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Side note #1 – Viruses come with DNA or RNA genomes. A positive PCR result does not prove active replication of a virus. It does not prove infectious virus is present. This is why we prefer to talk about a virus being detected in patients using PCR. Some refer to a PCR positive result as a “viral isolate” – don’t. This should be reserved to describe eh successful growth of a virus using cell/tissue/organ culture.
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Side note #2 – if we’re looking to declare such a person “asymptomatic” – we had better be completely sure they have absolutely no symptoms of an infection. Disease, a deviation from normal body function, may be as mild as a headache or just feeling crook – and still, pedantically, be a disease ascribed to the virus detected by PCR. Let’s assume that level of care has been taken (often it hasn’t)
Side note #2 – we are walking platforms for viruses, bacteria and fungi. Take a look at this paper from Eric Delwart; in 2 kids-92% of 72 samples collected weekly over more than 250-days were virus-positive (no or mild signs of disease developed during this time)! It is very likely, as we discover more diverse agents, better characterize them and develop (and use) improved capabilities, that we will learn we’re hardly ever without a passenger or 3. And yet we are not always sick – why is that?
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Immunity can keep us well, even if infected.
The immune system to the rescue! We have a very capable, active and multifunctional immune system. It is constantly being challenged by…things – not just viruses, bacteria and fungi but chemicals, various proteins, carbohydrates, allergens, dirt and dust (composed of bits of all that other stuff) and it does a great job of sorting through it all, responding to what it needs to, to prevent disease, and usually squashing the response to the rest in such a way that we don’t under-perform 24/7 because of allergy and illness. It is due to this complex system that we shouldn’t be surprised that as technology lets us find lower levels of infectious agents, it is completely reasonable to be “infected” but not diseased. At least in some proportion of our encounters with viruses, this should be no surprise.