We have existed as some sort of human being for millions of years. It is a very safe bet that during that time well over 99% of population has existed with gut parasites. A bad thing ....right? No so fast. Check this out.
BB
https://www.sciencenews.org/article/having-worms-can-be-good-gut?utm_source=Society+for+Science+Newsletters&utm_campaign=a66a9099d5-editors_picks_week_of_4_11_16_4_16_2016&utm_medium=email&utm_term=0_a4c415a67f-a66a9099d5-90420405
http://www.medicalnewstoday.com/articles/309050.php