Tapeworms or cestodes are an ancient class of highly specialized flatworm parasites. Their ancestors diverged from free-living flatworms to parasitize the earliest vertebrates in Cambrian times, and subsequently followed all the complexities of vertebrate evolution so that there are now innumerable species subtly adapted to the behaviour, diet and immunology of their hosts. Most cestodes require at least two host species to support the different stages of their life cycles. Adult tapeworms inhabit the gut of a vertebrate animal (the definitive host), with four species adapted specifically to humans. The tapeworm consists of a scolex equipped with suckers, grooves (bothria) or hooks which are the means of attachment to the intestinal wall. This is connected by an actively growing neck region (the strobila) to a chain of a variable number of segments or proglottids which are …