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

2. 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.

3. 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

4. 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

5. 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

6. 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

7. 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