest fear for the future: reactivation syndromes. When a virus inhabits a cell long term it still churns out new viruses, so the immune system has to be constantly active nearby mopping them up before they can go anywhere. Constant activity could be draining for your body, another LongCovid possibility. But if you get run down the virus might start winning. It might reactivate, doing something new and different to get around your defences. Shingles for chickenpox, AIDS for HIV. For Covid ??? Balancing a constant threat without causing too much collateral damage may also cause other problems for the immune system. It may slip up in its regulation and let out antibodies that flag its own cells to be attacked. Autoimmune diseases. Some LongCovid could be these. 

If you’re not scared by now, you’ve not been paying attention, but there’s more. When you breathe in Covid in the air it doesn’t just go to your lungs; it goes through your nostrils too. From the nasal mucosa it can get into the olfactory nerve, which does smell & taste. The olfactory nerve goes through holes in you skull straight into your brain. Brain cells are meant to last a lifetime. You don’t want an infection, or any inflammation, in here. Another potential source for LongCovid, then, is long term infection of brain cells.

 My advice: avoid this nasty virus. We know enough to know it’s very bad news. Wear a good mask (FFP2 or 3 or N95), ventilate, filter indoor air, get vaccinated whenever it’s offered. If I’ve over-simplified at the expense of accuracy, or made any mistakes, let me know. 

More on the brain: MRI changes show more generalised shrinking of the whole brain - something which happens normally with age - but more shrinking than you’d normally expect in those who’ve had Covid. It also seems to single out the hippocampus - the bit that makes memories & retrieves them, & the orbitofrontal cortex - a bit with a complex function in giving things value, eg. deciding what smells nice/nasty, recognising faces, attaching emotional responses to different situations or behaviours, and learning to change behaviours that are unhelpful or cause harm. It’s an area that doesn’t work well in people with OCD or ADHD. More on the heart: the risk of heart attacks & strokes seems to increase for everyone for at least a year after a Covid infection. Whatever your background risk was, it multiplies by about 1.5, which sounds small, but is huge on a population level. It’s only slightly less than the impact of taking up smoking 10 a day. I can’t believe I forgot to mention the immune system. The virus can infect cells in the immune system. We don’t know how often it does this, but we know it can. It can infect stem cells, too - the new cells with potential to become blood cells or white cells. Either through directly infecting the immune system, or by creating an ongoing war in the rest of the body, we know that the supply of some immune cells becomes depleted. 

Covid reduces your ability to fight off all future infections. We don’t know how often or for how long. This effect could be responsible for the increased flow of other diseases through the population. It could also be part of the reason for repeated infections and our failure to achieve “herd immunity,” but at the moment, probably not the main reason. The main reason herd immunity won’t happen is that the virus mutates faster than we can build immunity to it. Vaccines could help, but we are running transmission so high that new variants can develop really quickly. Faster than we can vaccinate against the old ones. Thanks to Covid we will have more of every kind of infection this winter, more heart attacks, more strokes and more of many other kinds of disease. Our health service hasn’t had the funding to cope with more of anything. The NHS is already struggling with years of cuts. I repeat my advice: do whatever you can to avoid this nasty virus. Masks work, especially FFP2, FFP3 & N95. Diluting the virus with clean air works, ventilate, open windows. HEPA filters work. They clean all kinds of virus, dust and pollen from the air. Stay safe and well!  

Images from Fight the Pandemic.  

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