Diplozoon paradoxum is a flatworm parasite of fish. Eggs hatch and pass through larval stages where they swim to try to find a fish host. They attach to the gills of their host and develop further to the end of their diporpa stage. If a diporpa finds another diporpa, they can fuse to continue their development and maturation. If they don’t find one they die by the following winter. Fused parasites mature fully and begin to produce eggs, mainly in the summer months (1).
Schistosoma mansoni is a flatworm parasite of humans. Eggs hatch releasing miracidia that penetrate a snail. The parasite develops within the snail to become a cercaria capable of swimming. The cercariae are released from the snails and swim through the water to find a human. They penetrate through the skin of the human and lose their tail. They then migrate through the circulatory system to the liver where they complete their development. Adult males and females migrate to the veins near the GI tract to pair, mate, and lay their eggs. The eggs push through the tissue to end up inside the intestine to be shed with feces (2).
Taenia solium is a tapeworm of humans. Eggs in the environment that get eaten by pigs hatch in the pig's intestine. The resulting oncospheres penetrate through the intestinal wall and migrate to muscles where they develop into cysticerci. Humans that eat raw or undercooked pork that has cysticerci in it become infected. A cysticercus develops into an adult tapeworm that attaches to the small intestine, where it lives. The adults produce proglottids, which mature as they move down the length of the tapeworm. When fully mature, proglottids detach and are passed in the stool. The proglottids can contain up to 50,000 eggs each (3).
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Dr. Chenhua Li (Lead, Ideas), Dr. Þórey Jónsdóttir (Illustrator, Ideas), Stephen Pollo (Writer, Researcher), Yuanzhe Wang (Digital Consultant).