Parasitic worms (Helminths) (Ch.12)

Cestoda (tapeworms)

-Are hermaphroditic (having ovaries and testes (being both sexes at the same time) -Head is scolex; segments are proglottids *Tapeworm life cycle has 2 hosts -Intermediate host: Infected by ingestion tapeworm eggs; contains larva cyst in skeletal muscle and other organs such as brain (infection is called cysticercosis) -Definitive host: Infected by ingesting larval cyst; adult tapeworm grows in intestine. Ex: Dogs Examples: Tania saginata= beef tapeworm Tania solium=pork tapeworm

2. Aschelmenthes or Nematoda (roundworms)

-Cylindrical and tapered at each end -Males are smaller than females -Plain, unsegmented worms ranging from microscopic up to about 12 inches Ex: Ascaris spp

Trematode (flukes)

-Have a leave shape -Are parasitic -Have complex life cycles with several larval forms Lava= an immature form of an animal; doesn't look like the adult. Cycle has an intermediate host and definitive host -Are hermaphroditic= having both ovaries and testes Ex: Conorchis sinensis (Chinese liver fluke) and Shistosoma (Blood flukes) male and female

List the defining characteristics of parasitic helminths

-Kingdom Animalia: Eukaryotic -No cell walls -Heterotrophic nutrition -Specialized tissues -Live inside their hosts -May have a digestive system -Have reduced nervous system -Have complex reproductive systems -Have 2 phyla

1. Phylum Platylhelminthes (flatworms) divides into

1. Trematoda (flukes) 2. Cestoda (tapeworms)

Intermediate host

An organism that harbors the larval stage of a Helminth or protozoa.

Definitive host

An organisms that harbors the adult, sexually mature form of a parasite.

Ascaris spp

Cause ascariasis (intestinal infection) -The largest roundworms are up to 12 in. - 1/4 of world's population infected -Infection by ingesting worm eggs that can remain in the soil 10 years Examples: 1. Ascaria lumbricoides 2. Trichinella spiralis -Cause Trichinosis (larval cyst in skeletal muscle). -Infection by ingesting larval cysts in under cooked pork or beef meat. 3. Wucheraria bancroft -Causes filariasis (worms in lymphatic vessels) -Microfilaria larva transmitted by Culex spp. mosquitoes -Grow to adults 2-3 inches long -Block flow of lymph -If untreated, after years of infestation, leads to elephantiasis (swelling due to accumulation of fluid in tissue)

Schistosoma haematobium

Causes Schistosomiasis Portal of entry: Skin Source of infection: Larvae from fresh water snails Disease is not contracted in US. Immigrants have it! Lives primarily in the pelvic veins Snails are the intermediate host

Provide a rationale for the elaborate life cycles of parasitic worms

The anatomy and life cycles of parasitic Helminths are modified for parasitism.