Cold symptoms vary wildly from one cold to the next, both in array of symptoms and severity. I’m curious about this variation.
Basic reading about the common cold suggests that certain cold viruses (among the hundreds) lead to more severe symptoms than others. This matches my anecdotal experience: when the whole family gets a cold, it (sometimes?) seems to hit similarly hard or not for all of us. I would guess that viral load plays a big role (yes?), but variations in immune response might, too (or maybe this isn’t such a big randomizer for colds?)
Question 1: Is there an established correlation in the severity of symptoms when two people get the same virus?
Regarding types of symptoms: Colds seem to manifest in different ways. A few example cold progressions might be (i) raging sore throat, then lots of mucus, headache; no noticeable cough, or (ii) no sore throat at all but severe loss of voice, minimal mucus throughout, or (iii) “chesty”, even painful cough that lingers, with a sore throat to start, some mucus, or (iv) a bit snotty for a few days, but not much else. Etc.
I’ve always reckoned that the most severe symptoms occurred at the sites where the primary infection happened. For example, if the virus infects the larynx or nearby tissues directly, you will lose your voice. Or, if the virus infects the bronchial tubes directly, you will get a much worse, chesty cough. Or, if the virus infects the sinuses directly, you’ll generate more mucus and, depending on which sinuses are most affected, headache or “pressure”.
Question 2: Is this picture – a correlation between site(s) of infection and dominant symptom(s) – correct in any way? Does the infection quickly fill the entire upper respiratory system anyway no matter the path of infection, or is it more localized (as the symptoms would naively suggest)?
If localization is a part of the story… Again anecdotally, I can recall many colds where the melange of symptoms seemed similar across victims, but the sample size is too small to believe anything.
Question 3: Do certain cold viruses prefer certain tissue types (e.g., bronchial tubes vs. sinus cavities vs. throat)? Is there an established correlation between viral strain and dominant symptom(s)?
And finally, you never hear of other mucus membranes around the body getting infected with cold viruses despite the obvious activities that could transmit infected fluids. So, I assume it can’t happen.
Question 4: What distinguishes the respiratory mucus membranes from other mucus membranes vis-a-vis infection with cold viruses? Why do cold viruses only infect the respiratory tract?