Spirometra tapeworms have a complex multi-host life cycle in which the definitive host (i.e., the host in which the parasite matures and reproduces) is a dog or cat. However, although humans cannot serve as definitive hosts for Spirometra tapeworms, they can serve as paratenic hosts ("transport hosts") or second intermediate hosts and develop sparganosis. Humans acquire sparganosis by either drinking water contaminated with infected copepods or consuming the flesh of an under-cooked second intermediate or paratenic host. Larvae of these tapeworms (spargana) can live up to 20 years in the human host.
Spirometra species known to infect humans and cause sparganosis include S. mansoni, S. ranarum, S. mansonoides, S. erinacei, and the related Sparganum proliferum (with ambiguous taxonomic affinities).
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