The parasites imho are just a symptom of not eating and living properly.
Ask any hunter or any butcher or any cattle breeder (with his animals running in the wild) and he will tell you that all animals are infected by parasites to a degree.
Respecting hygiene principles and a smart handling of our water, of our feces and our waste, has allowed humans to live a better health with less infections.
In Africa or others countries where the hygiene is poor, many of these primitive people die because of parasites infection. They moves, they hunt, they awake and sleep with the sun, they eat primitive foods, but the mortality is high.
These are facts, not opinions.
Weston Price has done a study on the people who have survived or avoided these infections and who lived locally, when the life was still local compared to nowadays.
Parasites are traveling a lot in our modern world, through water, through waste, through, foods, through people, through sex, through pets, through travels, through blood donations.
You can't compare the old local world and our internationalized world... Our "local immunity", our "local evolution", our "local human body", call it what you want, may not have the power to defend itself against foreign parasites.