III   Phylum Platyhelminthes

 

  1. Introduction:

    1. Classes

      1. Trematoda-  flukes

      2. Cestoda-  tapeworms

    2. Characteristics-

      1. Flat body with a hold fast organ and suckers

      2. Indirect life cycle with one or more intermediate hosts

      3. Nutirition-  either acoelomate (cestodes) or with a simple blind gut (flukes)

  2. Class Trematoda (Subclass Digenea)

    1.  General information-

      1. Type of parasite-  obligate temporary endoparasite

      2. Body type-  leaf-like

      3. Host specificty-

        • Adult-  fairly low to moderate

        • Immature-  very high

      4. Life cycle-

        • Indirect  (one or more intermediate hosts)

        • First intermediate host is always a snail

        • Adult-  Species-specific site 

        • Egg 
          Operculated with thin shell                                
          Approx. 500 um  
          In water

        • Miracidium
          First larva
          Free living in water

        • Sporocyst
          Second larva
          In snail IH

        • Redia
          Third larva 
           In snail

        • Cercaria 
          4th larva
          Free living in water

        • Metacercaria
          Encysted in second IH or on plants                                  
                                                                                   

      5. Pathology-

        • Competition for nutrients

        • Direct damage (ex. destruction of liver)

        • Vector for pathogens (esp. Clostridium novyi bacteria)

      6. Diagnosis-  sedimentation (eggs very large & heavy-  will not float in media)

    2. Some important examples:

      Species Common name Host Foreyt
      Alaria Intestinal fluke Carnivores 30-31
      Dicrocelium
      dendriticum      		 Lancet fluke Ruminants -
      Fasciola hepatica Common liver fluke Ruminants & man 90- 91
      Heterobilharzia Canine schistosome Dogs -
      Nanophyetus salmincola Salmon-poisoning fluke Canines 30 - 31
      Paragonimus kellicotti Lung fluke Dog, cat, pig... 30-31, 56-57
      Paramphistomum Rumen fluke Ruminants 95
      Trichobilharzia Swimmer's itch (in people) waterfowl, man 155

       

  3. Class Cestoda:

    1. General information-

      1. Type of parasite-  obligate temporary endoparasite

      2. Morphology-

        • Adult-

          • Basic form-  long flat body (maximizes surface area for food absorption)

          • Scolex-  specialized holdfast device (may have projecting rostellum at cranial end)

          • Proglottid-  independent reproductive unit that matures progressively

          • Strobila-  linear set of proglottids

        • Ova-

          • Oval to pear-shaped embryo with 3 pairs of hooklets

          • Usually has thick striated wall

      3. Life cycle-

        • Indirect (except for Hymenolepis nana)

        • Final host-  vertebrate-  located in small intestine

        • Intermediate host-  larvae encysted somewhere in host's body

        • Length varies with the species

      4. Larvae-

        • Located in the intermediate host

        • Cysts-

          • Fully developed scolex or scolices in sac

          • Surrounded by connective tissue capsule from host (usually)

        • Types-

          • Cysticercus-  one scolex in fluid-filled sac  (in mammals)

          • Cysticercoid-  one scolex in solid sac (in arthropods)

          • Coenurus-  many scolices in a fluid-filled sac

          • Hydatid cyst-  many scolices in multiple sacs 

      5. Importance

        • Adults-  usually nonpathogenic (except in horse)

        • Larvae-  may cause severe problems, esp. when man acts as an intermediate host  (larvae end up in lungs, liver & brain)

    2. Some important species
      Species Common Name Host Foreyt
      Anoplocephala Equine tapeworm Horse (mite) 130-131
      Diphyllobothrium latum Broad fish tapeworm Dog & man (fish) 37
      Dipylidium caninum Flea tapeworm Dog & cat (flea) 32-33, 58-59
      Echinococcus granulosus Hydatid tapeworm Dog (rodents & man) 32-33, 96
      Echinococcus multilocularis Alveolar hydatid tapeworm Carnivores (rodents & man) -
      Moniezia Ruminant tapeworm Ruminent (mite) 90-91
      Taenia multiceps Gid tapeworm Sheep (dogs) 36, 97
      Taenia pisiformis Canine tapeworm Dog (rabbit) 32-33
      Taenia saginata Beef tapeworm Man (cow) 95
      Taenia solium Pork tapeworm Man (pig, man) 148
      Taenia taeniaformis Feline tapeworm Cat (rodent) 58-59

       

    3. Dipylidium caninum

      1. Common name:   flea or double-pored tapeworm

      2. Hosts:

        • Final-  dogs & cats (small intestine)

        • Intermediate -  flea & dog louse 

        • Zoonotic-  possible

      3. Appearance:

        • Adult-

        • Ova-

          • Packets of 5 - 30 eggs

          • Packet is oval & eggs are round

          • Individual eggs are approx. 40 um in diameter

          • Packet up to approx. 200-300 um long

          • Eggs are not released from the proglottid until the proglottid exits the host (i.e. ova will not be found distributed throughout the feces, but may be found on the fecal surface)

        • Larvae-  cysticercoids

      4. Prepatent period:  2 - 3 weeks

      5. Life cycle

      6. Pathology in final host: 

        • Fairly low

        • Rarely causes enteritis

        • Primarily an anesthetic  & public health issue

      7. Control-  MUST CONTROL THE INTERMEDIATE HOST!!!

    4. Taenia pisiformis and Taenia taeniaformis

      1. Common names:  

        • Taenia pisiformis-  canine or dog tapeworm

        • Taenia taeniaformis-  feline or cat tapeworm

      2. Hosts-

        • Zoonotic-  no

        • Intermediate and final hosts-

          Parasite Intermediate Host Final Host
          Taenia pisiformis Rabbit viscera Dog small intestine
          Taenia taeniaformis Rodent viscera Cat small intestine

           

      3. Appearance-

        • Adults-

          • Proglottids are rectangular with unilateral genital pores

          • Adult size to 200 cm long

        • Ova-

          • Single

          • Round

          • 30 - 40 um diameter

          • Exit proglottid both before and after feces exit host (i.e. eggs may be mixed throughout fecal sample)

        • Larvae-  cysticerci on liver and other viscera

      4. Life cycle

      5. Prepatent period-  8 weeks 

      6. Pathology in final host-  rarely pathogenic

      7. Control-  MUST CONTROL HUNTING BY DOGS & CATS!!!

    5. Echinococcus granulosus

      1. Common name-  hydatid tapeworm

      2. Hosts-

        • Final-  canids (small intestine)

        • Intermediate-  sheep and others (including man)

        • Zoonotic-  yes

      3. Appearance-

        • Adults-

          • Only 3 - 5 proglottids per strobila

          • Maximum size 5 mm

        • Ova-  identical to Taenia ova

        • Larvae-  hydatid cysts, esp. in liver and lungs

      4. Life cycle

      5. Importance-

        • Enzootic in intensive sheep farming areas

        • Generally nonpathogenic in final host

        • In intermediate host-  may cause pain, hepatomegaly, cough...

    6. Echinococcus multilocularis

      1. Common name:  alveolar hydatid tapeworm

      2. Hosts-

        • Final-  canids (esp. fox & coyotes) and cat

        • Intermediate-  voles, lemmings and others

        • Zoonotic-  yes

      3. Appearance-

      4. Life cycle

      5. Importance-

        • Alveolar hydatid disease

        • "Most lethal zoonotic helminth"

        • Hydatid cyst with little or no host response results in invasive cysts (metastasize)

        • Spreading from far north as far as Ohio

    7. Moniezia and Anoplocephala spp.

      1. Common names-

      2. Hosts-

        • Ruminants and horses

        • Intermediate host-  oribatid grain mite  (nonparasitic)

        • Zoonotic-  no

      3. Ova-  

        • Square to triangular with pyriform (pear-shaped) embryo. 

        • 50 - 75 um diameter

      4. Importance-

        • Ruminants-  minor

        • Horse-  may cause worry, poor weight gain or difficulty maintaining weight,  intermittent colic, diarrhea...

    8. Hymenolepis nana  (Vampirolepis nana)

      1. Common name-  dwarf tapeworm

      2. Hosts-

        • Final-  rodents and man

        • Intermediate-

          • NOT NEEDED  (ova directly infective)

          • Can use flour beetles and other insects

      3. Ova-  similar to Taenia

      4. Pathology-  usually low, but may cause enteritis & anorexia

03/17/03

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