Cat and Mouse

A few weeks ago I had a conversation with a friend. She is intelligent, well read, and generally well informed. We were discussing our lives and she noted that I am the most Covid conscious person she knows. I made a remark about the brain damage Covid causes, and she was shocked. She hadn’t heard about it. I always assumed that this knowledge was at least vaguely understood by the general public, but I was wrong. Hence this essay.
The punchline up front: Covid-19 causes brain damage in 100% of cases. It’s usually incremental, but it has measurable effects.
You have probably heard about an effect of Covid called anosmia, loss of smell. The virus gets in through the nose and travels up to the olfactory bulb in the brain, causing damage. Right next to the olfactory region is the orbitofrontal cortex. Neurologists have done follow up MRI scans of people who had brain MRIs in 2019, some of whom had gotten Covid, and some not. There was visible brain shrinkage in the Covid group. Another focus of damage is the parahippocampal gyrus. (1)
There is a type of scan called PET-CT that can detect levels of sugar metabolism in parts of the brain. Basically, how active parts of the brain are. Neurologists have done PET-CT scans on people post Covid and noted hypometabolism (below normal activity) in the orbitofrontal cortex. (2) Covid degrades the brain’s ability to metabolize glucose in general, which could be a major factor in the mental exhaustion and well known “brain fog” associated with long Covid. There is an increased risk for Alzheimer’s and Parkinson’s disease post Covid. (3)
Other researchers have given standardized cognitive tests to groups of people who haven’t gotten Covid and then retested them after half of the subjects had gotten Covid. Everyone in the Covid group showed cognitive deficits in the retest. (4) Other researchers used MRI scans to study connectivity between areas of the brain in subjects post-Covid. They found that anosognosia (the inability to recognize a cognitive deficit in oneself) was associated with lower connectivity, worse measured cognitive outcomes and yet better subjective self-assessments. (5)
Another study looked at Covid and car accidents. It found that, regardless of vaccination status, getting Covid increased accident risk by a factor of 1.5. That brings us back to the orbitofrontal cortex (OFC). (6)
The OFC does a few things, but one of its main functions is risk assessment. It calculates the consequences of our actions. People with damage to the OFC experience less or no anxiety when making risky decisions. The OFC also has a role in emotional regulation. The increased accident rate makes sense. Post Covid, people are less capable of calculating risk, less anxious about taking risks, and less emotionally regulated.
I also mentioned the parahippocampal gyrus. That region is involved in the creation and retrieval of memories. Memory issues are a common complaint post Covid.
There are a variety of other health issues resulting from Covid, from erectile dysfunction to heart attacks, but these are all a matter of odds. A 28% increase in the incidence of ED. A doubling of the incidence of heart attacks and strokes. Between 1.6 and 3 times the usual rate of overall mortality in the year following, depending on severity. The thing that distinguishes Covid caused brain damage is that it happens in 100% of cases. I’m interested in the why of a 100% incidence of brain damage. A virus is just a bundle of genetic material in a microscopic bag. It has no agenda except making more of itself. It doesn’t calculate, it just mutates and gets tested against its environment.
It makes evolutionary sense for an infectious disease to damage the brain, especially the orbitofrontal cortex. An infectious disease that degrades a host’s ability to assess risk and regulate behavior is a disease that has more chances to infect and reinfect a host species.
I will note that Covid also suppresses a neurotransmitter involved in the transmission of pain signals to the brain. (7) That means that Covid sufferers don’t suffer as much as they might otherwise. There are also accounts of people with other sources of pain getting temporary relief during the acute phase of Covid. (8) Feeling less sick would lead to more activity and less caution, leading to more infections.
It’s anecdotal, but I have read a number of accounts of people who have had multiple cases of Covid and can no longer remember that they have had multiple cases, or how debilitating the experience was.
This is where we get to the cat and mouse of the title. There is a microorganism called Toxoplasma Gondii. It infects cats and rodents such as mice. However, it needs to be in the digestive system of a cat in order to reproduce. It has evolved to modify the neurology of mice in such a way that they become unafraid of the smell of cats. (9) Normally the smell of cats makes mice anxious and cautious and they tend to leave the area. T. gondii infected mice are actually excited by and attracted to the smell of cats. Bad outcomes result for the mice; necessary outcomes for T. gondii. This microbe is one of a class of organisms known as host manipulating parasites.
Host manipulating parasites change the behaviors, the metabolism, and even the body shapes of their hosts in an effort to promote their own survival. There’s a worm that parasitizes crickets, but needs to enter water to reproduce. It induces its cricket host to jump in the water and drown so that it can live. There’s a trematode that infects ants but needs to get to the digestive system of a cow to continue its life cycle. It makes the ant climb to the top of a blade of grass and stay there, where the ant might more readily be eaten by a grazing ruminant.
Could Covid have evolved into a host manipulating parasite? There certainly were (and are) social and political factors that induce people to forgo masks, testing, air quality interventions, and other behaviors that slow an epidemic.
Still, overlaying it all I witness a strange apathy in the face of an epidemic disease. A disease, I should add, that is still killing a thousand people a week and permanently disabling tens of thousands a week. Everybody knows of at least one person who is either dead or disabled from it. We’ve all heard of long covid and seen the results.
At least three quarters of Americans have had Covid, so we have a large cohort of people with orbitofrontal cortexes operating at partial capacity. That same cohort has impaired memory and emotional regulation. On top of that, anosognosia, the inability to recognize that something has been lost. Just a general recognition that “people sure are driving crazily these days” and “kids are having trouble behaving in school.” It certainly seems as if Covid is making our species a better host for its proliferation.
Some people reading this might feel insulted at being described as having brain damage. No insult intended. Think of it as having blown out the ligaments in your knee and being told that you’ll never run quite as fast as you used to.
Our tendency is towards normalcy bias. In a disaster situation, people tend to go through three stages: Denial, Deliberation, and Decision. In a building fire or a shooting incident, people’s first tendency is to behave as if it isn’t happening. It can’t be. Those things only happen somewhere else, to someone else. Then, when realization dawns, people delay action. They look at what other people are doing, while those people look at them. People discuss the situation. Eventually people decide on an action. Much of the time it is ineffective or inappropriate to the situation. Many people just shut down, become inert, give up. A lot of people die in the first two stages. The people who survive disasters tend to fast track these stages; instantly accept the reality, decide on a plan, and execute it immediately.
It seems to me that most of this country is still in denial, or has gone directly to the shut down stage.
What should people who have had Covid do? Become consciously risk averse. Make it a habit to deliberately weigh options and think through future scenarios. Less instinct, more calculation. Deliberately drive more cautiously than you think you should. Use cruise control to stay at the speed limit and reduce cognitive load. The damage is incremental, but an incremental increase in risk added up over thousands of instances becomes significant. Wear a real N95 or N99 mask in enclosed public spaces. Wear it properly, adjusted to your face. Yes, be that weirdo. Your brain is on the line. The last thing you need is another hit to your cognitive capacity.
If you are community minded, push for indoor air quality improvements (filtration and ventilation) in schools, hospitals, public buildings, and businesses. This has been shown to dramatically reduce infection rates for all airborne diseases.
Covid-19 has evolved to make us careless. Don’t let yourself be manipulated by a mindless virus.
A good resource for the curious: https://youhavetoliveyour.life/
Footnotes:
1) https://pmc.ncbi.nlm.nih.gov/articles/PMC10063523/
https://www.nature.com/articles/d41586-022-00503-x
2) https://pmc.ncbi.nlm.nih.gov/articles/PMC9281418/
https://pmc.ncbi.nlm.nih.gov/articles/PMC7196385/
3) https://www.thelancet.com/journals/laneur/article/PIIS1474-4422(24)00178-9/fulltext
4) https://www.sciencedirect.com/science/article/pii/S266703642400013X
5) https://pubmed.ncbi.nlm.nih.gov/35350554/
6) https://www.neurology.org/doi/10.1212/01.wnl.0001051276.37012.c2
7) https://link.springer.com/article/10.1007/s10441-021-09425-z
8) https://pubmed.ncbi.nlm.nih.gov/34654780/
9) https://www.scientificamerican.com/article/common-parasite-could-manipulate-our-behavior/
https://pmc.ncbi.nlm.nih.gov/articles/PMC4512725/



