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Parasitology 1 > 6.7 Introduction to Helminths and Trematodes > Flashcards

6.7 Introduction to Helminths and Trematodes Flashcards

1
Q

Helminth:

A

WORM; esp. an intestinal worm ‐ used esp. by parasitologists

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2
Q

Helminths; phyla

A
  • Phylum Nematoda: the roundworms
  • Phylum Platyhelminthes:
    Class Monogenea
    Class Cestoda ‐ tapeworms
    Class Trematoda ‐ flukes
  • Phylum Annelida: Leeches, earthworms, etc.
  • Phylum Acanthocephala: Thorny‐headed worms
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3
Q

Flatworms are what phylum?

A

Phylum Platyhelminthes

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4
Q

Phylum Platyhelminthes; Classes

A

Flatworms

  • Class Monogenea
  • Class Trematoda (trematodes)
    ‐ Aspidogastrea
    ‐ Digenea
  • Class Cestoda (tapeworms)
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5
Q

Flukes are what? Phylum, classes, common hosts:

A

Phylum Platyhelminthes

Class Monogenea (“Anchor worms”):
* generally ectoparasites (often gills of fish) of fish, amphibians or reptiles

Class Trematoda:
* Order Aspidogastrea
‐ common parasites of molluscs, reptiles and amphibians (aquatic hosts)
* Order Digenea
‐ definitive hosts often mammals (most important from veterinary perspective)

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6
Q

orders of class trematoda and features hosts:

A

Class Trematoda:
* Order Aspidogastrea
‐ common parasites of molluscs, reptiles and amphibians (aquatic hosts)
* Order Digenea
‐ definitive hosts often mammals (most important from veterinary perspective)

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7
Q

Flukes ‐ General Morphology; Adults ‐ Digeans

A
  • often dorso‐ventrally flattened
  • spiny cuticle often observed
  • two suckers (ventral and oral)
  • esophagus and blind ceca for food
  • hermaphroditic in many, but not all, species
  • female ‐ ovary, prominent uterus, vitellaria
  • male ‐ paired testes
  • sex organs share a common genital pore
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8
Q

Flukes; Immature Stages ‐ Digeans
What are the life stages? Where are they found?

A
  • miracidium > sporocyst > redia > cercaria (optionally > meta/mesocercaria)
  • most stages are found within the intermediate host(s) but some may also be free in the environment or attached to vegetation
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9
Q

Flukes ‐ General Morphology; Eggs ‐ Digeans

A
  • oval or egg‐shaped
  • operculate ‐ has a “hatch” from
    which the miracidium emerges
  • usually yellow to golden brown smooth shell
  • contents of egg usually completely fill the egg
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10
Q

features typical of all fluke/trematode eggs

A
  • operculate ‐ has a “hatch” from which the miracidium emerges
  • usually yellow to golden brown smooth shell
  • contents of egg usually completely fill the egg
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11
Q

Digeans ‐ General Life Cycle, hosts

A
  • digeans have an indirect life cycle
  • snails/slugs are always the first intermediate host
  • digenetic flukes are normally highly host‐specific for their intermediate mollusc host
  • somewhat less specific in their choice of definitive vertebrate host
  • geographic distribution of parasite
    usually follows that of its intermediate snail host
  • miracidium leaves egg through operculum
  • miracidium penetrates snail tissues
    (host‐specific event)
  • asexual replication (sporocyst and redia) give rise to a large number of cercariae
  • cercariae then do one of the following:
    > penetrate the definitive host (form adults)
    > encyst on vegetation or in an intermediate host (forming metacercaria)
    > penetrate intermediate host (forming mesocercaria)
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12
Q

Alaria spp.; Hosts affected

A
  • cats or dogs act as definitive hosts
  • snails and tadpoles act as intermediate hosts
  • numerous possible paratenic hosts (including humans ‐ zoonotic threat)
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13
Q

Alaria spp.; Morphology ‐ Adults

A
  • small fluke about 1 cm long
  • body has two regions (anterior flattened part and cylindrical posterior region)
  • anterior region has the oral and ventral suckers
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14
Q

Alaria spp.; Morphology ‐ Eggs

A
  • 130 μm or less, yellow brown, operculate
  • segmented embryo in fresh feces
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15
Q

Alaria spp.; Life Cycle

A
  • indirect life cycle (like all digenetic trematodes)
  • immature eggs passed in feces (uninfective)
  • miracidium matures and eggs hatch in water
  • miracidium penetrate snails
  • cercariae penetrate tadpoles and become mesocercariae (unique to Alaria ‐‐ this form is a potential zoonotic threat to humans, usually through ingesting undercooked paratenic hosts)
  • fluke completes development when the intermediate or paratenic host ingested by DH
  • mesocercariae migrate to lungs and become metacercariae
  • metacercariae mature, migrate up respiratory tract and are swallowed
  • adult flukes mature in small intestine
  • PPP‐5weeks
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16
Q

Alaria spp.; Pathogenesis

A
  • adult flukes found attached to small intestine, usually in tightly packed clusters
  • not normally pathogenic except in massive infections
  • parasites do not replicate in definitive host or paratenic hosts (only in snails)
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17
Q

Alaria spp.; Diagnosis

A
  • typical eggs on fecal flotation
18
Q

Nanophyetus salmincola

A

“Salmon Poisoning Fluke”

19
Q

Nanophyetus salmincola; General; range, significance

A
  • restricted to the Pacific Northwest and Siberia * not of clinical significance on its own
  • acts as a vector for Neorickettsia helminthoeca
20
Q

Nanophyetus salmincola; hosts

A
  • DH ‐ dogs, cats and mink
  • IH ‐ snail and then fish
21
Q

Nanophyetus salmincola; Morphology ‐ Adults

A
  • small (2 mm or less), creamy white
22
Q

Nanophyetus salmincola; Morphology ‐ Eggs

A
  • small (up to 80 μm)
  • indistinct operculum
  • yellowish brown shell
23
Q

Nanophyetus salmincola; Life Cycle

A
  • typical digenetic life cycle
  • eggs passed in feces hatch in water
  • miracidia penetrate snails
  • cercariae produced in snails penetrate fish and encyst (metacercariae)
  • DH ingests IH to release fluke which then moves to small intestine
  • PPP about 1 week
24
Q

Nanophyetus salmincola; Pathogenesis

A
  • normally none from the flukes
  • Neorickettsia helminthoeca causes a sudden febrile illness with fever, vomiting, diarrhea, weight loss, lymphadenopathy
  • rickettsial disease causes high mortality
25
Q

Nanophyetus salmincola; Treatment

A
  • rickettsia can be treated with tetracyclines
26
Q

Paragonimus sp.

A

“Lung Flukes”

27
Q

Paragonimus sp.; Morphology ‐ Adults

A
  • ovoid, relatively large flukes (up to 16 mm)
  • found within cysts in pairs ‐ reddish‐ brown from the eggs within uteri.
  • spiny cuticle
28
Q

Paragonimus sp.; Morphology ‐ Eggs

A
  • small (up to 80 μm) with distinct operculum (look like shoulders around the “hatch”
  • yellowish brown shell
29
Q

Paragonimus sp.; Life Cycle, PPP

A
  • typical digenetic life cycle
  • eggs laid in cysts are shed into bronchioles where they are swept up the respiratory tract to be swallowed
    ‐ eggs found in feces
  • miracidia penetrate snails
  • cercariae penetrate crayfish and encyst (metacercariae)
  • DH ingests IH to release fluke which then excysts in the small intestine
  • flukes migrate to lung and associate in pairs in lung parenchyma near bronchioles
  • fibrotic cyst forms around the paired flukes
  • PPP:
    > dogs,4‐5weeks
    > cats, up to 10 weeks
30
Q

Paragonimus sp.; Pathogenesis/Clinical signs

A
  • fibrotic cyst forms around paired worms with associated bronchiolitis
  • golf ball‐sized cysts found in right caudal lobe
  • atelectasis and adhesions may surround cysts
  • often asymptomatic, may cause coughing
  • may induce dyspnea and lethargy in more pronounced cases
31
Q

Paragonimus sp.; Diagnosis

A
  • clinical signs and history (access to water)
  • typical eggs can be found on fecal flotation
32
Q

Paragonimus sp.; Treatment

A

(all off‐label usage)
* Albendazole (Valbazen®)
* Fenbendazole (Panacur®)

33
Q

Fasciola hepatica

A

“Liver Flukes”

34
Q

Fasciola hepatica; General; Where found in Canada, hosts, zoonosis, eggs, diagnosis

A
  • infrequently observed parasites of ruminants in Canada, usually imported animals
  • severely restricted geographically
  • large leaf‐like adults in bile ducts of sheep, zoonotic threat
    – “cephalic cone”
  • eggs with indistinct operculum
  • often only diagnosed post‐mortem
35
Q

Liver Flukes – Life Cycles

A

Unembryonated eggs passed in feces
 Eggs in feces hatch in water
 Miracidium penetrates snail
>in snail tissue: sporocysts > rediae > cercariae
 Cercaria liberated from the snail and encysts on vegetation as a metacercaria
 When a sheep ingests the metacercaria with herbage, the juvenile fluke is liberated and migrates through the intestine, the peritoneal cavity and liver capsule. In the liver, the fluke migrates for a period through the parenchyma before attaining the bile duct to mature as an adult
 PPP = 10-12 weeks

36
Q

Fasciola hepatica; Pathogenesis

A
  • located within bile ducts where an extensive fibrosis of the duct wall occurs
  • so‐called “pipe stem” fibrosis of the liver
  • may progress to carcinoma of the liver
37
Q

Fascioloides magna

A

“American Liver Fluke”

38
Q

Fascioloides magna; Hosts, where found, site of infection, diagnosis

A
  • frequently seen in wild cervids in Canada
  • widely distributed geographically
  • large leaf‐like adults in cysts within liver with ducts leading to bile ducts
  • often only diagnosed post‐mortem
39
Q

Fasciola hepatica vs Fascioloides magna differentiating physical feature

A

Fasciola hepatica - Adult - cephalic cone
Fascioloides magna - Adult – no cephalic cone

40
Q

Fascioloides magna; Pathogenesis – Wild and Domestic Cervids

A
  • NO clinical signs
  • patent infections – typical fluke eggs on fecal float
41
Q

Fascioloides magna; Pathogenesis ‐ Cattle

A
  • normally NO clinical signs
  • DO NOT become patent
42
Q

Fascioloides magna; Pathogenesis ‐ Sheep

A
  • mortality is evidence of infection
  • flukes migrate constantly and destroy liver through these migrations
  • patent infections usually DO NOT develop – mortality first

Parasitology 1 (8 decks)

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