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					   Cestode parasites
Medical Parasitology, CBIO4500
      January 28, 2010

         Professor Marshall Lightowlers, Principal
         Research Fellow, Faculty of Veterinary
         Science. He has been striving towards the
         parasite’s eradication for almost 30 years.
                        Turbellarians   worms

Phylum Platyhelminths
                        Monogenea       flukes

                        Trematodes       flukes

                        Cestodes        Tapeworms
Phylum Nematoda
           Review Schistosomes
 They live in the bloodstream
 They live for a long time
 The host can become
 resistant to infection
 The parasites do not
 replicate in their definitive host
 Pathology is not due to host
 response against the worms but rather to
 eggs entrapped in tissues
 Infect 200 millions of the world‟s
 population in Africa, Asia and S. America.
 Population at risk: 600 millions
 Disease: schistosomiasis or Bilharzia
 They need a snail IH for transmission
            Tapeworms: the Cestodes
• They are flat in cross
• Hermaprhoditic
• Live in the intestines
  with feces
• Life cycles are complex
  and can include multiple
  intermediate hosts
• No mouth, no
  digestive system
• They have suckers and
  teeth that grasp the host.
• Reproductive structures       http://www.ndpteachers.org/perit/biology_image_gallery1.htm

• Behind a short neck are
  repeated parts of the worm, each containing reproductive structures with
  eggs and sperm, which can be released with the host's feces.
• The pieces give the worm a ribbon-like structure, beneficial for absorbing
  nutrients from the intestine.
• Order pseudophyllidea: have scolex with bothria; the sperm whale tapeworm, H.
physesteris, can be > 30 m long; the genital pore and uterine pore are located on the mid-
ventral surface, and the ovary is bilobed ("dumbbell-shaped"); each segment has 4-14
complete sets of genitalia, can be up to 45,000 segments in a worm
          • Diphyllobothrium sp.

           Diphyllobotrium latum
• Order cyclophyllidea: most important group of tapeworms of humans and
domestic animals, multiple proglottid, scolex ("head") with four suckers. Proglottids have
genital openings on one side (except the family Dilepididae, which has them on both sides),
and a compact yolk gland or vitellarium posterior to the ovary; can be small (a few mm's) or
large (up to 10 m); mammals serve as intermediate hosts
          • Family Taeniidae:Taenia saginata, Taenia solium, taenia multiceps;
          Echinococcus granulosus, E. multilocularis
          • Family Hymenolepididae: Hymenolepis diminuta, Hymenolepis nana,
The tapeworm life cycle involves a definitive host and one or
more intermediate hosts (IH).
Exception: Hymenolepis nana only uses one
host and D. latum has 2 IHs
• INTERMEDIATE: ingests the eggs
which develop into larval forms and
later into encysted forms in
extraintestinal tissues. Each parasite
species has specialized larval forms.
• DEFINITIVE: Harbors the mature
forms of the parasite. Carnivorous or
omnivorous mammal that acquires
infection by consuming larval cysts in
the uncooked tissues of an IH
           • The body plan of adult
scolex     cestodes includes a scolex
           (looks like the “head”), a
neck       neck and strobila that can
           extend for only a few
           proglottids or thousands
           • The strobila is not truly
           metameric though as
           several organs like the
           excretory system extend
           through the entire worm
           • Proglottid: each individual
           • Most worms are very long:
           occupying the entire length
           of small intestine
                                               Morphology of tapeworms:
                                                      The scolex
                                               The scolex is the part of the
                                               worm that anchors it to the
                                               intestinal epithelium and
                                               prevents that the worm is
Scolex of Taenia Solium.                       passed with the digested food

                                               The scolex structure varies
?products_id=813                                                                    Scolex of Diphyllobothrium latum.

                                               between species of tapeworms.
                                               a. Diphyllobothrium latum has
                                               a scolex with elongated, slit-like
                                               attachment organs (bothria)
                                               b. Taenia saginata has four
                                               muscular SUCKERS.
                                               c. Taenia solium has similar
                                               muscular SUCKERS and a
                                               ROSTELLUM with rows of
                                               chitinous hooks.                     Scolex of Taenia Saginata
• In most cestodes the scolex is tiny when
  compared to the strobila which makes up
  most of the actual “worm”
• The strobila consists of a linear series of
• Tape worms are hermaphrodites and each
  proglottid carries a set of female and male
  reproductive organs
• These segments are released and are
  eliminated with the feces of the host.

                         *(Magnifications are based on a 35mm
                         slide image of 24mm in the narrow
     • Strobilation: asexual
      process of forming
     • New proglottids are
      continuously formed in the
      neck just below the scolex
     • Along the length of the worm
      the proglottids increase in
      size and maturity, developing
      from premature (B) to mature
      (C, carrying fully functional
      and active sexual organs), to
      the “gravid” stage (D) in
      which essentially the entire
      proglottid is filled with the
      uterus and eggs
The tegument
        • Cestodes do not have a
          mouth or any form of
        • The entire uptake of
          nutrients occurs through
          multinucleate syncytial
        • In reflection of this
          important role in uptake
          the absortive surface is
          highly enlarged by small
          microvilli or microtriches
        • Microfilaments (actin
          polymers) are the
          molecular backbone of
            Developmental stages: the egg
         Eggs              larval stages (IH)                 adult forms (DH)             Eggs
                                                             •With very few exceptions vertebrates are the
                                                             final host harboring the adult tape worms
                                                             •Many invertebrates and vertebrates are
                                                             parasitized as intermediate hosts
                                                             •The embryonate egg contains the oncosphere
                                                             a larva that will penetrate the intestinal wall
                                                             after eggs are swallowed by intermediate host
                                                             •The oncospheres of eucestoda have three
                                                             pairs of hooks which makes it easy to identify
Diagram of oncosphere of Hymenolepis diminuta, dorsal view
                                 The egg of the pseudophyllidean
                                 tapeworm (left) has a thin shell wall and
                                 an operculum, which on hatching opens
                                 to release the free swimming larvae. In
                                 contrast, the egg of the cyclophyllideans
                                 tapeworms (right) has a very thick,
                                 resistant egg shell, with no operculum.
                                 The eggs of T. saginata and solium are
                                 similar. CDC
Developmental stages
          • The zygote develops into
            an oncosphere
          • In some species with
            aquatic hosts the inner
            envelope develops into a
            ciliated epithelium.
          • These motile coracidia
            have to be taken up by an
            intermediate host within a
            short time
          • Once inside the gut of the
            host the oncosphere
            sheds the ciliated layer
            and invades and
            differentiates into a
                        Developmental stages
                                                         • In pseudophyllidean
                                                           cestodes the larvae look
                                                           fairly similar to the adult.
                                                           The first host is infected
                                                           by a procercoid which
                                                           still carries the larval
                                                         • In the second host a
       (D. latum)         (D. latum)                       plerocercoid forms (there
                                                           is no asexual
                                                         • The cyclophyllidean
                                                           larvae are more complex
                                                           and come in a quite a
                                                         • The medically important
                    (T. solium)                            larvae are cysticercoid,
                                                           cysticercus and hydatid
                                                           (some of these larvae
(Hymenolepis sp.)                      (E. granulosus)     provided amplification)
Developmental stages

                                                       • Most
                                                         cestode larvae (or
                                                         metacestodes) are
                                                         some form of a liquid
                                                         filled bladder with an
                                                         invaginated scolex
                                                         (and this theme is
                                                         the varied in many
                                                       • In most cases the
                                                         adult is very well
                                                         adopted to the host
                                                         and causes no
                                                         damage, it is the
   The cyst was defined as a hydatid cyst after the
   pathological diagnosis. Having been reevaluated       larvae that are
   as a primary focus, liver profile and abdominal
   ultrasonography findings were normal; and
   serological tests results were negative. Hydatid      pathogens
   cyst in inguinal region was accepted as a primary
   cyst. Gulten Kiyak, Mehmet Ozer, Recep Aktimur
   & Ahmet Kusdemir: Primary Hydatid Disease of
   the Soft Tissue: The Internet Journal of Surgery.
   2006; Volume 8, Number 2.
    Development in the Definitive host
     Eggs     larval stages (IH)   adult forms (DH)   Eggs

• In the small intestine of the DH, the juvenile worm excyst,
evaginate, or both.
• Digestive enzymes from the host „s gut may play a role in the
release of the organisms from their cyst. Temperature is also
• Development of the strobila is influenced by size of the
juvenile, worm species, size and diet of the host, presence of
other worms, and immune and/or inflammatory state of the host
• Carbohydrates in the diet are important for the growth of the
worm. Polysaccharides able to release glucose are ideal.
Glucose or a disaccharid containing glucose, such as sucrose
are not as good.
• As a worm approaches maximal size, growth rate decreases.
• T. saginata may live in a human for more than 30 years.
• Order pseudophyllidea: have scolex with bothria; the sperm whale tapeworm, H.
physesteris, can be > 30 m long; the genital pore and uterine pore are located on the mid-
ventral surface, and the ovary is bilobed ("dumbbell-shaped"); each segment has 4-14
complete sets of genitalia, can be up to 45,000 segments in a worm
          • Diphyllobothrium sp.

           Diphyllobotrium latum
• Order cyclophyllidea: most important group of tapeworms of humans and
domestic animals, multiple proglottid, scolex ("head") with four suckers. Proglottids have a
yolk gland or vitellarium posterior to the ovary; can be small (a few mm's) or large (up to 10
m); mammals serve as intermediate hosts
          • Family Taeniidae:Taenia saginata, Taenia solium, taenia multiceps;
          Echinococcus granulosus, E. multilocularis
          • Family Hymenolepididae: Hymenolepis diminuta, Hymenolepis nana,
 Diphyllobotrium latum - the fish tape worm-
                                               Life cycle
                                                            • Common in fish
                                                              eating carnivores
                                                              with little host
                                                              specificity. Salmon,
                                                              trout, perch, white
                                                              fish, eel, pike, etc.
                                                            • Adults get quite long
                                                              (10 m) and shed up
                                                              to a million eggs per
                                                            • Eggs must reach
                                                              water for
                                                            • After several days a
                                                              coracidium hatches
                                                              through the
                                                              operculum and is
                                                              eaten by a copepod

Diphyllobotrium latum
 - the fish tape worm

                •   The coracidium is eaten by the
                    copepod (First Intermediate Host)
                •   It looses its ciliated coat and once
                    through the intestine and into the
                    hemocoel, it develops into the
                    procercoid in 3 weeks ( 500 m)
                    with a cercomer at the posterior
                •   The copepod is weakened by the
                    parasite and less motile
                •   The procercoid can not develop
                    any further until is eaten by a fish.
                •    The larvae penetrate the small
                    fish gut (Second Intermediate
                    Host) and migrates in the muscle
                •   Here it grows and matures into the
Diphyllobotrium latum - the fish tape worm

                   •   Mature plerocercoids can be easily seen
                       as white masses in uncooked fish
                   •   If host fish is eaten by other fish
                       plerocercoids will migrate into muscle of
                       new fish host (paratenic host)
                   •   The plerocercoid develop into immature
                       and then into mature adult tapeworms in
                       the small intestine.
                   •   About 9 million people infected (was
                       wide spread in northern Europe and
                       Japan, more cases in the US due to
                       sushi, sashimi and ceviche)
                   •   Infection occurs through raw fish dishes
                       or handling (tasting) of fish dishes
                       before cooking
                   •   Infection rate can be locally quite high,
                       especially when untreated sewer is led
                       into lakes (there are also reservoirs in
                       many carnivores)
                Diphyllobotrium latum -
                       the fish tape worm

                                                  • Definitive host:fish-eating
                                                    carnivores:dogs,bears, humans, etc.
                                                  • Infection of humans cause no or little
                                                    symptoms (abdominal discomfort,
                                                    nausea diarrhea are rare)
                                                  • The parasite takes up large amounts of
                                                    Vitamin B12
                                                  • In patients with genetic deficiencies in
                                                    Vit B12 uptake the parasite competes
                                                    effectively for the entire vitamin leading
                                                    to severe pernicious anemia
                                                  • Geographic distribution: Northern
                                                    Europe, Chile, Japan, Korea North
Diphyllobothrium latum (broad fish                  America
m_latum.jpg/view. html
Diphyllobotrium latum - the fish tape worm
                      • Diagnosis through detection of
                        characteristic eggs in feces
                      • These eggs are oval or ellipsoidal
                        an operculum (arrows) at one end
                        that can be inconspicuous. At the
                        opposite end there is a small knob
                        that can be barely discernible
                      • The eggs are passed in the stool
                        unembryonated. Size range: 58 to
                        76 µm by 40 to 51 µm.
                      • Treatment with praziquantel

                                     • Proglottids of
                                     latum. These proglottids tend
                                     to be passed in strands of
                                     variable length in the
                                     stool. The proglottids tend to
                                     be broader than long. Image
                                     contributed by Georgia
                                     Division of Public Health.
                    TAENIA SAGINATA
• Beef tapeworm                                                                                                           Taenia
• Ranges in length from 6-30 ft                                                                                           saginata
• Geographic distribution:                                                                                                worm.
 Most common where poor sanitation
 and no inspection of meat combine
• Africa and South America
• Transmission: Ingestion of larval
 form in undercooked beef
• In N. America 1 in 100 is infected. In
 third-world nations could be up to 10%
• No symptoms or some abdominal
• Diagnosis: finding eggs or
 proglottids in feces

                            (A) Adult T. saginata in the ileum of a 25-year-old patient. Reflux of barium into the terminal ileum during
                            a barium enema examination revealed a markedly elongated ribbon-like radiolucent shadow representing
                            the adult tapeworm. (B) Adult T. saginata recovered intact following its passage after a vermifuge was
                            administered. Note the extraordinary length of this worm, which may at times reach 20-30 feet.
Taenia life cycle
                    •   Humans are the only
                    • The eggs can survive
                     for days to months in
                     the environment
                    • The adult worm
                     attaches by their
                     scolex to the human
                     small intestine.
                    • The adults produce
                     proglottids passed
                     with stool
                    • The eggs are released
                      after the proglottids
                      are passed with the
                               TAENIA SOLIUM

                                                                                                       The armed
                                                                                                       scolex of T.
                                                                                                       solium (note
                                                                                                       hooks on top
                                                                                                       of scolex).

• T. solium has a scolex (A) with four suckers and a double
 crown of hooks, a narrow neck, and a large strobila (2-4 m) (B)
 consisting of several hundred proglottids.
• About 2 months after ingestion, proglottids begin to detach from
 the distal end and are excreted in the feces.
• Each segment contains 50-60,000 fertile eggs.                Taenia pisiforme, Scolex. Hakenkranz ähnlich
                                                               dem der T. solium (Mit freundlicher Genehmigung Roche
                  The Lancet (2003) 361: 547                   iforme_r.jpg
                             TAENIA SOLIUM
                             •  Endemic in less developed countries
                               where pigs are raised as food source. Latin
                               America, most of Asia, sub-saharan Africa,
                               and parts of Oceania.
                             • Infection with the adult forms of the
                               parasite produces similar symptoms to
                               infection with T. saginata.

                                                Cysticerci: (A) as seen in infected
                                                pork; (B) excised into a Petri dish.
                                                The white dot in each cyst
The Lancet (2003) 361: 547                      corresponds to the scolex. The
                                                Lancet (2003) 361: 547.
                          Human cysticercosis
                 When humans plays the role of the
                        Intermediate Host
• Larval stages develop in the human host
• Humans acquire cysticercosis through faecal-oral contamination with T. solium
•    The oncosphere in the eggs is released by the action of gastric acid and
    intestinal fluids
•    Cross the gut wall and enter the bloodstream
•    They are carried to the muscles and other tissues
•    They encyst as cysticerci at small terminal vessels (1 cm) (A) and (B)
•    Neurocysticercosis and ophtalmic cysticercosis

                                                                       MRI of multiple
                                                                       cysts. Image
                                                                       courtesy of the
                                                                       Centers for Disease
                                                                       Control and
       Racemose Cysticercosis-MRI
• The parasite infects the CNS
• Epileptic seizures (58-80% when parenchymal
 brain cysts).
• Intracranial hypertension, hydrocephalus, or both.
 This syndrome is related to the location of parasites
 in the cerebral ventricles or vasal cisterns.
• Occasionally a cyst may grow larger (giant cyst)
• Racemose form: high mortality. Large translucent
 vesicle lobulated without scolex which develops in
 the basis of the brain or in the ventricles.
 Sometimes several small vesicles surround a
 pedicle like a bunch of grapes.
• Geographical variation in clinical manifestations                               From: NEJM (2001) 345:879

Neuroimaging: MRI of viable (A) and degenerating (B) cysts and CT of calcified cysticerci. The Lancet (2003) 361: 547
                 Cysticercosis diagnosis

• Serologic diagnosis:
     • Antibody assays for cysticercosis: 8
      kDa antigens, GP50, FAST-ELISA
      with the 8 kDA antigen
     • Antigen-detection assays:
      circulating antigens means live
      parasites. Ongoing viable infection.      MRI showing parenchymal (A) and
      Monoclonal antibodies seem to             extraparenchymal (basal ccs) (B) viable NCC.
      detect AGs in CSF.
     • Antibody assays for taeniasis:                                          MRI showing
                                                                               calcified cyst with
      TSE33 and TSE38 were recognized                                          surrounding
      by a panel of taeniasis but not                                          edema
      cysticercocis, patient serum
• Neuroimaging diagnosis: CT and
 MRI provide objective evidence on
 number and location of cysticerci. Also
 their viability and the severity of the host
 inflammatory reaction.
               Cysticercosis treatment
• Treatment should be individualized based on
 cyst location, level of inflammation and clinical
• Therapy should include analgesics, antiepileptic
 drugs, cysticidal drugs, surgical resection of
 lesions and placement of ventricular shunts
• Parenchymal cysticercosis with viable cysts:
 Albendazole 15 (mg/kg/day) with
 dexamethasone (0.1 mg/kg/day). Praziquantel.
• Subarachnoid ccs: antiparasitic therapy
• No reason to use antiparasitic drugs to treat
 dead calcified cysts. Symptomatic therapy.
• Surgical therapy: ventricular shunting to resolve
 hydrocephalus. Also excision of giant cysts or
 intraventricular cysts

• It is not possible to acquire NCC by eating pork!
• Ingestion of infected pork only causes adult
  tapeworm infestation: taeniasis. WHY?
• Infected pork contains only the larval cysts that
  develop into adult worms in the human intestine
• What is that transmits CCS?
• The eggs
• Most common source of infective eggs?
• A symptom-free tapeworm carrier in the household

• Echinococcus multilocularis:
  alveolar echinococcosis.                  Invasive solid
  lesions of firm consistency, full of connective tissue and a
  jelly-like material.

• Echinococcus granulosus: cystic
  echinococcosis.            Produces cystic lesions
          Echinococcus granulosus -
                   the dog tape worm

•   Adult E. granulosus adult worms live in the intestine of dogs
•   They produce eggs which are shed with the feces
•   Eggs are infective to herbivores (and humans)
Echinococcus granulosus

           • The oncosphere
             penetrate intestine
             of intermediate host
             and develops into a
           • Hydatides are
             spherical fluid-filled
             cysts surrounded by
             a granuloma formed
             by the host
The Hydatid Cyst
       •   The cyst is lined by a multilayer parasite tissue
           with the innermost layer being the germinal layer
       •   This layer is a undifferentiated “stem cell” layer
           that can spawn the formation of “brood capsules”
           which are themselves lined by GL
       •   The daughter cysts (the encircled body) "bud"
           into the center of the fluid-filled cyst.
       •   This is a very small portion of the cyst which may
           become quite large.
       •   Each of the smaller bodies will develop into
           diminutive tapeworms should this be eaten by a
           definitive or final host such as a canine.
The Hydatid Cyst
        •   Thousands of
            protoscolices can fill the
            hydatid (hydatide sand)
        •   Protoscolices are the
            infective stage for dogs
        •   Hydatides usually grow
            slowly but steadily (1-5
            cm per year)
        •    They are usually well
            tolerated until their size
            becomes a problem or
            they rupture
        •   Cyst rupture or leakage
            can result in allergic
            reactions and metastasis
Cystic hydatid disease
                 • Hydatides can be
                   found in several
                   organs but are most
                   frequent in the liver

         Hydatid cyst in human:
Cystic hydatid disease
             • Liver cysts cause liver
               swelling, right epigastric
               pain, nausea, vomiting
             • Obstruction of bile ducts and
               blood vessels can cause
               cholangitis, jaundice,
               cirrhosis and portal

           This upper abdominal CT scan shows multiple cysts in the liver, caused
           by echinococcus. Note the large circular cyst (seen on the left side of
           the screen) and multiple smaller cysts throughout the liver.
Cystic hydatid disease
       •   Lung cyst are often well tolerated but
           obstruction and or rupture can cause
           chestpain, cough and dyspnea
       •   The first symptoms of brain cyst is often
           focal epilepsy
       •   Diagnosis is by serology, radiology, CT
           scans and sonograms.
       •   Treatment is surgical. Prognosis
           depends on size and location of
           hydatide (mortality is around 5-10%)
       •   Hydatide is often injected with sterilizing
           fluids to avoid “metastases”
       •   Benefit of chemotherapy is inconsistent
Echinococcosis control
           •   Sylvatic and domestic strains.
           •   Strains adapted to dogs &
               sheep are more aggressive
               upon human infection
           •   Ecchinococcosis can be
               locally quite important
           •   Control of feral dogs, limit
               access of dogs to sheep offal,
               treat pet dogs regularly
           •   Effective control programs in
               many countries including
               New Zealand, Tasmania,
               Cyprus and Iceland
Echinococcus multilocularis - the
        fox tape worm
                     •   Sylvatic zoonosis in
                         Europe and northern
                     •   Fox is final host, life
                         cycle similar to E.
                     •   Humans get infected by
                         eating contaminated
                         berries and mushrooms
                         collected in forests
                         populated by foxes
Hymenolepis nana -
the dwarf tape worm
                     • Hymenolepis nana
                       occurs relatively
                       frequently world
                       wide and is usually
                       an infection of
                     • An intermediate
                       host is not required
                       and autoinfections
                       occur frequently
                     • Cysicercoids
                       develop in the
                       lymphatics of villi
                     • Alternatively
                       infection through
                       cysticercoids in
                       insects that
                       contaminate grains
                       or cereal
Hymenolepis nana -
the dwarf tape worm

         • Usually asymptomatic (very
           high burden can lead to
           unspecific gastrointestinal
         • Infections are cleared with
         • Diagnosis by demonstration
           of characteristic eggs
         • (accidental infections with H.
           diminuta the rat tape worm)
                      STAGE FOUND      COMM ON
      SPECIES                                          PATHOLOGY                   THERAPY
                        IN HUM ANS        NAME
Diphylobot rium lutum Adult        Fish tapeworm     Pernicious anemia       Niclosamide; Praziquantel
Hymenolepis nana   Adult           Dwarf tapew orm   Rarely sy mptomatic     Niclosamide; Praziquantel
Taenia saginata    Adult           Beef tapew orm    Rarely sy mptomatic     Praziquantel
Taenia solium      Adult           Pork tapew orm    Rarely sy mptomatic     Niclosamide; Praziquantel
                   Larv ae                           Brain and tissue        Albendazole; Surgery
                                                     cy sts
Echinococcus       Larv ae         Hy datid cy st                       ts
                                                     Solitary tissue cy s    Surgery; Albendazole
granulosus                         disease
Echinococcus       Larv ae         Alv eolar cyst    Multilocular            Surgery; Albendazole
multilocula ris                    disease           cy sts

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