Parasitology: Cestodes

Flat, segmented worms lacking a digestive tract

Cestodes

External body covering specialized for nutrient absorption

Tegument

Head region with attachment organs

Scolex

Reproductive segments of tapeworms

Proglottids

Terminal gravid segment passed in stool

Gravid proglottid

Host containing larval cyst stage

Intermediate host

Infective stage for humans in most cestodes

Cysticercus (larval stage)

Larval form with fluid-filled bladder and invaginated scolex

Cysticercus

Structure used to differentiate Taenia species eggs

None. Cannot be differentiated (eggs identical)

Mode of nutrition in cestodes

Absorption through tegument

Beef tapeworm

Taenia saginata

Intermediate host of Taenia saginata

Cattle

Scolex without hooks

Taenia saginata

Proglottids actively motile in stool

Taenia saginata

Uterine branches count (>15)

Taenia saginata

Taenia saginata Infection from ingestion of

Undercooked beef

Taenia saginata Does NOT cause cysticercosis (T/F)

True

Taenia saginata Length (can reach up to)

10-25 meters

Rare complication of Taenia saginata

Intestinal obstruction

Diagnostic stage of Taenia saginata in stool

Eggs or proglottids

Pork tapeworm

Taenia solium

Scolex with hooks and suckers

Taenia solium

Intermediate host of Taenia solium

Pig

Infective stage of Taenia solium for cysticercosis

Eggs

Taenia solium Disease caused by larval stage in brain

Neurocysticercosis

Autoinfection mechanism of Taenia solium

Reverse peristalsis or fecal-oral

Uterine branches count (<15)

Taenia solium

T. solium is more dangerous than T. saginata because

Causes cysticercosis

T. solium location of adult worm

Small intestine

T. solium imaging finding in neurocysticercosis

Calcified cysts (“starry sky”)

Cysticercosis caused by larval stage of

Taenia solium

Cysticercosis most common site in humans

Brain

Brain imaging description of neurocysticercosis

Starry sky

Cysticercosis mode of transmission

Ingestion of eggs

Most serious complication of cysticercosis

Seizures

Cysticercosis subcutaneous nodules contain

Cycsticerci

Ocular cysticercosis leads to

Vision loss

Viable cysts of cysticercosis show what feature

Scolex inside cyst

Cysticercosis treatment drug of choice

Albendazole

Cysticercosis inflammatory reaction occurs when

Cyst degeneration

Fish tapeworm

Dyphyllobothrium latum

Largest human tapeworm

Diphyllobothrium latum

Intermediate hosts (2 required) of D. latum

Copepod + fish

Infective stage of D. latum

Plerocercoid

D. latum associated vitamin deficiency

Vitamin B12

Type of anemia produced in D. latum

Megaloblastic anemia

Operculated eggs

Diphyllobothrium latum

Transmission of D. latum via

raw fish

Scolex characteristic of D. latum

Bothria (grooves)

Geographic association of D. latum

Cold freshwater regions

Dwarf tapeworm

Hymenolepis nana

Only cestode that can complete lifecycle in one host

Hymenolepis nan

Infective stage of H. nana

Egg

Mode of autoinfection of H. nana

Internal autoinfecction

H, nana eggs contain

Polar filaments

H. nana common in children (T/F)

True

H. nana Intermediate host required?

No

H. nana cause of heavy infection

Autoinfection

H. nana transmission route

Fecal-oral

H. nana diagnosis

Eggs in stool

Rat tapeworm

Hymenolepis diminuta

Intermediate host of H. diminuta

Fleas/ Beetles

Eggs of H. diminuta lack

Polar filaments

Humans get infected by H. diminuta by ingestion of

Infected arthropods

H. diminuta less common than H. nana (T/F)

True

Definitive host of H. diminuta

Rats

H. diminuta size compared to H. nana

Larger

H. diminuta Infection severity

Mild

H. diminuta typical host environment

Rodent-infested areas

Diagnostic stage of H. diminuta

Eggs

Dog tapeworm

Echinococcus granulosus

Disease caused by E. granulosus

Hydatid Cyst

Definitive host of E. granulosus

Dog

Intermediate host of E. granulosus

Sheep

Infective stage of E. granulosus to humans

Eggs

Hydatid sand of E. granulosus refers to

Protoscolices

E. granulosus cyst rupture leads to

Anaphylaxis

In E. granulosus, liver is most common site (T/F)

True

E. granulosus daughter cyst formation present or absent?

Present

Imaging sign of E. granulosus

Floating membranes

Causes alveolar hydatid disease

Echinococcus multilocularis

E. multilocularis more invasive than E. granulosus (T/F)

True

E. multilocularis mimics what disease

Malignancy

Geographic distribution of E. multilocularis

Northern hemisphere

Definitive host of E. multilocularis

Fox

Growth pattern of cyst of E. multilocularis

Infiltrative

E. multilocularis prognosis compared to E. granulosus

Worse

E. multiloculris organ primarily affected

Liver

Mode of spread of E. multilocularis

Invasive spread

E. multilocularis surgical resectability

Often unresectable

Operculated eggs belong to

Pseudophyllidea

Non-operculated eggs belong to

Cyclophyllidea

Presence of uterine pore

Pseudophyllidea

Eggs released via gravid proglottids

Cyclophyllidea

Bothria vs suckers difference

Bothria (grooves) vs suckers

Lifecycle requiring 2 intermediate hosts

Diphyllobothrium latum

Lifecycle requiring 1 intermediate host

Taenia spp.

Example of pseudophyllidean cestode

Diphyllobothrium latum

Example of cyclophyllidean cestode

Taenia solium

Absorption of nutrients occurs via

Tegument