Week 3 - Cestode Parasites of the GIT

What type of life-cycle do tapeworms have?

Two host life-cycle

• Larval stage in Intermediate host

• Adult stage in Final host

Features of tapeworms

• Adults nearly always in SI of final host (where sexual reproduction occurs)

• Attach using head, which has suckers and sometimes hooks

• Adult body = flat & segmented

Unique features of adult tapeworms

• No alimentary tract

• Absorb nutrients across the surface

• Hermaphrodite

• Each segment contains male & female

• Segments at tail end are "gravid" (contain only eggs)

What is the biggest tapeworm?

• Taenia saginata - the beef tapeworm

• Can reach 5-15 meters

• Found in SI of humans

• Transmitted by consumption of undercooked beef containing cysts

Basic tapeworm life-cycle

Adults in SI -> gravid segments shed from worm, pass in feces, contains eggs -> ingested by intermed host, embryo released from egg in IMH -> larva settles down & encysts -> cysts ingested by final host -> head of worm released & latches onto wall of SI

Important tapeworm species

• Taenia saginata: FH: human, IMH: bovine

• Taenia solium: FH: human, IMH: pig/human

• Echinococcus granulosus granulosus: FH: dog, IMH: ruminants, pigs, humans

T. saginata epidemiology

• Eggs are resistant & long lived

• Infection occasionally seen in several cattle

• Cysticercosis "storms"

• Associated with use of human sludge as fertilizer

• Ingestion of undercooked beef

T. saginata diagnosis & control

Diagnosis:

• Finding cysts in meat

Control:

• Restrict use of human sludge to arable fields or do not allow cattle to graze for 2 yrs

• Hygiene/sanitation

• Meat inspection, condemn infected carcass

• Cook meat properly

T. solium pathology

• Adult = little pathology in SI

• Cysts in CNS or eye

• Major problem in S. America

T. solium epidemiology

• Close association man/pig

• Unrestricted access of pigs to human waste

• Poor/no meat inspection

T. solium control

• Treat humans to kill adult worms

• Health education

• Mass treatment of pigs

• Meat inspection

• Pig corralling

• Vaccination

E. g.granulosus epidemiology

• Dog FH infected from eating meat with cyst

• Sheep IMH infected by eating contaminated dog feces

• IMH depends on local animal husbandry

E. g.granulosis pathogenesis

• Dogs can have thousands of worms and show no clinical signs

• Hydatid cyst well tolerated in IMH

• Hydatid cyst detected in abattoir

• Always of significance in humans

Control of hydatid disease

• Regular deworming of dogs

• Proper disposal of infected carcasses

• Deny access of dogs to abattoirs

• Hygiene

• Vaccine in works (varied results)

Dipylidium caninum

• Common in strays

• fleas & lice are IMH

• Active motile segments

• Double genital pore

• Eggs in egg packets (contain 20 eggs)

• Need to treat ectoparasites as well as adult worms