Answer: Echinococcus spp. adult worm. This small adult tapeworm is found in the intestine of canines - never humans. The eggs are released into the environment with the feces and normally infect herbivores such as sheep (E. granulosus) and rodents (E. multilocularis). When humans are unfortunate enough to ingest these eggs, they develop the cystic larval form in the liver and other organs. The larval stage is referred to hydatid disease and can be life-threatening since the cysts can attain large sizes, impinge on neighboring structures, and even rupture, releasing large amounts of anaphylaxis-inducing antigens.
Thank you to Alasdair who wrote in from The Gambia to answer this week's case! (Now that's dedication).