You might not give them much thought, but parasites are everywhere. Estimates vary, but it’s likely that at least 40 percent of the species on Earth are parasites, and maybe as many as half.
A parasite is an organism that lives on or in another organism and lives at the expense of that organism. In other words, a parasite takes what it needs to survive from its host and gives nothing in return. Well, it can give quite a bit of suffering.
Not all parasites are deadly and disgusting, but some ghastly examples exist. Brain-eating amoebas, blood flukes, leeches, and the worms that cause lymphatic filariasis, also known as elephantiasis, are all parasites. So are bedbugs and lice. There are many kinds of parasites; some do more damage than others. The really bad ones can be very bad, and the big ones can be astonishing.
