Exam #5: Cestode & Trematode Infection Flashcards
What are the characteristics of Cestodes?
Tapeworms
- Segmented bodies
- Hermaphoditic
- Absorb nutrients (no gut)
*Largest of the intestinal parasites (20-40 feet)
What are the characteristics of Trematodes?
Flukes
- Non-segmented
- Hermaphroditic
- Primitive gut
What are the three basic structures of adult tapeworms?
Scolex= rounded head of the worm, usually armed with hooks and suckers
Neck= area from which the new body segments are generated
Body (strobila)= a long segmented structure
What are individual segments of the strobila called? What is the importance of these structures?
- Proglottids
- Worms grow in length by generating new proglottids at the neck; thus, the most distal proglottids are the oldest
- Oldest proglottids are self-contained hermaphroditic structures that produce eggs (gravid)
- These gravid proglottids break off & are passed in feces
For which tapeworm infections are humans the definitive host?
Taenia saginota (beef tapeworm) Taenia solium (pig tapeworm)* Diphylobothrium lactum (fish tapeworm)
For which tapeworm infections are humans the intermediate host?
Echinococcus granulosus (dog tapeworm) Taenia solium (pig tapeworm)*
What is Taenia saginota? Describe the lifecycle of Taenia saginota.
Beef Tapeworm
- Cattle ingest eggs/ proglottids
- Larvae invade the circulation
- Encystation of larvae occurs in the muscle of the cow, called “cysticercus”
- Humans ingest undercooked meat containing cysts & the digestive process causes the release of cysticerci
- Scolex of the worm attaches to the intestines
*The worm will grow in the intestine until there is a mature adult tapeworm
What are the symptoms of Taenia saginota infection?
Generally asymptomatic
- Mild abdominal pain
- Feeling of fullness
*Note that infection can last YEARS and can grow up to 10-30 feet
How is Taenia saginota diagnosed?
Identification of proglottids or eggs passed by infected individual
What is Taenia solium? Describe the lifecycle of Taenia solium.
Pork tapeworm
- Lifecycle is essentially identical to beef tapeworm lifecycle
- Ingestion of encysted worm in pork muscle
*However, humans can become an intermediate host!
How do humans become an intermediate host of Taenia saginota?
- Ingested eggs hatch in the intestine & release larvae known as oncospheres
- Oncospheres burrow through the intestine & pass into circulation, where they encysts in the:
Lungs
Heart
Brain
Eye
Pathology develops because the parasite causes a space-filling lesion & because of the inflammatory response to the parasite.
Which is more common, beef or pork tapeworm?
Beef
What is the difference between intestinal & extraintestinal transmission of Taenia solium?
To get a pork tapeworm, you must EAT pork
To get systemic effects, must eat eggs of pork tapeworm, which can occur via human-human transmission
What is Cysticercus?
Extra-intestinal encystation of Taenia solium that creates a space filling lesion and induces localized inflammation
What is Neruocysticercosis?
A severe complication of extra-intestinal Taenia solium infection; encysts in brain
- Seizure
- Neurological defects
What is the presentation of Neurocysticercosis on MRI?
“Swiss cheese lesion”
How is intestinal Taenia solium diagnosed?
Proglottids or eggs in stool
How is extra-intestinal Taenia solium diagnosed?
Imaging
Serology
What is Diphyllobothrium latum?
Fish tapeworm
*This is the largest tapeworm to infect man
Describe the lifecycle of Diphyllobothrium latum.
- Eggs passed into water
- Egg hatches in water & is ingested by small fresh-water curstachains
- Crustachian is ingested by fresh-water fish
- Encystation of larvae occurs in the muscle of the fish
- Undercooked, raw, or pickled freshwater fish is then consumed by humans
What is the largest tapeworm infecting man?
Diphyllobothrium latum
How is Diphyllobothrium latum transmitted?
Ingestion of raw or undercooked fish
What are the symptoms of Diphyllobothrium latum infection?
Asymptomatic or mild
- Transient nausea, abdominal pain, diarrhea
- Infection with multiple worms can cause intestinal obstruction
- Macrocytic anemia due to Vitamin B12 deficiency may be seen in elderly
How is Diphyllobothrium latum diagnosed?
Eggs in stool
