Humans / mammals in general are loaded with parasites of all sizes......they can be inside a tooth by the thousands, as well as inside the smallest of nerves.......
As long as humans can not see them---they generally ignore them and give them endless medical diagnoses disease names.
One thing humans can not endure is to see skin parasites------just seeing 1 or a few is bad enough, but if they see them wriggle up and out by the dozens or hundreds, that is more than the human brain can tolerate. There are videos of people that through various methods remove worms from their skin and those people become so paranoid that they can not stop--it is not something the eyes / brain can forget. That and if the person does nothing to kill them internally, good chances they will continue to always see worms come up and out.
There is an herbal method that you apply to the skin and watch the worms appear....I would just call the little critters pin worms and many worms are too small to see with the eyes. I encouraged 1 Chinese herbal company to investigate such a formula and they found it in an ancient Chinese writing and had trouble finding the key ingredient, but eventually made it about 3 years ago and said it works 50% of the time on animals. They have never said if they have tried it with humans..........it would be a dream come true herbal product, just for the fact that if you gave some to a human and they applied it to their arms and seen worms---they would forever believe that humans have worms. Otherwise I assume 90+% of the world population never gives worms a second thought, that is just something farm animals get.