Cestodes, Platyhelminths (Tape Worms) Flashcards
General characteristics
Microscopic, hermaphodites, acolemate, bilaterally symmetrical, syncytial tegument, incomplete digestive, primitive kidney
Hypodermic impregnation, no specialized circ/resp system, cannot synthesize fatty acids/steroids
Anatomy: SCOLEX anterior end is head, encloses brain, may have hook, suckers, glands
Keratinous hooks for anchoring scolex, armed rostellum
Scolex suckers: acetabula, capu shaped, both Rita 2-6 shallow pits, bothridia muscular projections (ways of holding on)
Strobila: linear set of reproduction organs, each set proglottid
Stobiliation is process of proglottid appearing in anterior and maturing in posterior, body appears falsely segmented
Eggs are shelled embryos since they’re fertilized, gravid if present in proglottid
Diphylloboothrium latum
Broad-fish tapeworm
Characteristics: pickled/uncooked fish, life cycle requires two intermediate hosts, bilateral groove in scolex -> bothria
Life cycle:
1. Eggs in feces, free living coricidium larvae ingested by Diaptomus copepod
2. Procercoid larva develops 2-3 weeks, copepod eaten by minnow, pleurocercoid larva dev
3. Eaten by larger fish, pleurocercoid transferred or ingested
4. Eaten by definitive host (human), pleurocercoid den to immature adult attracted to SI by bothria
5. Adult tapeworm dev in SI, gravity segments appear in 20d, million thick yellow brown shelled eggs a day
Infection/symptoms: may be harmless, pernicious anemia
Treatment: Praziquantel, single dose outside US
Niclosamide and laxative from CDC
Sparganosis
D. Lactum larval form
Characteristics: drinking contaminated copepod water with procercoids, penetrates intestinal wall, comes to rest in muscles/subcutaneous tissue, grows into sparganum, can also come from eating tadpoles, snake or frog skin
Infection/symptoms: sparganum is wrinkled whitish ribbon shaped organism anywhere in body, serious painful inflammation at site of growth, crawling cysts or welts
Treatment: rare, surgical removal or Praziquantel
Dipyllidium caninum
Dog tapeworm
Humans become infected by ingesting fleas, infective stage is cysticercoid larva that lives in dog flea
Life cycle:
1. Gravity proglottids break off adult and pass in feces, packets of eggs held together by embryo membrane
2. Proglottids disintegrate in soil and release egg packets
3. Eggs ingested by flea larva, hatch in midgut, migrate to hemoceol
4. Hexacanth larvae become cysticercoid larvae, retained as flea develops to adult, flea must be ingested
5. Digested in host, release larva, attaches to SI, 25d to adulthood
Echinococcus granulosus
Hydatidiasis/Hydatid disease
Characteristics: AZ, NM, CA, most in liver or lung, developing cysts = brood capsules that break down to release protoscolices with granular material inside cyst called HYDATID SAND, can form in bone marrow
Life cycle:
1. Embryonated eggs pass feces of definitive host (dog), ingested by ruminates (sheep) or sometimes humans
2. Eggs hatch in SI to release on ops here (hexacanth larva), burrows through using 6 hooks to enter hepatic portal system
3. Cysts dev in liver for months, thin walled fluid filled cysts can reach 30cm
4. Protoscolices produced by budding of inner surface of germinal layer of bilateral cyst wall
5. Brood capsules form within cyst, each protoscolex form an adult worm in dog
6. Canines become infected when eating slaughtered sheep/reindeer entrails or flesh
7. Thousands of tiny worms may dev in dog intestine after eating single cyst, ungulates become infected through grazing on dog feces
Infection/symptoms: varies depending on location of cyst, liver most common, lung cysts can produce bloody or frothy sputum
Bursting cysts can lead to anaphylaxis
Treatment: surgical or Albendazole
Taenia Solium
Pork tapeworm and Cysticercosis
Characteristics: humans definitive hosts, pig intermediate, undercooked pork or humans dev cysticerci by consuming eggs from human feces, Mexico Latin America Slavic countries Africa, adult worm has muscular scolex with 4 acetabula and armed rostellum (double hooks)
Life cycle:
1. Ingest undercooked pork with cysticerus, pass to SI
2. Scolex evaginates and attaches to SI wall, tapeworm matures over 10-12 weeks, adult 4m in length
3. Proglottids break free and actively migrate out of anus, gravity proglottids have < 10 uterine branches
4. Enbryonated eggs ingested by intermediate host, hatch in SI, releases hexacanth larvae
5. Oncosphere penetrates intestinal wall/circulation, carried throughout body to dev into cysticerci over 3-5 weeks, now infective to humans
Infection/symptoms:
Adult tapeworm most infections asymptomatic, vague abdominal pain, hunger pain, chronic indigestion, eosinophilia
Cysticercosis prefer subcutaneous tissue (eye, brain, between muscle bundles), 2 mo to dev, commonly found in CNS, frequently become calcified, subcutaneous cysts palpable
Treatment: praziquantel or niclosamide
