6.8 Cestodes - Tapeworms Flashcards
What are cestodes
tapeworms
what is the head of a tapeworm called? what about the chain segments
the scolex; the strobia
Cestodes are typically highly host-specific/nonspecific
host-specific
what is the effect of cestodes on the intermediate host vs definitive host
usually not pathogenic as adults in definitive hosts and do NOT replicate in the definitive host but will cause pathogenesis in the intermediate host
what are the 3 body regions of a tapeworm (cestode)
- scolex (head)
- neck
- stroblia (chain of segments)
T/F cestodes are hermaphroditic
T
Do cestodes have a digestive tract/mouth? Explain
No -> they absorb nutrients from the environment like an inside-out GI tract
what is the purpose of the scolex
embeds in the mucosa
what is the morphology of all cestode eggs? how are they laid?
hexacanth (meaning 6 hooks); laid fully larvated (infectious), usually shed in feces or shed into the environment within degenerating segments
describe the morphology of the immature stages of cestodes
great variety depending on the type of intermediate host infected and the tapeworm group
how many intermediate hosts do most cestodes have
usually only one; aquatic host tapeworms may have a second host
what are some different morphological arrangements of immature cestodes?
- cysticercus
- cysticercoid
- coenurus
- hydatid cyst
- cysticercoid
- procercoid -> plerocercoid
what are the tapeworms with mammalian IH?
Taenia, Echinococcus
what are the tapeworms with arthropodan IH
Diphylidium, Monezia, Anoplocephala
what are the tapeworms with Crustacean IH
Diphyllobothrium
what type of immature stage exists in the following types of cestodes?
Mammalian IH:
- Taenia
- Echinococcus
Arthropodan IH:
- Diphylidium
- Anoplocephela
- Monezia
Crustacean IH:
- Diphyllobothrium
Mammalian IH:
- Taenia: CYSTICERCUS, COENURUS, STROBLIOCERCUS
- Echinococcus: HYDATID CYST
Arthropodan IH: CYSTICERCOID
- Diphylidium
- Anoplocephela
- Monezia
Crustacean IH: PROCERCOID -> PLEROCERCOID
- Diphyllobothrium
what is the only tapeworm with a direct life cycle
Hymenolepsis nana
what is the general indirect life cycle of a tapeworm
eggs in feces -> hexacanth embryo infects IH -> embryo migrates to site of development and transforms into infective form (ex. cysticercus) -> IH eaten by DH -> scolex of tapeworm attaches to gut and matures
tapeworms are usually named based on their DH or IH?
IH
most tapeworms involve what type of relationship between intermediate and definitive hosts
predator-prey
For Taenia pisiformis (Rabbit Tapeworm)
- what site do adult tapeworms infect and in what species
- what site do the larvae infect and in what form and in what species
- adults in SI of dogs
- larvae are cysticercus in rabbits
what is the name of the Rabbit Tapeworm
Taenia pisiformis
Describe the morphology of the Taenia pisiformis:
- scolex
- stroblia
- segments
- egg
- scolex has 4 suckers and 2 rows of hooks
- stroblia shiny, white, tapered, and up to 2 meters
- single genital pore on each segment
- radially striated shell (embryophore), found as single eggs
what is the site of development of Taenia pisiformis in the IH and how
in the liver or peritoneal cavity; forms a cysticercus (fluid-filled bladder with an invaginated scolex)
describe the Taenia pisiformis life cycle
hexacanth eggs released from segments into the environment and are ingested by rabbits -> hexacanth larva hatches and migrates to the liver or peritoneal cavity where it forms a cysticercus -> dog eats rabbit -> scolex in the cysticercus evaginates, attaches to the gut and starts forming a stroblia
what is the PPP for Taenia pisiformis
6-8 weeks
what is the pathogenesis of Taenia pisiformis in dogs
non-pathogenic
how do we treat Taenia pisiformis in dogs
- prevent hunting to block transmission
- specific cestodicides
What is the name of the rat tapeworm
Taenia taeniaeformis
what are the IH and DH of Taenia taeniaformis
IH: rodents (especially rats and mice)
DH: felids
what is the morphology of Taenia taeniaformis
- adults
- immature
- eggs
- adults: scolex with 4 suckers and 2 hooks; stroblia up to 60cm long
- strobliocercus
- eggs are typical taeniid eggs
where does Taenia taeniaformis develop in the
- IH
- DH
IH: liver
DH: SI
what is the pathogenesis of Taenia taeniaformis in felids
no pathogenesis
how do we prevent and treat Taenia taeniaformis
- prevent hunting to block transmission
- specific cestodicides
what are the IH for Taenia crassiceps? DH?
foxes and groundhogs; dogs (zoonotic in people as well)
when would Taenia crassiceps become a zoonotic threat
immunocompromised host
what is the immature stage of Taenia crassiceps in the IH
budding cysticercus (tapioca mass)
how do we treat Taenia crassiceps
prevent hunting to block transmission; specific cestodicides
What is the name of the beef tapeworm
Taenia saginata
what is the IH and DH of Taenia saginata
IH: cattle
DH: humans
what is the immature stage of Taenia saginata in the IH and where
cysticercus in the flesh
T/F Bovine cysticercosis (Taenia saginata) is reportable
T
what are the IH and DH of Echinococcus granulosus and why do we care
IH: moose (liver)
DH: wolf/dog (SI)
ZOONOTIC
describe the morphology of Echinococcus granulosus:
- adults
- immatures
- eggs
- adults <1cm; stroblia only 3-4 segments; scolex has 4 suckers and 2 rows of hooks
- immature stages are hydatid cysts
- radially striated taeniid egg
what is the pathogenesis of Echinococcus granulosus
hydatid cysts in humans can cause a space-occupying lesion leading to pressure necrosis; rupture causes anaphylactic shock
How can you tell apart Taenia from Echinococcus eggs in dog feces
you cannot
what are the IH and DH of Echinococcus multilocularis and why do we care
IH: rodents (liver and other organs)
DH: fox (SI)
Dangerous zoonotic threat!
describe the morphology of Echinococcus multilocularis
- adults
- immatures
- eggs
adults: <1cm, only 3-4 segments in stroblia; scolex has 4 suckers and 2 rows of hooks
immatures: alveolar hydatid cyst (pieces can break off making it dangerous)
eggs: typical taeniid egg
T/F we can distinguish Taenia eggs and Echinococcus eggs
F
How do we treat zoonotic Echinococcus multilocularis and Echinococcus granulosus in humans
surgical removal and treatment with antihelmenthics
what are the DH and IH of Diphylidium caninum
DH: dogs, cats, rarely humans
IH: fleas
describe the appearance of adult Diphylidium caninum
scolex with 4 suckers and multiple rows of hooks; barrel shaped segments with pores on each side; stroblia up to 1/2m long
what is the morphology of Diphylidium immature stages and eggs
immature stages:
- cysticercoid inside the body cavity of the flea
eggs: in packets, each with an unstriated embryophore
what is the life cycle of Diphylidium caninum
eggs released into the environment -> liberated eggs ingested by flea larvae -> hexacanth embryo penetrates body cavity of insect forming cysticercoid -> adult flea ingested by dog -> scolex attaches to gut and stroblia matures
what is the PPP of Diphylidium caninum
2-3 weeks
what is the pathogenesis of Diphylidium in dogs
non-pathogenic
how can we prevent and treat Diphylidium
- specific cestodicides
- flea control
how can you tell apart Taenia segments from Diphylidium segments
have to rehydrate them to see the differences; the eggs are also different
what is the IH and DH of Anoplocephela perfoliata
DH: equids
IH: free-living mites
what is a characteristic feature of Anoplocephela
super short segments; scolex has lappets (bowtie)
what is the pathogenesis of Anoplocephela in horses
colic
what is the appearance of Anoplocephela eggs in horses
hexacanth embryo within a pyriform apparatus (molar) -> whole egg looks like a chocolate covered cherry with the pit
what are the IH and DH of Monezia sp.
IH: free-living mites on pasture
DH: ruminants
how can we tell apart Monezia eggs from Anoplocephela eggs
species! (Anoplocephela for equids vs Monezia for ruminants)
what are the IH and DH of Diphyllobothrium
IH (2): copepod (procercoid); fish (pleurocercoid)
DH: fish-eating mammals (zoonotic)
what is the morphology of Diphyllobothrium latum:
- adults
- eggs
adults: stroblia can by many m long; scolex has grooves
eggs: operculate; yellow-brown; ciliated hexacanth embryo (coracdium)
what is the pathogenesis of Diphyllobothrium latum
usually non-pathogenic but can cause pernicious anemia in predisposed humas
