People are constantly surrounded by viruses and bacteria. E.coli is found in most bathrooms, things like salmonella live in kitchens, we garden in soil that might even harbor deadly bacteria, protozoa, and so on. If you have pets there’s even more germs they carry around and put on your clothes, bed, etc.
For the average, healthy, non-immunocompromised person, why are our immune systems able to protect from encountering these things daily, and what goes wrong when we do get sick? Why is it so easy to catch the flu from someone, but you’ll rarely get an e.coli infection from your toothbrush?
In: Biology
When we get those classic “sick” feelings— mostly called cold and flu symptoms— things like fever, fatigue, body aches, and other forms of inflammation, it is actually our adaptive immune system causing it, not pathogens. For our immune system to activate in this way, pathogens have to get past what is called our “innate” immune system. This just refers to the portion of our immune system that is always active or simple present. Skin barriers, the natural antimicrobial qualities of some parts of our bodies, specialized cells that are always ready to preform unspecific attack on pathogens, and our natural microbiomes are some examples of innate immunity. Generally, to evade these defenses something like an unusually large amount of bacteria or virus enters the body, a particularly sneaky virus, an open wound (compromised innate immunity), or something else that makes a persons innate immunity unable to stop the disease from spreading. This is generally the point at which someone is considered “sick”. Like I mentioned before, most of what we consider symptoms of infection is just a reaction of our immune system to detecting disease.
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