Cestodes and Trematodes

Taenia spp

Tapeworm parasites that infect humans and animals.

Cestodes

A class of parasitic flatworms commonly called tapeworms.

Taenia solium

Pig tapeworm that can cause taeniasis and cysticercosis.

Taenia saginata

Beef tapeworm that causes taeniasis.

Pig.

Common host of T. solium

Cattle.

Common host of T. saginata

Humans only.

Definitive host of Taenia species

Scolex of T. solium

Has four suckers and a rostellum with hooks.

Scolex of T. saginata

Has four suckers but no hooks or rostellum.

Gravid proglottids of T. solium

Has 5 to 10 primary uterine branches.

Gravid proglottids of T. saginata

Has 15 to 25 primary uterine branches.

Taeniasis

Infection of humans with the adult Taenia tapeworm.

Source of taeniasis

Eating raw or undercooked infected pork or beef.

Infective stage of Taenia to humans

Cysticercus in meat.

Eggs of Taenia

Passed in feces and can survive days to months in the environment.

Oncosphere

Larval form that hatches from Taenia egg in animals.

Where oncospheres migrate

Striated muscles of pigs or cattle.

Cysticerci

Larval cyst stage found in animal muscles.

Where adult Taenia lives

Small intestine of humans.

Attachment organ of adult Taenia

Scolex.

Length of T. saginata

Usually 5 meters or less but may reach 25 meters.

Length of T. solium

About 2 to 7 meters.

Symptoms of taeniasis

Usually mild intestinal symptoms.

Neurocysticercosis

Brain infection caused by T. solium larvae.

Symptoms of neurocysticercosis

Seizures and obstructive hydrocephalus.

Diagnosis of Taenia infection

Direct fecal smear showing eggs or proglottids.

MRI for Taenia

Used to detect neurocysticercosis.

Diphyllobothrium latum

Fish tapeworm and longest human tapeworm.

Common source of D. latum infection

Eating raw or undercooked fish.

Scolex of D. latum

Has two elongated sucking grooves called bothria.

Proglottids of D. latum

Wider than long.

Eggs of D. latum

Passed unembryonated in feces.

Coracidia

Free-swimming larval stage that develops from eggs in water.

First intermediate host of D. latum

Crustacean.

Larva in first host

Procercoid larva.

Second intermediate host of D. latum

Small fish.

Larva in fish

Plerocercoid larva or sparganum.

Infective stage of D. latum to humans

Plerocercoid larva in fish muscle.

Paratenic host

Larger predator fish carrying infective larvae.

Where adult D. latum lives

Small intestine.

Length of adult D. latum

More than 10 meters.

Number of proglottids in D. latum

More than 3

Egg production of D. latum

Up to 1

Diphyllobothriasis

Infection caused by Diphyllobothrium latum.

Symptoms of diphyllobothriasis

Mild intestinal symptoms.

Major complication of D. latum

Vitamin B12 deficiency causing megaloblastic anemia.

Other effect of D. latum

Malnutrition.

Diagnosis of D. latum infection

Direct fecal smear showing eggs or proglottids.

Schistosoma spp

Trematode blood flukes that cause schistosomiasis

Trematodes

Class of parasitic flatworms known as flukes

Schistosoma japonicum

Blood fluke with small lateral spine on egg

Schistosoma mansoni

Blood fluke with large prominent lateral spine on egg

Schistosoma haematobium

Blood fluke with terminal spine on egg causing urinary schistosomiasis

Endemic areas (Philippines)

Sorsogon Samar Leyte Oriental Mindoro Bohol all of Mindanao except Misamis Oriental

Trematode

Parasitic flatworm group called flukes

Infective stage of Schistosoma

Cercariae that penetrate human skin

Diagnostic stage of Schistosoma

Eggs found in feces or urine

Definitive host

Humans

Intermediate host

Snail Oncomelania quadrasi

Mode of transmission

Skin penetration by cercariae in contaminated water

Miracidium

Free-swimming larva that infects snail

Sporocyst

Stage inside snail that produces cercariae

Cercariae

Infective larval stage that penetrates skin

Schistosomulae

Stage after cercariae enter human skin

Migration route

Skin blood lungs heart liver mesenteric veins

Adult worm location S japonicum

Superior mesenteric veins small intestine

Adult worm location S mansoni

Inferior mesenteric veins large intestine

Adult worm location S haematobium

Vesical and pelvic venous plexus bladder

Egg release

Eggs exit via feces or urine depending on species

Schistosomiasis

Disease caused by Schistosoma infection

Cercarial dermatitis

Itchy skin rash from cercariae penetration swimmer’s itch

Katayama fever

Acute allergic reaction to Schistosoma infection

Liver granulomas

Inflammation around trapped eggs in liver

Painless hematuria

Blood in urine seen in S haematobium infection

Diagnosis Kato-Katz

Fecal exam showing Schistosoma eggs

COPT test

Blood test detecting circulating Schistosoma antigen