[nudephil (OP)]

Listener Gabriel sent us the following:

If you have COVID-19 but no symptoms, can it still damage your body?

Also I believe it has been argued that having too clean a home environment can in some ways be harmful to us. If this is true, could it impact on how we deal with the present pandemic?

Any answers?

[alancalverd]

It is difficult to imagine any kind of harm that could not be considered a symptom, though we do tend to discriminate between immediate symptoms of infection and late sequelae. AFAIK historic asymptomatic carriers (everyone quotes Typhoid Mary as the prime example) tend to live healthy lives until they die of something else.

There is anecdotal suggestion that lack of childhood exposure to "everyday dirt" (starting with vaginal delivery and breast feeding) is associated with later susceptibility to bacterial infection, but I don't know of any definitive studies. 

[set fair]

It is certainly possible for the virus to cause damage without apparant stmptoms. We have ACE2 receptors throughout the body. So a person might have some damage to their heart without noticing it and the damage may never be attributed to the virus. 

There are the happy hypoxics, people suffering low oxygen levels without knowing anything was wrong - we can only guess at how many of these never saw a doctor nor what dammage occurred.

[evan_au]

If you have COVID-19

This means that there are virus particles invading your cells, taking over, exploding outwards (destroying the cell), and repeating with other cells. Some of these virus particles find their way into your nose and throat, which is what the virus test picks up with a throat swab.

If the rate of cell destruction is low, your body can replace the lost cells, and it won't make you feel too bad (asymptomatic spreader).

The most severe cases appear to occur when the immune system reacts aggressively to the new invader, destroying tissues. Wholesale destruction of blood vessel linings, lung, kidney or heart tissue has severe consequences (especially with heart tissue, which regrows quite slowly). This has definite symptoms - blood clots in capillaries, shortness of breath, low blood oxygen, heart failure, kidney failure and death.

too clean a home environment

The "Hygiene Hypothesis" suggests that our ancestors met with many pathogens and parasites, and their immune system was focused on fighting off these pathogens.

However, in our modern antiseptic/antibiotic world, the immune system has nothing to do, and panics when it sees new, potentially dangerous invaders like pollen, cat fur, insulin and peanuts. This hypothesis suggests that an overactive immune system triggers many allergic responses like hay fever, asthma, anaphylaxis, Type 1 diabetes, etc.

It is known that diabetes is a risk factor for COVID-19 severity. It is quite possible that the people who are suffering severe COVID-19 do have this overactive immune response.

Perhaps people in the poorer areas of Rio or in the Amazon jungle may not have such a severe immune reaction to the virus? But we may never know, as there is little or no testing being done there, there is inadequate record-keeping, and little or no hospital access so they can get treatment comparable to those in more affluent areas.

See: https://en.wikipedia.org/wiki/Hygiene_hypothesis

[evan_au]

happy hypoxics, people suffering low oxygen levels without knowing anything was wrong

I know two people who had an undiagnosed hole in the heart for many years. Both of them were shorter than average; you might expect whole-body effects from oxygen deprivation (but you can't tell from this small sample).

A recent case was diagnosed only when he was over 50 years old. He went into hospital for an unrelated surgery. Standard procedure in the recovery ward is to wait until your oxygen saturation approaches 100%. His remained very low (under 70%) and did not improve. He had to repeatedly tell doctors that he did not smoke... They eventually thought of checking for a hole in the heart...

You would think that hospital staff would check oxygen saturation before you went in for surgery - that is important for an anesthetist to know!
See: https://en.wikipedia.org/wiki/Atrial_septal_defect