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