IX Selected Diseases caused by Multicellular Animal Parasites

IX. Selected Diseases caused by Multicellular Animal Parasites A. B. Diseases caused by Flatworms 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