The symptoms we get when sick are rarely characteristic of any one sort of infection. Our bodily systems respond in a similar & rather general fashion to all sorts of things. And we do adapt & coevolve with diseases. That's why it's dangerous to make contact with remote tribes. People of european descent all have ancestors who lived in close quarters with their livestock for many centuries. We now carry around all sorts of things that would have been dangerous to people at some time in the past.
How do you know this?
Guns Germs & Steal is a decent read. Reading about & studying health stuff. Spending a lot of time browsing health groups & forums around dietary advice & other things. Paying attention to gardening & permaculture stuff. The same patterns are everywhere. The names for "diseases" people get are mostly just bullshit that someone made up. There are a handful of things that happen when people get sick. There are a handful of things that happen when plants get sick. The root causes have more to do with some sort of damage or deficiency that makes the infection possible. For example, it seems pretty clear that Polio was the result of lead arsenic pesticide poisoning which permeated the gut lining & damaged lots of body tissue near the intestines, the most important tissue being the spinal cord. Damage to the spinal cord in the gut region makes them unable to walk. When something passes through gut tissue (creates leaky gut conditions) it can shuttle in all sorts of pathogens that are almost always present & would otherwise be harmless. So the problem isn't the pathogen it's the substance that granted the pathogen access to parts of you where they can do harm. But blaming the pathogen allows pesticide companies to escape liability & pharama corps to sell a new treatment.
I agree with most of that. How do you know that "pathogens" are "almost always present" and under certain conditions become hazardous?
Well, getting poop on everything would be a problem because poop is loaded with potentially harmful stuff. Hygiene is important because I think there are certain levels of viral or bacterial load that can become more dangerous. But if you sterilize a container & put sterilized or freshly cooked materials in it it keeps very well. If you put biodegradable things in a container that hasn't been sterilized then things will grow pretty quickly. And we did bacterial tests of different surfaces in highschool. All of which seems to suggest that there are low levels of potentially harmful things everywhere. Which makes sense, there is also visible dust & pollen & bugs everywhere (you generally have to wipe off a seat that's outside every day, sometimes more than once in the same day), why would it be any different on a microscopic level? They just don't matter most of the time because our gut (and the rest of our system) is good at either putting them to work in the digestion process and/or keep them out of the body.