Lab session 4

Helminths

Worms

• Platyheminthes (flatworm)• Nematodes (roundworms)• 2 types platyhelminthes• Trematodes (flukes)• Cestodes (tapeworms)• Flat body, hermaphroditic – both male and

female reproductive organs• Both testes and ovaries

• Complex life cycle

• Intermediate host – larvae of the worm (immature worm), asexual reproduction takes place

• Definitive host – adult worm (mature worm), sexual reproduction takes place.

• Flukes – flat leaf like body

• hermaphroditic

Clonorchis sinensisChinese liver fluke

• Adult worm – bile ducts of humans• Eggs are released in the feces• When it reaches a body of water larva comes

out• Ingested by a specific species of snail• Asexual reproduction takes place• Larvae come out of the snail• Penetrates a fish and forms a cyst in the fish• When people eat undercooked, contaminated

fish larvae end up in the bile ducts• Develop into adult worms• Cycle continues

• Diagnosis is based on the presence of eggs in the feces.

OperculumLid-like structure

Flower vase

Cestodes (tapeworms)

• Scolex – head

• Segmented body

• Segment – proglottids

• Hermaphroditic

• Each proglottid has testes and ovaries

Taenia saginta (beef tapeworm)

• Adult – human intestinal tract• Eggs are released in the feces• Ingested by cattle• Larvae come out in the intestinal tract• Cysts in the muscle• Cyst (sleeping, resting larva)• Undercooked, contaminated meat ingested by humans• Scolex comes out of the cyst• Attaches to the intestinal wall• Makes proglottids

• All tapeworms make identical eggs

• Taenia pisiformis

Nematodes (roundworms)

• Dioecious

• Male and female worms

Entirobius vermicularis (pinworm)

• Intestinal tract of humans• Female worm comes out of the anus• Releases its eggs• Eggs – clothing, bedding, airborne• Ingested by another host• Eggs reach intestinal tract• Larvae come out• Grows into an adult worm• Intense itching in the perianal area

flat More curved

Larva curled up

Ascaris lumbricoides

• Adult – intestinal tract• Eggs released in the feces• Ingested in contaminated food and water• Larvae come out in the intestinal tract• Grow into adult worms• Eat semidigested food• Blockage (obstruction) of the intestinal

tract.

Irregular surface

Necator americanusHookworm

• Adult – intestinal tract• Eggs – feces• Larvae come out in the soil• When people step on them, they penetrate the skin• Migrate to the intestinal tract• Attach to the intestinal wall• Feed on blood• Grow into adult worms• Anemia • Wearing shoes

Trichuris trichurawhipworm

• Adult – intestine

• Eggs – feces

• Contaminated food or water

• Larvae come out in the intestinal tract

• Bloody diarrhea

Football shaped

eye

Trichinella spiralis

• Transmitted in contaminated, undercooked• Encysted pork• Larvae come out of the cyst in the

intestinal tract• Grow into adult worms• Female releases larvae• From cysts in the muscle• Diaphragm muscle