introduction to the helminth parasites
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Introduction to the helminth parasites
BVM&S ParasitologyTudor W Jones
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Taxonomic Relationships of the Helminth Parasites
Trematodes"Flukes"
Cestodes"Tapeworms"
Platyhelminthes"Flatworms"
Roundworms
Lungworms
Hookworms
Pinworms
Nematodes
Nemathelminthes"Roundworms"
Acanthocephala"Spiny-headed worms"
ParasiticHelminths
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Why are helminths important ?
• Production losses due to– Competition for nutrients– Damage to body systems e.g. gut, liver– Death
• Animal welfare– Companion animals – Food animals
• Public health (zoonotic infections)
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Where do helminths live?BRAIN
Tapeworm larvae
LUNGSLungworm
Tapeworm larvae
BLOODFlukesFilarial worms
ABOMASUMNematodes
LIVERFluke
Tapeworm larvae
SMALL INTEST.Nematodes
Adult tapeworms
LARGE INTEST.Nematodes
MUSCLETapeworm larvae Skin
Filarial worms
In the environment
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Lecture topics
• Diagnosis & disease– Morphology– Feeding– Reproduction– Behaviour in the host
• Epidemiology & control– Life cycles– Survival strategies
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Morphology• External features
– Size– Shape– Functional anatomy
• Internal features– Outer layer– Structural– Functional
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Same parasite - different appearance
• Adults– Males– Females
• Eggs• Juvenile
– Cysts– Larvae
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Feeding
• Passive feeders• Browsers• Tissue feeders
– Solid tissues– Blood
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Reproduction
• Asexual– Multiplication– Parthenogenesis
• Sexual– Monoecius– Dioecius
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Behaviour in the host
• Non-migratory • Migratory
– Hepato-tracheal– Somatic
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Life cycles
• Direct• Indirect
– Definitive Host– Intermediate host– Arthropod (vector)
borne
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Example of a simple, direct life cycle
Adults
Egg
L1
L2L3
L4
L5
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Example of a complex, indirect life cycle
Eggs pass out in faeces
Larval stage develops inside
egg
1st
intermediate host ingests
egg
Larval stage passed out in
slime ball
2nd intermediate host ingests slime ball
Definitive host ingests ant
while grazing
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Host types• Definitive host
– Host where adult stages develop
• Intermediate host– Host where immature stages develop, indirect life cycle only
• Transport host– Immature stage not retained, no parasite development
• Paratenic host– Immature stage retained but no parasite development
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Survival strategies
• Permanent parasites• Temporary parasites
– Morphological adaptations
– Physiological adaptations
• Hypobiosis• Critical hatching
conditions• Peripatruriant rise
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Ascarid egg
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Hypobiosis
• Physiological - Toxocara Larvae enter hypobiotic state in tissuesLarvae reactivated during pregnancy in dogs &
cats and infect foetus• Seasonal - Ostertagia
– Larvae taken in during Autumn overwinter in the gastric glands of the abomasum
– Larval development resumes in Spring giving rise to new generation of adults
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Critical Hatching Conditions
• Larvae overwinter on the pasture inside the egg stage.
• Larvae hatch onto pasture only after receiving an environmental trigger
• Trigger is usually a change in temperature.
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Periparturient (Spring)Rise
• Increase in parasite egg counts around parturition time – usually spring in UK
• Impact – large numbers of infective larvae on the pasture when– Pasture conditions optimum for survival– Young animals available for infection
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Trichinella
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Characteristics of helminths
Worm-likeTape-likeLeaf-likeAppearance
DioeciousMonoeciousMonoeciousReproduction
Direct & indirectIndirectIndirectLife cycle
True gutAbsentBlind sackGut
Fluid-filledAbsentAbsentBody cavity
CylindricalFlattenedFlattenedCross-section
NematodeCestodeTrematode
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Internal structure - Nematodes
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Internal structure - Trematodes
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Internal structure - Cestodes
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Adult stages of the helminths (not to scale)
Trematodes Cestodes
Nematodes
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Feeding adaptationsBrowsing
Tissue feeding
Blood feeding
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Males & FemalesBursa
Vulval flap
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Helminth Body Structure (TS)
NematodeUterus with eggs Gut
Trematode
Nerve chord
Testes
Uterus with eggsSolid
parenchyma
Cestode
Solid parenchyma
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Two forms of migration
Gut
LiverLung
In Out Gut
Somatictissues
In Out
Hepato-trachealmigration Somatic migration