tough parasites = no parasites. That's why they never seem to go away because they are not actually there.
People's bad diets, calorie-restriction, and other unhealthy lifestyle choices has led to people getting an array of symptoms and they've either misdiagnosed themselves as their problems being caused by phantom parasites, or where misdiagnosed by some quack alternative practitioner who's all to willing to sell their desperate and gullible patients some expensive bottle of supplements or cleanse.
And then they were probably recommended an anti-carb/gluten diet, high in fat, oils, and animal protein, that is just making them even sicker.