This Discovery Channel production investigates creatures that live on, and inside, the human body. How single celled parasites, multicellular parasites and worms are transmitted and proliferate is explained. Philip Coyne, Dickson Despommier, David Leiby and others outline recent problems with with cryptosporidium, Guinea worm, onchocerciasis ( river blindness ) and the plasmodium vivax virus, which causes malaria. Director Dilys Breese; narrator Terry McDonald.