After I got back from Asia 12 years ago, I was feeling bad and having gut problems. My general doctor tested me and the test found Giardia. I took Antibiotics and improved.
However, the standard test missed schitsosomiasis. I have had it inside me, eating my blood and laying eggs in me for 12 years! The symptoms were worse on full moons. I was able to catch it by taking stool samples after the days I felt bad (right after the full moon) and sending it to a good lab that could diagnose its eggs. I am finally getting treatment this week!