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Parasitology 2 > 6.08 Cestodes > Flashcards

6.08 Cestodes Flashcards

1
Q

Class Cestoda common name

A

tapeworms

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2
Q

Class Cestoda: Genuses/species of importance to us

A
  • Taenia spp.*
  • Echinococcus spp.*
  • Dipylidium caninum*
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3
Q

Cestodes; Definitive vs Intermediate hosts; host specificity, replication, pathogenicity

A

Definitive Hosts
* usually highly host specific
* do not replicate in DH
* usually NOT overtly pathogenic as adults

Intermediate Hosts
* usually host specific (but exceptions)
* usually a prey species
* may be pathogenic to IH’s

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4
Q

Cestodes; Morphology - Adults

A
  • some small (a few mm in length)
  • most large (measured in meters)
  • 3 body regions
  • scolex (holdfast)
  • neck (germinal region)
  • strobila (chain of developing segments)
  • no mouth or digestive tract - absorb nutrients
  • hermaphroditic
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5
Q

Cestodes; Morphology - Eggs

A
  • hexacanth embryo fully developed within embryophore
  • eggs shed in feces or, more commonly, shed into
    environment within degenerating segments
  • morphology varies according to type of tapeworm (e.g. taenids, hymenolepids, etc.)
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6
Q

Cestodes; do all have the same immature stages?

A

great variety of forms that vary by tapeworm group and intermediate host infected

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7
Q

Cestodes; how many intermediate hosts?

A
  • most species only have a single intermediate host (the prey item)
  • some (usually tapeworms using aquatic hosts) incorporate a second IH
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8
Q

Cestodes; General Life Cycle

A
  • usually indirect (except Hymenolepsis nana)
  • eggs (free or in gravid segments) in feces
  • hexacanth embryo infects IH
  • embryo migrates to final site of development and transforms into infective form
  • transmission occurs when the IH is eaten
  • scolex of juvenile tapeworm attaches to gut and matures (begins to produce eggs)
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9
Q

Taenia pisiformis

A

Rabbit Tapeworm

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10
Q

Taenia pisiformis - Rabbit Tapeworm; General Features; what is the adult host? larval host? transfer of stages?

A
  • a typical taeniid tapeworm (example for all Taenia species)
  • adult tapeworms infect small intestine of dogs
  • the larva (a cysticercus) infects rabbits
  • predator-prey transfer of stages
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11
Q

Taenia pisiformis - Rabbit Tapeworm; Morphology - Adults

A
  • shiny white strobila, up to 2 meters long
  • scolex with 4 suckers and 2 rows of hooks on the rostellum
  • single genital pore on each rectangular segment
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12
Q

Taenia pisiformis - Rabbit Tapeworm; Morphology - Egg

A
  • typical “taeniid-type” egg, ~ 40 μm
  • has a thick radially striated embryophore
    (shell)
  • found as single eggs (not in groups like
    Dipylidium)
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13
Q

Taenia pisiformis - Rabbit Tapeworm; Morphology - Larva

A
  • a cysticercus (“Cysticercus pisiformis”)
  • fluid filled bladder containing invaginated scolex
  • “bladder worm” usually surrounded by host cyst
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14
Q

Taenia pisiformis - Rabbit Tapeworm; life cycle

A
  • a typical predator-prey life cycle
  • eggs released from segments are ingested by the IH
  • hexacanth larva hatches and migrates to the peritoneal cavity or liver to mature to a cysticercus
  • when a dog eats the rabbit, the scolex in the cysticercus evaginates, attaches to the gut and begins to form a strobila
  • PPP - 6 to 8 weeks
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15
Q

Taenia pisiformis - Rabbit Tapeworm; Pathogenesis/Lesions/Clinical Signs

A
  • non-pathogenic
  • presence of motile gravid segments in feces or perianal regions (rarely, eggs in feces)
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16
Q

Taenia pisiformis - Rabbit Tapeworm; Treatment/Prevention

A
  • specific cestodicides - praziquantel (Droncit®), nitroscanate (Lopatol®), epsiprantel (Cestex®)
  • prevent hunting to block transmission
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17
Q

Taenia taeniaeformis - Rat Tapeworm; General Features; hosts, transfer of stages

A
  • felids as definitive hosts
  • infects the small intestine
  • rodents (especially rats and mice) as IH
  • found predominantly in liver
  • predator-prey transfer of stages
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18
Q

Taenia taeniaeformis - Rat Tapeworm; Morphology - Adults

A
  • scolex with 4 suckers and 2 rows of hooks on the rostellum; strobila up to 60 cm long
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19
Q

Taenia taeniaeformis - Rat Tapeworm; Morphology - Larva

A
  • a strobilocercus (“Cysticercus fasciolaris”)
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20
Q

Taenia taeniaeformis - Rat Tapeworm; Morphology - Eggs

A
  • typical taeniid eggs
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21
Q

Taenia taeniaeformis - Rat Tapeworm; life cycle

A
  • similar in most respects to Taenia pisiformis
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22
Q

Taenia taeniaeformis - Rat Tapeworm; Pathogenesis/Lesions/Clinical Signs

A
  • non-pathogenic
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23
Q

Taenia taeniaeformis - Rat Tapeworm; Treatment/Prevention

A
  • specific cestodicides - praziquantel (Droncit®), nitroscanate (Lopatol®), epsiprantel (Cestex®)
  • prevent hunting to block transmission
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24
Q

Taenia crassiceps; General Features; hosts, how it amplifies infections, threat to humans

A
  • predator-prey cycle (foxes and groundhogs)
  • budding cysticercus amplifies infections
  • zoonotic threat if dog becomes infected (hunts)
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25
Q

Taenia crassiceps; Treatment

A
  • typical cestodicides such as praziquantel (Droncit®), nitroscanate (Lopatol®), epsiprantel (Cestex®)
  • prevent hunting to block transmission
26
Q

Taenia saginata; General Features; hosts, larva, basic adult morph, disease imortance?

A
  • predator-prey cycle (humans and cattle)
  • simple cysticercus in flesh of cattle
  • normal human parasite – unarmed rostellum
  • bovine cysticercosis is a reportable disease
27
Q

Human Taenia spp. – General Life Cycles

A
  1. Eggs or gravid proglottids in feces and passed into the environment
  2. cattle (T. saginata) and pigs (T. solium) become infected by ingesting vegetation contaminated by eggs or gravid protoglottis
  3. oncospheres hatch, penetrate intestinal wall, and circulate to musculature
    >oncospheres develop into cysticerci in muscle
  4. humans infected by ingesting raw or undercooked infected meat
  5. scolex attaches to intestine
  6. adults in small intestine
28
Q

Echinococcus granulosus; General Features; cycle, distriution/hosts, site of infection, threat to humans

A
  • typical predator-prey cycle
  • cosmopolitan distribution
  • in Canada, exists in a sylvatic moose- wolf cycle
  • adults infect the small intestine of wolf
  • immature stages found in the liver and other organs of the moose
  • NOTE: Zoonotic Threat
29
Q

Echinococcus granulosus; Morphology - Adults

A
  • smallest tapeworms of dogs, less than 1 cm long
  • scolex has 4 suckers and 2 rows of prominent hooks
  • strobila only 3 or 4 segments long
30
Q

Echinococcus granulosus; Morphology - Immatures

A
  • hydatid cyst - massive asexual replication
  • some cysts up to 50 cm in diameter
31
Q

Echinococcus granulosus; Morphology - Eggs

A
  • typical taeniid egg (radially striated) ~40 μm in diameter
32
Q

Echinococcus granulosus; Pathogenesis/Lesions/Clinical Signs

A
  • non-pathogenic to canids
  • ruminant IH’s usually unaffected
  • hydatid cysts in humans cause a space occupying lesion with pressure necrosis as they grow - rupture of the cyst can cause anaphylactic shock and rapid death
33
Q

Echinococcus granulosus; Diagnosis/Treatment - Canids

A
  • eggs in feces
    (cannot distinguish from Taenia eggs)
  • praziquantel
34
Q

Echinococcus granulosus; Diagnosis/Treatment
- Humans and other IH’s

A
  • cysts usually identified radiographically and commonly misdiagnosed as tumours
  • surgical intervention - cysts can usually be removed successfully – supplemented with anhelmintics
35
Q

Echinococcus multilocularis; cycle, distribution/hosts, site of infection, threat to humans

A
  • typical predator-prey cycle
  • cosmopolitan distribution, will infect dogs and cats
  • in Canada, exists in a sylvatic fox-rodent cycle
  • adults infect the small intestine of fox
  • immature stages found in the liver and other organs of the rodent
  • NOTE: Dangerous Zoonotic Threat
36
Q

Echinococcus multilocularis; Morphology - Adults

A
  • smallest tapeworms of dogs, less than 1 cm long
  • scolex has 4 suckers and 2 rows of prominent hooks
  • strobila only 3 or 4 segments long
37
Q

Echinococcus multilocularis; Morphology - Immatures

A
  • alveolar hydatid cyst - massive asexual replication
  • exogenous budding of cyst acts like a neoplasm
38
Q

Echinococcus multilocularis; Morphology - Eggs

A
  • typical taeniid egg, ~40 μm in diameter
39
Q

Echinococcus multilocularis; Pathogenesis – intermediate hosts including humans

A
  • Massive replication – exogenous budding and metastasis makes control difficult
40
Q

Echinococcus multilocularis; Diagnosis/Treatment - Canids

A
  • eggs in feces (cannot distinguish from Taenia eggs)
  • praziquantel Droncit
41
Q

Echinococcus multilocularis; Diagnosis/Treatment - Humans and other IH’s

A
  • cysts usually identified radiographically and commonly misdiagnosed as tumours
  • surgical removal of alveolar hydatid cyst is difficult and can be unsuccessful – can be a fatal disease
42
Q

Dipylidium caninum

A

“Double-pored tapeworm of dogs”

43
Q

Dipylidium caninum
“Double-pored tapeworm”
-hosts, site of infection

A
  • infect dogs, cats and, rarely, humans
  • uses fleas or, less commonly, biting lice as IH
    (sometimes called the “flea tapeworm”)
  • infects small intestine of DH
44
Q

Dipylidium caninum; Morphology - Adults

A
  • scolex with 4 suckers and a rostellum with several rows of fine hooks
  • strobila up to 1/2 meter long
  • segments are somewhat barrel-shaped with pores on each side
45
Q

Dipylidium caninum; Morphology - Larva

A
  • cysticercoid (about 1 mm) encysted in hemoceol
    (body cavity) of the insect IH
46
Q

Dipylidium caninum; Morphology - Eggs

A
  • eggs in “packets” (5 - 30 oncopheres in each)
  • eggs each ~40μm with a thick unstriated embryophore (membranous shell)
47
Q

Dipylidium caninum; Life Cycle

A
  • eggs usually passed within segments (motile!)
  • the liberated eggs are ingested by flea larvae
  • hexacanth embryo hatches from embryophore and penetrates into body cavity of insect
  • cysticercoid matures there (survives metamorphosis of its insect host)
  • when adult flea is ingested, scolex attaches to gut and strobila matures – PPP - 2 to 3 weeks
48
Q

Dipylidium caninum; Pathogenesis/Clinical Signs

A
  • non-pathogenic to vertebrates
  • migrating gravid segment disconcerting to animals and
    humans alike
49
Q

Dipylidium caninum; Diagnosis/Treatment/Prevention

A
  • segments in feces (rarely eggs with fecal flotation)
  • squashes of segments (+/- rehydration) for egg masses
  • cestodicides – e.g. praziquantel (e.g. Droncit®), epsiprantel (Cestex®)
  • flea control to reduce transmission
50
Q

Diagnosis of tapeworms in small animals

A
  • segments in feces (rarely eggs with fecal flotation)
  • Squashes of segments (+/- rehydration) for egg masses
51
Q

Anoplocephala perfoliata; hosts, site of infection, special morphological feature

A
  • Definitive Host - horse, ponies and other equids
  • Intermediate Host - oribatid mites (free-living mites on pasture)
  • Located at ileocecal junction
  • Scolex has “lappets”
52
Q

Anoplocephala perfoliata; Pathogenesis

A
  • suspected role in stomach upsets in horses (e.g. colic, diarrhea)
53
Q

Anoplocephala perfoliata; egg morphology, Diagnosis/Treatment

A
  • irregular eggs with pyriform apparatus
  • (pyrantel pamoate) Strongid-P or Strongid-T
54
Q

Moniezia species; hosts, site of infection, pethogenicity, treatment

A
  • Definitive Host - cattle, sheep, goats
  • Intermediate Host - oribatid mites (free-living mites on pasture)
  • located in the small intestine
  • pathogenicity of tapeworms is controversial with clinical signs only in heavily infected animals and often young animals
  • Treatment - albendazole
55
Q

Diphyllobothrium latum; what type of cestode, hosts, geographical origins

A
  • a pseudophyllidean cestode that incorporates two intermediate hosts in its life cycle
  • first IH is a copepod (procercoid)
  • second IH’s are a wide variety of fish (pleurocercoid)
  • definitive hosts are many fish-eating mammals, including humans
  • an introduced parasite (originally from Europe)
56
Q

Diphyllobothrium latum; Morphology - Adults

A
  • scolex has a pair of bothria (grooves)
  • large strobila (some many meters long)
57
Q

Diphyllobothrium latum; Morphology - Eggs

A
  • operculate, light brown egg (superficially looks like a fluke egg) with ciliated hexacanth larva
  • ciliated hexacanth embryo called a coracidium
58
Q

Diphyllobothrium latum; Pathogenesis/Lesions/Clinical Signs

A
  • usually non-pathogenic, gravid segments disturbing
  • may cause pernicious anemia (B12 deficiency) in genetically predisposed humans
59
Q

Cestodes - Tapeworms; Immature Stages - Mammalian IH

A
  • Taenia spp.
  • cysticercus (single, invaginated)
  • strobilocercus (single, invaginated, with developing strobila)
  • coenurus (multiple, invaginated)
  • Echinococcus spp.
  • hydatid cyst
  • alveolar hydatid cyst
60
Q

Cestodes - Tapeworms; Immature Stages - Arthropodan IH

A
  • Dipylidium, Monezia, Anoplocephala
  • cysticercoid
    (enclosed scolex, not inverted)

Parasitology 2 (6 decks)

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