Day 16: Saturday. Benign viruses.
This morning I slept in an hour or more, and went for my walk late, so I met a few more people. There were two old ladies who had solved the problem of staying 2 metres apart on a 1.5 metre sidewalk by not using the sidewalk. Since there are effectively no cars about, it becomes safe to walk down the roadway, and they were doing so, side by side but well separated. "Good distancing, I see!" But my lungs must be getting old: they begin to ache even when walking at full speed. Possibly jogging would be a more efficient gait at that speed, but I want to preserve my joints.
You've heard of what the medics call "benign tumours", right? They're not actually beneficial, but neither are they malignant: they don't grow much and don't do significant harm. You've also heard that we have huge populations of bacteria in our guts, on our skins, and probably in other parts of our bodies, some of which are beneficial, and many more of which are benign in the medical sense. So it seems more than likely to me that there are benign viruses, probably in ridiculous numbers. Even SARS-CoV-2 is presumably benign to the bats that carry it in the wild, and quite possibly to some fraction of humans. It is suspected that some parts of the human genome are in fact viruses that have, so to speak, immigrated and found jobs within human cells.
Now, what would make a virus benign to us? First, I suppose, is its rate of reproduction within the host. A virus that keeps its population roughly the same, or multiplies slowly enough that our bodies can simply excrete the additional particles, may do little or no harm; one that multiplies rapidly will make heavy demands on the metabolism of a cell it enters, preventing that cell from doing its normal job, and thus causing at least some symptoms, though perhaps only weakness and fatigue at first. I'm no immunologist, but I suspect that what happens next depends on our immune system. If it ignores the virus, the virus will overwhelm our bodies, causing organ failure and death. If it notices the virus enough to raise a fever, this may slow the virus' replication, or perhaps not, and also won't do us much good. [Suddenly I understand why our not-so-remote ancestors believed that a fever should be allowed to spike. If the pathogen is sensitive to temperature, a high fever can kill it, which is what should happen.] If the immune system mounts a stronger response, well, that is how CoViD-19 kills us: the lungs get inflamed as massive amounts of cytokines are released, and the treatment that seems to work is an immunosuppressant. So another criterion for a virus being benign is that it must not over-stimulate our immune system.
I could ramble on about the idea of modern hygiene leading to poorly developed immune systems and higher prevalence of allergies, but you can read about that sort of thing on the Web, and there may even be books about it.
So why am I wondering about benign viruses? Because I'd expect them to mutate into something nasty now and then. They don't exactly know that they're better off leaving the host alive; they don't know anything. Our immune systems would presumably recognise them as self rather than foreign. But that doesn't seem to happen. Evidently I'm not a virologist. Some of our benign bacteria are quite closely related to strains that cause disease, such as Staphylococcus and Streptococcus. So what makes the difference?
You've heard of what the medics call "benign tumours", right? They're not actually beneficial, but neither are they malignant: they don't grow much and don't do significant harm. You've also heard that we have huge populations of bacteria in our guts, on our skins, and probably in other parts of our bodies, some of which are beneficial, and many more of which are benign in the medical sense. So it seems more than likely to me that there are benign viruses, probably in ridiculous numbers. Even SARS-CoV-2 is presumably benign to the bats that carry it in the wild, and quite possibly to some fraction of humans. It is suspected that some parts of the human genome are in fact viruses that have, so to speak, immigrated and found jobs within human cells.
Now, what would make a virus benign to us? First, I suppose, is its rate of reproduction within the host. A virus that keeps its population roughly the same, or multiplies slowly enough that our bodies can simply excrete the additional particles, may do little or no harm; one that multiplies rapidly will make heavy demands on the metabolism of a cell it enters, preventing that cell from doing its normal job, and thus causing at least some symptoms, though perhaps only weakness and fatigue at first. I'm no immunologist, but I suspect that what happens next depends on our immune system. If it ignores the virus, the virus will overwhelm our bodies, causing organ failure and death. If it notices the virus enough to raise a fever, this may slow the virus' replication, or perhaps not, and also won't do us much good. [Suddenly I understand why our not-so-remote ancestors believed that a fever should be allowed to spike. If the pathogen is sensitive to temperature, a high fever can kill it, which is what should happen.] If the immune system mounts a stronger response, well, that is how CoViD-19 kills us: the lungs get inflamed as massive amounts of cytokines are released, and the treatment that seems to work is an immunosuppressant. So another criterion for a virus being benign is that it must not over-stimulate our immune system.
I could ramble on about the idea of modern hygiene leading to poorly developed immune systems and higher prevalence of allergies, but you can read about that sort of thing on the Web, and there may even be books about it.
I've just looked at the NYT's graph of deaths. That is likely to be more truthful than graphs of cases (it is not all that difficult to test for death), and tells a very mixed story. Iran is, after a bad start, following China's trajectory, and I note that Iran has a heavy-handed government by our standards; a total death toll of 3k seems on the cards. South Korea is doing very well indeed, and may get away with just a few hundred deaths. Italy's graph is curving over a bit as of this week, from about 12-14 days after Lombardy was locked down, but 100k deaths look likely. Spain is climbing relentlessly, as are France and the UK ... and the USA even faster, after a slow start. I think Bill de Blasio has a lot to answer for (nor is Andrew Cuomo innocent). He delayed locking his city down until several days after Gavin Newsom had locked a whole state down. I notice that the President is praising him. Don't even ask me about India.
So why am I wondering about benign viruses? Because I'd expect them to mutate into something nasty now and then. They don't exactly know that they're better off leaving the host alive; they don't know anything. Our immune systems would presumably recognise them as self rather than foreign. But that doesn't seem to happen. Evidently I'm not a virologist. Some of our benign bacteria are quite closely related to strains that cause disease, such as Staphylococcus and Streptococcus. So what makes the difference?
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