Helminths - Cestodes Flashcards
General characteristics of helminths:
Acoelomates - No body cavity. Flat, segmented chains. Monoecious - Both sexes in one segment. Each segment is reproductively independent. Adults usually in SI. Usually non-pathogenic.
Cestode segments are called:
Proglottids.
The anterior end of the cestode is called:
The scolex. This is the “holdfast organ”
Types: Acetabula (suckers) and Bothria (slit-like)
What type of life cycle do cestodes follow? DIrect or indirect?
Indirect!
What are the two important orders of cestodes?
Cyclophyllidea and Diphyllobothriidea
General characteristics of Cyclophyllidea:
“True” cestodes. Terrestrial. ONE IH, which could be many vertebrates. Acetabula scolex. Eggs in gravid proglottids.
General characteristics of Diphyllobothriidea:
“Primitive” cestodes. Aquatic. Require TWO IHs. 1st IH = copepod. 2nd IH is freshwater fish or vertebrates. Bothria scolex. Eggs are expelled from adults.
What is a metacestode?
Larval cestode in IH and more often associated with disease.
What is a procercoid?
Name for the Diphyllobothriidea in the first IH.
What is a plerocercoid?
Name of the Diphyllobothriidea in the 2nd IH.
Taenia pisiformis:
Most common cestode in dogs. Inverted scolex (inside worm). Proglottids are shed in feces. Larval type: cysticercus IH - rabbits, commonly in the liver. DH - dogs
Taenia hydatigena:
Proglottids shed in feces.
Larval type: cysticercus
IH - ruminants/swine, commonly in peritoneum.
DH - dogs.
Taenia taeniaeformis:
The only one in the cat!
Larval type: strobilocercus
IH - usually rodents.
DH - cat
T. multiceps and T. serialis:
Enter sheep brains and cat brains respectively.
T. solium and T. saginata:
Pork tapeworm and Beef tapeworm respectively.
Humans may become accidental IH of solium, but not saginata. Humans can self-infect!
Echinococcus spp.
Adults are xtremely small - will not see on necropsy.
Metacestodes are large
Form hydatid cyst, which can be unilobular or multilobular.
Echinococcus granulosus:
Different strains which infect different IHs.
IH - ungulates
DH - dogs
Usually no pathology!
Unilocular hydatid cysts form in liver and lungs.
ZOONOTIC RISK!
Ecchinococcus granulosus sylvatic vs domestic life cycle:
Sylvatic - “wild type” infection. IH - caribou, DH - wolves **Predator/prey life cycle”.
Domestic - In domestic animals. IH - Sheep and other ungulates, DH - dogs.
Ecchinococcus multilocularis
Northern hemisphere, colder climates.
Sylvatic cycle most likely.
IH - rodents. If dog eats feces, can become IH.
DH - foxes, coyotes, other canines, rarely cats.
Not as zoonotic as E. granulosus.
Pathology mimics hepatic carcinoma (abdomen) w/ multilocular hydatid cyst.
