Cestodes Flashcards
Cestoda
Phylum: platyhelminthes
- acoelomates
- dorsoventrally flattened
- segmented
- monoecious
- adults in DH small intestine
Are adult cestodes pathogenic?
Not usually
- larval stages are pathogenic
Proglottids
Cestode segments
- immature segments are toward the head, as they move over they mature
- gravid segments are located toward the end, contain eggs
Cestode body
Stroblia
- chain of independent reproductive units (proglottids)
Scolex
Anterior end of cestode
- holdfast organ
- may have specialized attachement organs
- acetabula (suckers, usually have 4)
- bothria (2 slits on either side for loose attachement)
- bothridia
Cestode eggs typically contain the ______
First larval stage
- eggs come in various morphologies
Cestodes have an _____ life cycle
Indirect!
- DH (predator) with cestode in SI –> proglottids with eggs in feces –> eggs in environment ingested –> IH (prey) with metacestode (larval stage) in tissues –> IH ingested
Which stage is infective to the DH?
Metacestode
Does the DH have to be a predator?
No, the IH could be free living mites in the environment (how horses get infected)
Cyclophyllidea
True cestodes
- terrestrial life cycle
- cestode larvae require 1 IH
- IH: various vertebrates and invertebrates
Diphyllobothriidea
Primitive cestodes
- aquatic life cycle
- cestode larvae require 2 IH
- first IH: copepod
- second IH: fish or non-fish vertebrate
Difference between 2 genera
Look at ppt!!
Metacestode
Larval cestode in IH
- metacestodes are more often associated with disease than adult cestodes!!
How many metacestodes do cyclophyllideans have?
6 types, depends on species!
- metacestodes that develop into 1 adult DH: cysticercus, strobilocercus, cysticercoid
- metacestodes that develop into multiple adults in DH: coenurus, unilocular hydatid cyst, alveolar (multilocular) hydatid
How many metacestodes do diphyllobothriideans have?
2 stages, depends on IH
- procercoid develops in first IH
- plerocercoid develops in second IH
- each plerocercoid develops into 1 adult cestode!*
Cysticercus
Bladder worm
- small, fluid filled scolex inside
- ex: Taenia pisiformis
Strobilocercus
Fluid filled bladder, but scolex is everted!
- resembles a cyst in adult animal
- ex: Taenia taeniaeformis
Cysticercoid
Solid, scolex inside
- cestodes with arthropod IH
- ex: Dipylidium caninum, Anoplocephalids
Coenurus
Multiple larvae attached in cyst
- ex: Taenia multiceps
Unilocular hydatid cyst
Cysts in cysts, internal budding
- thick walled, slow growing
- ex: Echinococcus granulosus
Alveolar (multilocular) hydatid
External budding
- thin walled, invasive, faster growth
- ex: Echinococcus multilocularis
Endogenous budding
Slow growing
- thick walled
Exogenous budding
Fast growing
- thin walled
Procercoid
First larval stage
- found in 1st IH
Plerocercoid
Second larval stage
- found in 2nd IH
Taeniidae
Taenia, Echinococcus
- DH and IH are mammals!
- predator/prey
- adult cestodes in DH small intestine
- metacestodes in IH may cause disease
- humans may be DH or dead end IH (zoonotic!)
What is the treatment of choice for Taeniidae?
- praziquantel
- epsiprantel
- fenbendazole (Taenia pisiformis)
Taenia pisiformis life cycle
DH (canids) cysticercus is digested –> scolex embeds in SI –> develops into adult –> proglottids shed in feces –> IH (rabbit), egg ingested, hatches –> hexacanth embryo migrates to organ –> develops into cysticercus (metacestode)
Where is the cysticercus located in the IH of Taenia pisiformis?
On the liver/mesentery
Taenia hydatigena life cycle
DH (canids) –> cysticercus is digested –> scolex embeds in SI mucosa –> develops into adult –> proglottids shed in feces –> not as common as T. pisiformis in domestic dogs –> IH (ruminants, swine), cysticercus in peritoneal membranes
Taenia taeniaeformis life cycle
DH (felids) –> strobilocercus is digested –> scolex embeds in SI mucosa –> develops into adult –> proglottids shed in feces –> IH (rodents), strobilocercus in liver, peritoneum
Taenia multiceps coenurus is located in the ______
Sheep brain
Taenia serialis coenurus is located in the _______
Cat brain
Which 2 species of Taenia have public health importance?
- Taenia solium (pork tapeworm)
- Taenia saginata (beef tapeworm)
Taenia solium life cycle
DH (humans) –> proglottids shed in feces –> IH (swine) cysticercus in muscle –> DH ingests IH, or becomes accidental IH via ingesting eggs
Taenia saginata life cycle
DH (humans) –> proglottids shed in feces –> IH (cattle), cysticercus in muscle
no chance of humans becoming accidental IH, ingested eggs do not develop
Taenia solium cysterceri are located in ______
Various locations
- subcutaneous, eyes, etc
- neurocysticercosis: prevalence of epilepsy
Taenia solium and Taenia saginata prevalence
Endemic foci throughout the world
- high prevalence of infected pigs
- high risk factors for human infection
Echinococcus spp
- small adult stages (several mm long, 3-5 segments)
- metacestodes are very large! –> unilocular or multilocular hydatid cysts
- zoonotic!!
Echinococcus granulosus life cycle
DH (canids) –> hydatid is digested –> scolices embed in SI mucosa –> develop into adults –> eggs in feces –> IH (primarily ungulates), unilocular hydatid cyst in liver, lung, etc
Echinococcus granulosus - sylvatic cycle
Wolf (DH) –> caribou (IH) –> dingo (DH) –> kangaroo (IH)
- other DH: coyotes
- other IH: moose
Echinococcus granulosus - domestic cycle
Dogs (DH) –> sheep (IH)
- other IH: swine, cattle, horses
Distribution of E. granulosus in US
Common in sheep herding areas
E. granulosus - zoonosis
Humans are accidental IH
- ingest eggs while handling dogs
- benign neoplasia, cystic echinococcosis
- endemic in Australia, Africa, S. America
Echinococcus multilocularis life cycle
DH (foxes, other canids, rare in cats) –> hydatid is digested –> scolices embed in SI –> develop into adults –> Taeniid eggs in feces –> IH (rodents) –> multilocular hydatid cyst in abdominal cavity
Echinococcus multilocularis - sylvatic cycle
Arctic fox (DH) –> vole (IH)
- other DH: wolves, other foxes
- other IH: lemmings, other rodents
- sylvatic is the primary cycle!!
Echinococcus multilocularis - domestic cycle
- other DH: dogs, cats (rare)
- other IH: rodents (rarely, cattle, horses, swine)
E. multilocularis prevalence
Endemic to northern hemisphere
E. multilocularis zoonosis
Humans are rarely an accidnetal IH
- pathology mimics hepatic carcinoma
- alveolar echinococcosis/hydatid disease
Diplylidium caninum
Cucumber tapeworm, flea tapeworm, double pored tapeworm
- DH: felids and canids –> infection by ingestion of infected IH, rarely causes pathology in DH
- IH: Ctenocephalides felis, other fleas, Trichodectes canis
- zoonotic*
Dipylidium caninum life cycle
DH (canids, felids) –> proglottids shed in feces –> egg packet –> flea larva ingests eggs –> IH (adult fleas), biting lice –> cysticercoid –> DH ingests flea
How do diagnose D. caninum
Based on visualization of characteristic proglottids and/or egg packets in feces
- usually includes a history of flea ingestion
- animal can still be infected if on a monthly flea control!
Anoplocephala perfoliata
DH: equids - ileum, cecum, ileocecal junction - 4 lappets under suckers - associated with colic, inflammation, ulcers IH: oribatid (free living) mites
Anoplocephala perfoliata life cycle
DH = equids –> proglottids and eggs shed in feces (eggs in low numbers, segments easily missed) –> egg has pyriform apparatus –> IH = oribatid mite –> cysticercoid
Anoplocephala magna
- life cycle similar to A. perfoliata
- posterior SI
- larger than A. perfoliata, no lappets
- relatively harmless
Paranoplocephala mamillana
- life cycle similar to A. perfoliata
- anterior SI
- smaller than A. perfoliata, no lappets
- relatively harmless
Moniezia life cycle
DH (ruminants) –> proglottids shed in feces (pyriform apparatus) –> IH (oribatid mites) –> cysticercoid
Are Moniezia pathogenic?
NO
- very common
Thysanosoma life cycle
Fringed tapeworm
- DH (small ruminants, rarely cattle and deer) –> adult cestodes in bile duct and duodenum –> proglottids shed in feces –> egg packets similar to D. caninum –> IH (booklice or bark lice) –> cysticercoid
Thysanosoma prevalence
- western north and south america
- mountain areas
Spirometra life cycle
DH (felids, bobcat, canids, raccoons) –> eggs shed thru central uterine pore (operculated) –> coracidium (aquatic habitat) –> 1st IH (copepod) –> procercoid –> plerocercoid (sparganum) –> 2nd IH (non fish vertebrates) –> could also be paratenic hosts
Spirometra spp
- common in southeastern US (Spirometra mansonoides)
- adult cestodes associated with GI signs in dogs and cats (vomiting, diarrhea, weight loss)
Sparganosis
When the plerocercoid causes disease
- humans may become accidental 2nd IH via ingestion of copepod with procercoid, or PH via ingestion or transfer of plerocercoid
- could be ocular, SC, CNS, auricular, pulmonary
What if a cat ingests copepods with the procercoid?
Cat becomes the 2nd IH with development of sparganosis
Diphyllobothrium latum life cycle
DH (canids, felids, humans) –> eggs shed thru central uterine pore –> coracidium (aquatic habitat) –> 1st IH (copepod) –> procercoid –> 2nd IH (freshwater fish) –> plerocercoid –> PH (hosts other than fish)
Diphyllobothrium latum prevalence
- distribution: cold climates, northern US
D. latum human infection
No or mild clinical disease
- acute: GI symptoms
- chronic: vitamin B12 deficiency –> nerve degeneration
Cyclophyllidean segments
- mesocestoides and echinococcus: tiny proglottids, will not see grossly
- dipylidium: proglottids tapered on ends
- taenia: proglottids rectangular in shape
Adult _____ cestodes are more likely to cause disease
Diphyllobothriidean
Which 2 adult cyclophyllideans do cause disease?
- anoplocephala perfoliata
- thysanosoma
Pathogenesis of metacestodes in IH depends on ______
- location
- size
- invasiveness
Name of pathogenesis of Diphyllobothriidean metacestodes in 2nd IH
Sparganosis
What is NOT a viable form of treatment for cestodes?
Avermectins/milbemycins
Control
- flea control (vacuuming)
- prevent predator/prey behavior
- pasture management to decrease mite populations and contamination by feces with cestode eggs
Humans as accidental IH (4)
- echinococcus granulosus
- echinococcus multilocularis
- spirometra spp (2nd IH or PH)
- taenia solium
Humans as accidental or normal DH (4)
- dipylidium caninum (accidental)
- taenia solium
- taenia saginata
- diphyllobothrium latum
