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IX. Selected Diseases caused by Multicellular Animal Parasites. A. Diseases caused by Flatworms B. Diseases caused by Roundworms. IX. A. Diseases caused by Flatworms. Schistosomiasis Caused by the fluke Schistosoma
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IX. Selected Diseases caused by Multicellular Animal Parasites A. Diseases caused by Flatworms B. Diseases caused by Roundworms
IX. A. Diseases caused by Flatworms • Schistosomiasis • Caused by the fluke Schistosoma • Intermediate host: snails, in which the larval form of Schistosoma develops • The larvae are released into the water, and burrow into the skin of their human hosts (usually through feet or legs, while wading) • Many organs may be affected, including liver & lungs • The parasite reaches maturity in the human host and reproduces. Its eggs are released in the urine.
IX. A. Diseases caused by Flatworms • Tapeworms • Flatworms with segmented bodies • A head section with hooks (scolex) to attach to the intestinal wall • Multiple body segments (proglottids) that can number into the thousands • Each proglottid has a complete, functional reproductive system
IX. A. Diseases caused by Flatworms • Tapeworms (cont.) • Beef tapeworm (Taenia saginata) • Intermediate host: cattle • Embryonic form is transmitted to humans in contaminated pork • Adult worm develops in human intestinal tract and eggs are shed in feces • Eggs are eaten by cattle where they hatch & infect beef muscle to complete the cycle
IX. A. Diseases caused by Flatworms • Tapeworms (cont.) • Pork tapeworm (Taenia solium) • Intermediate host: swine • Fish tapeworm (Diphyllobothrium latum) • Intermediate host: Fish • Transmission similar to beef tapeworm
IX. B. Diseases caused by Roundworms • Ascariasis • Ascaris lumbricoides • Transmitted by ingestion of eggs in contaminated soil • Parasite grows and matures in the intestinal tract; eggs shed in feces • Pinworms • Enterobius vermicularis • Small roundworms, transmitted via contaminated soil in a similar manner as Ascaris • Painful itching around anus; often seen in small children
IX. B. Diseases caused by Roundworms • Trichinosis • Trichinella spiralis • Primarily transmitted via undercooked pork • The embryos develop in the intestinal tract and then travel to muscle tissue where they encyst • When the muscle tissue is eaten, the larval cysts hatch and complete their development in the intestinal tract of the next host