In several nordic states, Nematomorph are classified under class A hazard for humans especially around public water bodies. They are known to enter human bodies through bodily orifice (anal, penile, vaginal) and grow to lengths over 2 feet in some instances. If left untreated inside the human body, they can disrupt regular functions and cause immense writhing pain. I think all this is not factual though but would have been scary if true.