Conclusion
The parasites presented here are only the tip of an ocean of infectious icebergs. There are more creatures out there besides flatworms. Consider the roundworms, the parasitic fungi: there's a whole wide world out there -- or should that be in there? Yes: in there. Wriggling, growing, breeding and feeding on your precious tissues and nutrients. Who knows how many organisms are in your guts right at this minute, having the time of their tiny lives? Why not introduce them to your campaign? As above, so below…