Figure 1

Life cycle of Spirometra erinaceieuropaei. (A) Unembryonated eggs are released and embryonate over 8 to 14 days in water [10]. (B,C) Eggs hatch to release free-swimming coracidia (B), which parasitize copepods (such as Cyclops sp.) and develop into procercoid larvae (C). (D) On ingestion of the copepod by a veterbrate host - such as a tadpole, frog or snake - these develop into plerocercoid larvae, also known as sparganum. The plerocercoid larvae reside in the tissues of these organisms. The larval stage infection can be passed on when the host organism is eaten. (E) Humans become infected by ingestion of a live larva, or in some cases direct contact, such as a poultice of infected frog tissue on the eye. A larva can also infect humans when an infected copepod is ingested. (F) The larva only develops into the adult form in the gastrointestinal tract once it reaches a definitive host, such as a cat or a dog, where eggs are passed in the faeces (A). Curly brackets denote known hosts, though the full extent of the possible hosts and life cycle complexity of this tapeworm species have not been well characterized. Images of S. erinaceieuropaei are guided by the experimental life history photographed by Lee et al. [10]. Source of modified images; snake [11]; frog courtesy of Anant Patel MD; cyclops [12] (Matt Wilson/Jay Clark, NOAA NMFS AFSC); dog [13] (Richard New Forest).