Taenia

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Taenia
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Cestodes (Tape Worms)

• Taenia solium (pork tapeworm) - Cysticercus
• Taenia saginata (beef tapeworm)
• Diphyllobothrium latum (fish tapeworm)
• Echinococcus granulosus (unilocular hydatid)
• Echinococcus multilocularis (alveolar hydatid)
• Hymenolepis nana (dwarf tapeworm)
• Hymenolepis diminutia
• Dipylidium caninum

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General Structure of Tapewormv

• Head region (scolex) contains suckers and hooks
  used to attach to a host organism.
• Proglottids square body segments used for
  reproduction.

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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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Immature Segment

• note that the reproductive organs are just
  beginning to differentiate.
• (Carmine stained)

Developing reproductive organs
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Mature Segments (Proglottids)

• Tapeworms are Hermaphroditic

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TaeniasisGeographic Distribution

• Worldwide, depending on dietary habits, and
  quality of cattle and pork farming.

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Taenia saginata and T. soliumScolex And
Proglottids
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Taenia saginata The beef tapeworm
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Cysticerci - heart of cow Veterinary
Pathology Laboratory, Univ. Penn
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T. saginata

• Definitive Host Human
• Intermediate Host Cow

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Adult Taenia saginata

• Scolex
• Immature proglottids
• Mature proglottids
• Gravid proglottids

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Taenia saginata scolex

• Suckers

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Gravid Proglottid of Taenia saginata
Uterine branches
Uterus
The central uterus of T. saginata has more than
12 branches on a side
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Embryonated, infectious taeniid eggs

• Cannot distinguish species of Taenia tapeworms
• based on morphology of eggs

• Egg Envelope

Hexacanth larva Hooklets
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• Pathogenesis None
• Clinical Disease None in humans

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Diagnosis

• 1. Find eggs or proglottids in stool
• 2. Identify species based on
• proglottid morphology, after
• formalin and India Ink
• 3. Identify scolex

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Drug of Choice

• Praziquantel
• Mode of Action
• Increases permeability of flatworm tegument to Ca
  2 ions,
• Causing muscle tetany and worm detachment.

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Prevention and Control

• 1. Sanitary disposal of human feces

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• 2. Prevent cows from coming into contact with
  human feces, ie good sanitation and physical
  restraints.
• 3. Freeze and/or cook all beef until well-done
• 4. Federal meat inspection programs (muscle exam
  or serum ELISA specific to larval stage).

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Taenia soliumThe Pork Tapeworm
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Taenia solium scolex
Hooks
Suckers
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Taenia solium (Pork Tapeworm) Morphology

• Adult Worm
• 2-4 m long,
• 700-1000
• segments
• Scolex
• Neck
• Immature segment
• Mature segment
• Gravid segment

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Gravid proglottid Taenia solium

• Uterine branches number less than 10 per side

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Cystcercus cellulosae in Muscles of Pigs
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Cysticercus cellulosae

• It is soybean-like in shape, with the
  small scolex invaginated into the translucent
  cyst (left).
• The scolex evaginated from the cyst (right).

Cysticercius cellulosae
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Taenia eggs

• The eggs of Taenia saginata and T. Solium are
  morphologically indistinguishable.

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Teania solium

• Two different forms in humans
• Human taeniases
• Human cysticercosis

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Taeniasis life cycle
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Life Cycle
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Basics (1)

• Complex two-host life cycle
• Human beings are the only definitive host (small
  intestines - 2-4 meters long -800-1000 segments)
• Both humans and pigs can act as intermediate
  hosts (larvae or cysticerci)
• Most common in Latin America, Africa and India -
  400,000 people have symptomatic
  neurocysticercosis in Latin America

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Basics of the infection cycle

• Faecal-borne infection
• Tapeworm larval cyst (cysticercus) is ingested
  with poorly infected meat
• Larva escapes the cyst and attaches to the mucosa
  by the scolex
• Feces are contaminated with eggs (persist for
  several days in the environment) - consumed by
  pigs (eggs are hatched and form cysticerci

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• Humans are the only definitive host
• Pigs - intermediate host (cysticercal stage)
• However Humans - also can be the intermediate
  host - causing cysticercosis (neurocysticercosis)
  if they ingest eggs

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Human infection - taeniasis

• The scolex attaches to the mucosa and begins
  forming segments (proglotids)
• After two months of infection, gravid proglotids
  begin to detach from the distal end - excreted in
  the feces
• Each segment contains 60,000 eggs
• Worm causes only minor inflammation to the
  intestine (mild symptoms - abdominal pain,
  distension, diarrhea and nausea - or none at all)

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Taeniasis Diagnosis

• Symptoms
• History of eating undercooked beef or pork
• Recovery of proglottids and/or eggs in the stool

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TaeniasisTreatment and Prevention

• Treatment
• Praziquantel scolex expulsion is essential
• Prevention
• Adequate cooking of meat
• Freezing meat below 10º C

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Human infection - cysticercosis

• Faecal-oral contamination with T. solium eggs
  from tapeworm carriers
• Internal autoinfection is also possible
• The invasive oncosphere (embryos) in the eggs are
  liberated by the action of gastric acid and cross
  the bowel wall (remember - cysticerci are too big
  to cross the bowel wall)
• They establish at small terminal vessels
  (muscles, brain, eye) where they grow to about
  the size of 1 cm in 2-3 months

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Human cysticercosis

• Muscle - small, palpable, movable nodules -
  chests and arms - mild or no symptoms
• Ophthalmic cysticercosis - intraocular cysts
  floating freely in the vitreous humor - decreased
  visual acuity
• Neurocysticercosis - most symptoms are because of
  the inflammatory reaction associated with cyst
  degeneration (that may take years to happen) -
  epilepsy, hydrocephalus, encephalitis, meningitis

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CysticercosisDisease
Cerebral cysticercosis
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Cysticercosis Disease

• Cardiac cysticercosis

Ocular cysticercosis
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Pathogenesis

• Space-Occupying lesion
• Local Immunologic Reaction

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Diagnosis

• Must differentiate between cysticercosis and
  other possible lesions (benign cysts, solid
  tumors, etc.)
• 1. Biopsy whenever possible
• 2. Physical (palpation) and radiological evidence
• 3. Enzyme-linked immunoblot serological test,
• can be as high as 98 sensitive, 100 specific.
• 4. MRI

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Treatments

• 1. Surgical removal of cysticercus when
  appropriate
• 2. Steroids (e.g., dexamethazone) during time of
• neurological symptoms
• 3. Anticonvulsants (e.g. Dilantin)
• 4. Antiparasitic antibiotics Praziquantel or
  albendazole
• steroids anticonvulsants
• if multiple symptomatic cysticerci or inoperable
• (still being studied)

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Epidemiology

• Affect millions of individuals - 2.5 million
  people worldwide carry the T. solium and 20
  million are infected with the cysticerci
• Endemic villages - up to 25 are seropositive and
  10-18 have neurocysticercosis

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Methods for controlling

• taeniasis/cysticercosis
• Pig vaccination
• Pig treatment
• Human carriers mass treatment
• Health education

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Economic factors - domestic pig raising

• Domestic pig raising, taeniasis and human
  cysticercosis are intimately related - pigs are
  cheap and easily marketable - convenient source
  of meat or money
• Pigs also eat pasture and garbage
• Endemic regions - 30-60 of pigs are infected
• Pig production has doubled in the last 20 years
  in Africa
• Owners usually detect infection in vivo and them
  sell these cheaper pigs to unofficial slaughter
  houses or kill them at home

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Health education

• Association of cysticercosis prevalence and
  unsanitary rearing of pigs, inability to
  recognize infected pigs and insufficient
  knowledge of transmission
• Education hand washing, defecating in fields,
  corralling of pigs
• Ex. Community in Mexico - although almost
  everybody could identify cysticercosis in pigs,
  only 0.7 knew how pigs were infected

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Eradication

• Pros human is the only carrier, there a
  relatively simple treatment
• Other issues
• 1) Technical - lack of a simple diagnosis, lack
  of an easily available treatment (costs)
• 2) Societal poor community cooperation and
  sanitary education
• 3) Political low priorities and debatable
  strategy
• CDC - eradication cannot be achieved in the near
  future - only regional elimination

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Difficulties to implement control programs

• (ii) Taeniasis is also a mild infection, which
  does not prompt the carrier to get rid of a
  tapeworm even when it is diagnosed.
• (iii) Traditional laboratory diagnosis of
  tapeworm infection in humans has poor accuracy
  and other modern coproantigen tests have not been
  introduced to the market and are expensive
• (iv) Treatment rates are frequently low
  -appropriate medicines are not available in many
  endemic areas
• (v) Several human behavioral factors -
  traditional preferences for raw pork consumption
  and indiscriminate, unsanitary defecation,
• (vi) Inadequate local levels of information on
  taeniasis/cysticercosis
• (vii) There is clear economic motivation for
  small scale pork producers to minimize commercial
  losses associated with infected carcass
  condemnation at official slaughter

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Political will

• The public health impact of human cysticercosis
  in some regions is serious (significant social
  and financial costs)
• Neurocysticercosis can potentially affect any
  person (rural or urban area)
• Contamination with eggs can also be common in
  urban centers
• Control measures can be implemented regionally
• Efficacy of schemes can be measured in sentinel
  or slaughtered pigs

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Is this disease only a consequence of poverty?

• Eradication of extreme poverty - would reduce
  subsistence pig rearing
• Achievement of universal primary school education
  - increase knowledge about risky behaviors in
  relation to T. solium transmission
• Gender equality and empowering women - decrease
  risk of taenia infection at home - reducing
  consumption of contaminated meat and personal
  hygiene
• Combating major infection diseases
• Improvement of sanitation

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thanks for your attention