Major Attributes:

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Major Attributes

• Endoparasitic.
• Acoelomates
• Body is covered by tegument.
• Anterior end is a scolex.
• Body segments called proglottids.
• Hermaphroditic.

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General Structure of Tapeworm
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Cestoidea

• Some species can reach lengths of up to thirty
  meters. (Hexagonoporus from whale)
• Life cycles require one, two or three
  intermediate hosts.
• Many life cycles involve man and domestic
  animals.

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Tapeworm Structure

• Scolex - Attachment organ
• Zone of Proliferation - Undifferentiated area
  behind the scolex (neck region)
• Strobilia - Chain of segments (proglottids)
• Immature proglottids - developing reproductive
• Mature proglottids mature reproductive organs.
• Gravid proglottids contain eggs in the uterus.

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Scolex
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Taenia sp. Scolex
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Four Types of Proglottids

• As proglottids are formed, they are pushed
  posteriorly. There are 4 regions.
• a. Zone of proliferation
• b. Zone of immature proglottids
• c. Zone of mature proglottids - area with
  sexually mature organs
• Gravid zone - area where proglottids contain
  eggs.

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Tapeworm Strobila

• Linear series of sets of reproductive organs
  (proglottids).
• Each mature proglottid contains male and female
  reproductive organs.
• New proglottids produced by strobilization which
  is a budding that occurs from the neck region
  (the zone of proliferation).

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Egg Release from Proglottids

• Apolysis - entire proglottid containing eggs is
  released or disintegrates releasing eggs.
• b. Anapolysis or Pseudopolysis- proglottids
  remains attached eggs are released through some
  uterine pore or tear in the gravid proglottid.
  c. Hyperapolysis - immature proglottid released
  and matures within the host.

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Tapeworm Scolex

• Scolex
• Most tapeworms have some type of attachment
  organ located at the anterior end.
• There are many adaptations including suckers,
  hooks, grooves and some tapeworms lack a scolex
  altogether. See page 301 for different types of
  scolices

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Types of Tapeworm Scolices

• Pseudoscolex is a distortion of the anterior end
  of the strobila.
• Acetabula - suckers is most common form
• Bothria - take the form of slits or grooves as in
  Diphyllobothrium latum
• Bothridia - often leaf-like muscular projections,
  usually in groups of four.

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Hymenolepsis diminuta scolex
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Scolex
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Rostellar hooks
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Trypanorhyncha scolex
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Tapeworm Tegument (integument)

• Adult tapeworms live in the digestive tract of
  host lack a digestive tract. The result is that
  the adult tapeworm must absorb all nutrients it
  gets through the integument.
• The integument is a highly specialized tissue
  with high metabolic activity covered by minute
  projections called microtriches (similar to
  microvilli). These increase surface area
  (increase absorption efficiency).

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Tapeworm Tegument (integument)

• Glycocalyx is a layer of carbohydrate containing
  macromolecules that coats the integument. It may
  enhance absorption of certain substances and at
  the same time inhibit activity of host enzymes
  that would digest the worm.

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Reproduction

• Tapeworms are hermaphroditic
• Each mature proglottid has both male and female
  reproductive organs.
• Cross fertilization gives genetic variability
• Protandry or androgyny - the testis matures
  before the ovary.
• Protogyny or gynandy - eggs develop before the
  sperm.

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How Fertilization Occurs

• In some cases fertilization occurs between the
  male and female gonads found in the same
  proglottid or in different proglottids of the
  same worm. (self-fertilization)
• In other cases, fertilization occurs between
  different worms in the digestive tract of the
  host.
• A few cestodes are dioecious

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Tapeworms

• All tapeworms are parasites
• Most parasitize wild animals few important
  parasites of men.
• Only orders Pseudophyllidea and other
  Cyclophyllidea contain tapeworms of importance to
  humans or parasites of man.

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Order Pseudophyllidea

• Bothria with longitudinal grooves form scolex

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Order Pseudophyllidea

• Contains many small species but also the largest
  species (Hexagonoporus from whale) commonly
  reaches 30 meters and the record is one 200 ft
  long
• These usually have some crustacean as first
  intermediate host and second intermediate host is
  often a Fish

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Diphyllobothrium latum)

• broad fish tapeworm -
• common in fish eating carnivores of northern
  Europe
• low level of host specificity or maybe several
  very similar species.
• Some areas 100 of population infected pg. 346
  2nd column

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Diphyllobothrium latum)

• Morphology -
• a. 30 ft long - shed 1 million eggs/day
• Scolex finger shaped with 2 bothria
• Proglottids wider than long (broad tapeworms

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Stages in Life Cycle

• Eggs passed in feces - in water develop hatch
  into coracidium.
• Crustacean (copepod) ingests coracidium.
• Coracidium loses cilia - reaches the hemocoel and
  develops into procercoid.
• Crustacean eaten by fish - develops into
  pleurocercoid (small fish eat crustacean, larger
  fish eat smaller fish)

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Stages in Life Cycle

• Definitive host becomes infected when it ingests
  infected fish.
• The pleurocercoid develops into adult to begin
  egg production in 1-2 weeks

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Epidemiology

• People become infected ingesting improperly
  cooked fish.
• Improper disposal of sewage into water - greater
  infection rate.
• Exporting of raw fish - improper cooking.

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Pathology

• Phyllobothriasis
• Many cases asymptomatic
• Pernicious anemia caused by tremendous absorption
  of Vitamin B12 by worm - Vitamin B12 needed to
  make RBC.

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Pathology

• Sparganosis-
• larval forms found in humans
• results of procercoids being ingested.
• pleurocercoids can migrate from gut and develop
  in organs of humans.
• use of using raw fish or amphibian as a poultice
  for medical treatment - pleurocercoid leaves fish
  or frog - enters skin of patient - eyes, vagina,
  pg. 329 Fig 21.9.

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Order Cyclophyllidea

• Compact single vitelline gland
• Scolex with 4 suckers
• Genital pore generally lateral
• Contains most tapeworms of birds and mammals.

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Family Taeniidae

• Largest cyclophyllideans of man - with exception
  of Genus Echinococcus.
• Contains most important medically to man
• Most species contain a rostellum which is
  non-retractable armed in most species - not in
  all
• Testis are numerous and ovary is bilobate mass
  near posterior margin of proglottid.

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Most Important Species

• Taenia solium
• Taeniarhynchus saginatus
• Echinococcus granulosus
• Echinococcus multilocularis

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Taenia solium -Pork Tapeworm

• Adult found in digestive tract of man.
• Potentially dangerous because man can become
  infected with larval stages.
• Intermediate hosts pigs ingest oncospheres which
  develop into cysticerci in tissues.
• Man becomes infected ingesting raw meat.
• Strobila commonly 6-10 feet long lengths of over
  30 feet reported

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Taenia solium - Morphology

• Scolex - 4 suckers rostellum armed with 22-32
  hooks.
• Gravid proglottis longer than wide - medial stem
  with 7 to 13 lateral branches as compared to
  15-20 lateral branches in Taeniarhynchus
  saginatus) See figure 21-15 pg. 332.
• Can not distinguish different Taenia eggs

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Taenia solium Biology

• Gravid proglottids passed in feces - flabby and
  inactive (unlike Taeniarhynchus saginatus.
• Eggs when ingested by pigs develop - into
  oncospheres and to cysticerci in muscles and
  other organs called measly pork.
• Person infected eating measly pork.
• Worm may live for 25 years.

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Taenia solium and saginata

• Gravid proglottids of Taenia solium has 7 - 13
  primary lateral branches.
• T. saginatus has 15 - 20 branches on each side.

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Taenia solium and T. saginatus
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Cysticercosis in humans

• Man must ingest embryonated egg (fecal
  contamination of food, hands, etc.
• or
• Gravid proglottid migrates or is moved by reverse
  peristalsis from intestine to stomach.
• Reenters intestine where eggs hatch - may lead to
  massive infection.

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Cysticercosis in humans

• Oncophere enters lymphatic and blood vessels.
• May develop in any organ most common it develops
  in the muscles.
• In eye usually results in irreparable damage.
• In Brain may result in paralysis, obstructive
  hydrocephalus, epilepsy - sometimes death.
• Inflammatory response (allergic) may be fatal.

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Cysticercosis in humans

• Oncophere enters lymphatic and blood vessels.
• May develop in any organ most common it develops
  in the muscles.
• In eye usually results in irreparable damage.
• In Brain may result in paralysis, obstructive
  hydrocephalus, epilepsy - sometimes death.
• Inflammatory response (allergic) may be fatal.

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Taenia solium cysterci in brain
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Prevention

• Properly cook pork.
• Proper disposal of human feces - and personal
  hygiene
• If adult worms in man - Need to treat humans to
  eliminate worms to prevent auto infection of
  cysticerci.
• Caution in using night soil on gardens

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Taeniahynchus saginatus

• Most common taeniid of humans.
• Occurs in all countries where beef is eaten.
• Morphology
• Scolex cuboidal up to 2mm in diameter - lacks
  hooks
• Long species - strobila up to 75 ft commonly 10 -
  15 feet.
• gravid proglottid with 15 - 20 lateral branches

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Biology of Taenia saginatus

• Gravid proglottids exit in feces or migrate out
  anal opening - very active in contrast to Taenia
  solium.
• Eggs are fully embryonated and infective to
  intermediate host. They may survive many weeks.
• Cattle becomes infected upon ingestion of
  embryonated eggs.

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Biology of Taenia saginatus

• Egg hatches hexacanth penetrates mucosa -
  intestinal venules - throughout body. Often
  enters muscle tissue.
• Forms cysticercus, known as cysticercosis bovis
  and meat is called measly beef.
• person becomes infected by eating improperly
  cooked measly beef.
• In man worm develops into mature adults.

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Pathology

• Reactions to the absorption of excretions of
  worms - host reaction.
• Blockage of digestive tract in high infection
  numbers
• Abdominal pain, headache, diarrhea, dizziness and
  others.
• Prevention includes Proper sanitation and
  Properly cooking beef.

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Echinococcus granulosus

• Genus Echinococcus contains smallest tapeworms in
  family Taeniidae.
• Juvenile forms capable of developing in humans
  resulting in hydatidosis.
• Echinococcus granulosis - has carnivores,
  especially dogs and other canines as definitive
  hosts.

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Morphology

• Adult 3-6mm long when mature
• Consists of Scolex - short neck usually 3
  proglottids (immature, mature, gravid)

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Hydatid cysts
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Hydatid Cysts
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Hydatid sand
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Mature protoscolex
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Echinococcus granulosis hydatid cyst

• Internal budding produces daughter cysts and
  brood capsules.
• Daughter scolices and brood capsules may break
  off sink to the bottom called Hydatid sand

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Epidemiology

• Sylvatic cycle - Wolf and some herbivore (Moose).
• Urban cycle - domesticated dogs - man (sheep,
  cattle and other herbivores).
• Tribes in Kenya - relish dog intestine - see pg.
  339 - first column

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Pathology

• May not become evident for many years.
• Pathology depends on location of hydatid cyst in
  host
• if vital organ severe damage - maybe death -
  brain, heart, liver.
• If non-restrictive tissues, hydatid may reach
  size containing 15 quarts of fluid. Should it
  upture, anaphylactic shock and death.

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Prevention

• Care not to ingest eggs from dog - Proper hand
  washing - children most likely to get infected
• Treatment of dogs.

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Echinococcus multilocularis

• Known from Europe, Asia, North America.
• Primarily associated with trappers and handlers
  of shed teams.
• Produces alveolar or multilocular hydatid cysts -
  infiltrates into surrounding host tissue like
  cancer.

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Prevention

• Prevented by avoiding dogs (foxes) etc in endemic
  regions, carefully washing strawberries,
  cranberries that may be contaminated with dog
  feces and regular worming of dogs liable to
  infection.

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Vampirolepis nana (Hymenolepsis nana)

• The dwarf tapeworm - most common tapeworm in man
• Cosmopolitan
• 97 of people in Moscow, 1 of people in
  Southeast U.S.

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Vampirolepis nana (Hymenolepsis nana)

• Intermediate host is optional. It can have a
  direct or an indirect life cycle
• Direct life cycle eggs ingested, hatch in
  duodenum, develop into cysticercoid and adult.
• Indirect life cycle involves grain beetle.
  Cysticercoid develops in beetle and man becomes
  infected by ingesting grain beetle.
• Common in areas where grain stored and people
  dependent upon it on a daily basis.

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Prevention

• Proper sanitation
• Properly cook grains