See below. If the infection is parasitic, there are very few antibiotics (which generally for bacteria) that I can think of that would help at all. But they could create resistent bacteria in you body. For parasites, a antiparasitic med is needed.
Major? Your question raises a concern in my mind that the person may be a victim of scam called "Live Cell Analysis", in which they are shown their blood under a weird microscope and told that it's loaded with parasites. It's totally phony but it scares people. If I've guessed wrong, please forgive me.