Parasites are my main go-to when I meet someone complaining about the modern world. In the history of multicellular organisms on earth, only (some) humans—and only in the last ~100 years—have had the luxury of not being completely infested with parasites.

Even now we have more parasites than we probably know or care to admit.

This was / is likely a factor in the "kernel of truth" with the whole "deworming tablets cure covid-19" thing, the chances of survival of people in certain areas infected with the virus increased if they were administered deworming medication because they also had a parasitic infection.