HELMINTHES

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HELMINTHES

• Characteristics
• Traditionally classified in Kingdom Animalia, now
  in Domain Eucarya Super Group Opisthokonta
• Eucaryotic
• Multicellular
• Chemoorganotrophic

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• Worms may be "free living" or "parasitic
• Obligate parasites - they cannot complete their
  lifecycle without a host(s)
• Facultative - they may be parasitic but can also
  survive as free-living
• Considered as endoparasites or
• ectoparasites

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Factors in parasitology

• do not usually kill their host
• evolve elaborate cycles of reproduction
• high rate of reproduction
• complex life cycles involving 1 or more hosts -
  usually host specific
• development of specialized structures (hooks,
  suckers, etc.)
• ability to fight immune system (production of
  enzymes, changing antigens, other disguises)
• loss of structures (eyes, locomotion, etc.)

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Classification

• Phylum Platyhelminthes Flat Worms
• most primitive
• dorsoventrally flat
• nonsegmented
• acoelomic - no body cavity
• incomplete digestive tract
• free-living and parasitic
• hermaphroditic except blood flukes
• sexual and asexual reproduction
• ability to regenerate

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Class Trematoda- "Flukes"

• From lab - Fasciola hepatica, Clonorchis
  sinenesis, Schistosoma
• oral and ventral suckers which function to attach
  and aid in locomotion
• surrounded by integument whose surface contains
  spines and projections
• all flukes are parasitic as adults
• utilize snails as their first intermediate host
• produce operculated eggs which are eggs that have
  an operculum, or lid

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Operculated ova
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• Specific stages as larvae
• miracidium
• sporocyst
• redia
• cercaria
• metacercaria

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• Lifecycle of the blood flukes - Schistosoma
  japonicum, S. mansoni, S. haematobium, S.
  intercalatum, S. mekongi

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Lifecycle of liver fluke - Clonorchis sinensis
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Class Cestoda - "Tapeworms"

• From lab - Taenia, Dipylidium
• all are parasitic - endoparasites, usually in the
  digestive tract
• have an attachment organ - scolex which has hooks
  on a rostellum and suckers
• next is a neck followed by segments, or
  sections called proglottids containing
  reproductive organs which become more mature
  towards the end of the worm
• the "body" is referred to as a strobila

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• produce operculated ova like the flukes
• feed by absorbing nutrients through the body wall
• an adult cestode can range from 0.02 to 10 meters
• different species of tapeworms infect different
  hosts, many are host specific and will not infect
  other org outside the host, others will

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Lifecycle of Taenia soliumincluding
cysticercosis
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Phylum Nematoda - Unsegmented Roundworms

• From lab - Wuchereria bancrofti, Trichinella
  spiralis, Enterobius vermicularis, Ascaris
  lumbricoides, Necator americanus
• unsegmented, cylindrical, long and slender
• complete digestive system
• pseudocoelomic false body cavity - not lined
  with tissue derived from mesoderm
• separate sexes
• body is covered by a cuticle with ridges,
  striations or wart-like structures

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• Lifecycle of Enterobius vermicularis

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• Lifecycle of Ascaris lumbricoides

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Lifecycle of Necator americanus
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Lifecycle of Trichinella spiralis
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