Monogeneans and Acanthocephalans'

1
Monogeneans and Acanthocephalans.
Jo Hamilton Parasitology BS31820
1mm
0.5mm
0.5mm
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Objectives and learning outcomes.

• Describe features monogeneans acanthocephalans
  give examples.
• Recognise life cycles.
• Appreciate impact on hosts.

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Monogeneans.
1mm

• Phylum Platyhelminthes, Class Monogenea.
• Taxonomy controversial.
• Totally parasitic - typical platyhelminth
  features.
• Dorso-ventrally flattened.
• Acoelomate.
• Bilaterally symmetrical.
• Protonephridial excretory system.
• No definite anus.
• No respiratory / circulatory system.
• Usually hermaphrodite.

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Monogeneans.

• Ectoparasites.
• Gills / body surface marine freshwater fish.
• Amphibians reptiles.
• One species - mammals, Oculotrema hippopotami
  hippo eye.
• Mesoparasites? may invade buccal cavity, cloaca
  bladder.

1mm
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Monogeneans.
1mm

• Large posterior sucker haptor.
• Hooks.
• 10 - 14 marginal.
• Pair large median hooks
• hamuli.
• Haptor adaptations -
• sucker-like organs.
• Suckers - sclerites - clamp gill
  filaments.

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Monogeneans Body plan - Tegument.

• Syncitial surface layer.
• Cell bodies sunken in parenchyma.
• Cytoplasmic bridges.
• Microvilli.
• Musculature - outer circular, oblique inner
  longitudinal muscle fibres.

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Monogeneans Digestive system.

• Mouth, pharynx bifurcate intestine - no anus.
• Intestine - intercaecal network.
• Nutrients also via tegument - physiological
  significance?
• Specific microhabitats on host
• Little movement.
• Adults not transferred host-to-host.
• Skin some gill dwellers - mucus feeders.
• Most gill dwellers - blood feeders (brachial
  capillaries).

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Monogeneans Reproductive system.

• Hermaphrodite.
• Vitellaria, ovary, ootype Mehlis' gland
  uterus.
• Single testis, seminal vesicle muscular penis.
• Monogeneans often have pair vaginas.
• May have genito-intestinal canal.

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Monogeneans Life cycle.

• Direct development.
• Monogenea 1 generation. 1 egg 1 adult

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Monogeneans Life cycle.

• Eggs - water - hatch.
• Eggs large.
• Long filaments - extensions egg envelope.
• Filaments stick eggs to skin of fish.
• Or eggs form mass - fish respiratory currents.

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Monogeneans Life cycle.

• Hatched egg oncomiracidium.
• Ciliated larva swims - eyespots haptor.
• Complex anterior eyes orientation host
  location.
• Rhabdomeric photoreceptors.
• Oncomiracidial digestive tract well
  differentiated.
• Excretory pores formed.
• Haptor - attachment.
• Loose ciliated coat.
• Growth to adult stage more complex haptor.
  

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Monogeneans Host location.

• Evolved host location mechanisms.
• Eggs produced when fish shoaling.
• Oncomiracidia hatch during daytime.
• Respond chemical physical stimuli (e.g. mucus
  respiratory currents - gills).
• Can locate hosts over short distances.

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Example 1 Polystoma intergerrimum.

• Rare - endoparasitic.
• Adult - bladder of Old World frogs.
• Repro cycle synchronized with that of host.
• Worms 4 to 5 years - mature.
• Dormant until frog enters repro cycle.
• Gonadotrophins in frog induce parasite
  copulatation oviposition.
• Eggs - frog's urine.
• 20 -50 days to hatch - oncomiracidia.
• Meanwhile frogs spawned tadpoles hatched.

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Monogeneans Polystoma intergerrimum.

• Tadpoles 2 phases - External gills internal
  gills.
• Oncomiracidium attaches external gills -
  neotenic larva.
• Produces eggs - 20-25 days.
• Morphologically physiologically different from
  adult.
• Neotenic larva gills. Adult bladder.
• Eggs hatch - 15 -20 days larvae attach to
  tadpole gills.

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Monogeneans Polystoma intergerrimum.

• No development until tadpoles metamorphose.
• Resorption of gills - worms migrate over surface
  to bladder via urinary tract.
• Takes 1 minute.
• Endogenously programmed.

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Monogeneans Polystoma nearcticum.

• P. nearcticum - North American tree frogs.
• Neotenic form - larvae do develop or migrate
  unlike P. intergerrimum.
• Enter urogenital tract directly.

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Example 2 Diplozoon paradoxum.

• Diplozoon paradoxum - freshwater fish.
• Adult body 2 individuals fused together.
• Larva diporpa.
• No development unless 2 diporpa larvae.
• Ventral sucker grasps dorsal button.
• Triggers metamorphosis 2 larvae fused.
• Intestine through both individuals.
• Male female reproductive ducts fused.

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Monogeneans Gyrodactylus.

• Gyrodactylus sp. - freshwater marine fish).
• No larvae.
• Adults viviparous.
• Polyembryony.
• Each zygote - 4 groups cells.
• Each separate larva.
• Larvae enclosed inside
• each other - Russian dolls.

0.8mm
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Monogeneans Gyrodactylus.

• Adult 0.5 to 0.8 mm long.
• Haptor - 16 marginal hooks 2 hamuli.
• Important in fish farms.
• Increased host contact increase parasite
  population.
• Wide range hosts guppies trout.

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Monogeneans Gyrodactylus.

• Parasite repro cycle crucial.
• Entire repro cycle on host.
• Larvae - uterus adult worm.
• Polyembryony - 4 individuals from single zygote.
• Rapid increase in parasite numbers.
• Parasites spread between fish in close contact.
• Worms can survive short periods off host.

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Acanthocephalans (Spiny/ thorny-headed worms).

• Name - Greek Acantha prickle Kephale head.
• Not commonly encountered.
• Hosts fish, amphibians, birds, mammals. 
• Characteristic anterior, protrusible proboscis
  - hooks. 
• Hence common name.

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Acanthocephalans history of taxonomy.

• Recognised beginning 18th century.
• Koelreuther (1771) - Acanthocephala .
• Muller (1776) - Echinorhynchus.
• Rudolphi (1809) - Acanthocephala.
• Many species described 19th century
  -Echinorhynchus.
• Position uncertain Aschelminthes?
• Acanthocephala now separate phylum.

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Acanthocephalans.

• Interesting important group.
• Endoparasites.
• No gut.
• Few mm long largest recorded1m?
• Adult acanthocephalans intestinal parasites of
  vertebrates (fish, rodents birds).
• Arthropods intermediate hosts (1 mollusc).

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Acanthocephalans.

• Adult characteristics
• Spiny retractable proboscis - attachment.
• No gut.
• Pseudocoelomate.
• A pair of lemnisci.
• Dioecious.

0.5mm
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Acanthocephalans Adult morphology.
0.5mm

• Anterior presoma (proboscis, neck).
• Main trunk metasoma.
• Cutuicular partition.
• Proboscis sheath.
• Longitudinal circular muscles.
• 2 hydrostatic systems - main body cavity
  proboscis sheath cavity.

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Acanthocephalans Adult morphology.
0.5mm

• Eversion probocis
• hydrostatic.
• Proboscis movement
• lemnisci.

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Acanthocephalans Body plan.

• Body wall structure.
• Absorb nutrients through body wall.
• 5 major layers
• epicuticle, cuticle, striped layer, felt layer
  radial layer.
• Pore canals.
• In radial layer - lacunar canal system.
• Lacunar canal system - liquid lipid
  hydrostatic?.

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Acanthocephalans Body plan.

• Eutely - members same species same number cells
  in organs.
• Nuclei in body wall used in taxonomy.
• Polyploidy also common in nuclei up to 343n (n
  haploid)!

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Acanthocephalans Excretory system.

• Absent - some flame cells (protonephridia).

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Acanthocephalans Reproductive system.

• Dioecious.
• Unique repro organs.
• Male - paired testes, sperm duct, penis
  copulatory bursa.
• Unicellular cement glands copulation sealing.
• Female -ovaries (initially in ligament sac)
  ovarian balls in adult.

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Acanthocephalans Reproductive system.
0.5mm

• Eggs fertilised in ovarian
• ball.
• Complete development
• in pseudocoelom.
• Mature eggs
• uterine bell.
• Eggs sorted.
• Immature eggs
• pseudocoelom.
• Mature eggs - uterus
• vagina.

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Acanthocephalans Life cycle.

• Life cycle - 25 species.
• Same basic pattern.
• Adults in intestine definitive host. 
• Dioecious.
• Females - eggs - faeces. 
• Eggs ingested by an arthropod intermediate
  host.
• Definitive host infected - eats intermediate host
  - cystacanth.

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Acanthocephalans Life cycle.

• Intermediate host - arthropod.
• 1 exception - mollusc.
• May involve paratenic hosts.
• No human infections.
• Major problems fish farms.
• Difficult to treat.

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Acanthocephalans Impact on host.

• Infection intensity high
• E.g. 1000 in duck intestine.
• Reproductive capacity high
• 10,000,000 eggs per female.
• Much damage - hooks.

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Acanthocephalans Impact on host.

• Polymorphus botulus - no damage intermediate
  crab host.
• Eider duck (Somateria mollissima) - definitive
  host.
• 100-750 P. botulus in intestine.
• Seasonal "outbreaks" of disease mortality.

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Acanthocephalans Impact on host.

• Economic importance?
• P. botulus - sea ducks crabs.
• But infections in commercial lobsters (Canada).
• Acquired from crabs?
• Lobster diet.
• Cystacanths in lobsters econmic loss.
• No prevention / control.

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Summary I.

• Monogenea
• Direct life cycle.
• Mainly ectoparasites.
• Endoparasite Polystoma intergerrimum. repro
  parasite linked to repro host.
• Haptor hooks.
• Hamuli.
• Economic importance Gyrodactylus sp.

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Summary II.

• Acanthocephala
• Indirect life cycle.
• Spiny anterior proboscis.
• Unique repro organs.
• Uterine bell.
• Economic importance - Polymorphus botulus.
• No effective prevention / control.
• -