MIDTERMS

• Taenia saginata


  Beef tapeworm of humans
• Taenia saginata is cosmopolitan in distribution
• Humans serve only as definitive host and never as intermediate hosts for Taenia saginata
• Human cysticercosis due to Taenia saginata does not occur
• Adult Taenia saginata


  • Inhabits the upper jejunum
  • Can live for up to 25 years
  • Derives nourishment from intestinal contents
  • Measures 4 to 10 m in length
  • May have 1,000 to 4,000 proglottids
• Taenia saginata scolex


  • Cuboidal, measures 1–2 mm in diameter
  • Has four prominent acetabula
  • Devoid of hooks or a rostellum
• Development of proglottids in Taenia saginata

  Attached to the scolex is a short neck from which a chain of immature, mature, and gravid proglottids develop
• Mature Taenia saginata proglottids


  • Approximately square in shape
  • Contain mature male and female reproductive organs
  • Have two large lobes of ovaries and a median club-shaped uterus
  • Have 300 to 400 follicular testes scattered throughout
• Gravid Taenia saginata proglottids


  • Longer than they are wide (16- 20 mm by 5-7 mm)
  • Most distal from the neck
  • Uterus is distended with ova and has 15 to 20 lateral branches
  • Genital pores of proglottids are irregularly alternate
• Taenia spp. ova


  • Spherical or subspherical in shape, measuring 30 to 45 μm in diameter
  • Brownish in color, with a thick embryophore which appears striated because of numerous pits
  • Inside the eggshell is the oncosphere or embryo provided with three pairs of hooklets
• A gravid Taenia saginata proglottid contains 97,000 to 124,000 ova
• Annually, a Taenia saginata worm may pass out 594,000,000 ova
• Release of Taenia saginata eggs

  1. Gravid proglottids undergo apolysis and are either passed out with the feces or actively crawl out of the bowel to the external environment

  2. With apolysis of gravid segments, eggs are released and they remain viable in the soil for weeks
• Development of Cysticercus bovis in cattle


  1. Upon ingestion of the T. saginata eggs by cattle, the oncosphere is released

  2. The oncosphere actively penetrates the intestinal mucosa, enters a venule, and is carried to other parts of the body

  3. It typically enters a muscle fiber and develops into an infective stage called Cysticercus bovis in 2 months
• Cysticercus bovis


  • Ovoidal, milky white, about 10 mm in diameter
  • Has a single scolex invaginated into a fluid-filled bladder
• Development of adult Taenia saginata in humans

  1. Humans readily become infected when these encysted larvae are ingested from raw or improperly cooked beef

  2. The larva is digested out of the meat, and the scolex evaginates to attach to the mucosa of the small intestines where it will become mature in about 12 weeks
• Usually, only one adult Taenia saginata tapeworm is present in infections
• The adult Taenia saginata tapeworm


  Seems to be irritated by alcohol, and passage of proglottids sometimes results after a drinking bout
• Humans are not suitable intermediate hosts for Taenia saginata
• Taeniasis


  Infection with the adult tapeworm
• Taenia solium


  Pork tapeworm of man
• Taenia solium has a cosmopolitan distribution
• Man may serve as both a definitive host and an intermediate host for Taenia solium
• Adult Taenia solium


  • Inhabits the upper small intestines
  • Shorter than Taenia saginata and has less number of proglottids (2 to 4 m in length, 8,000 to 10,000 proglottids)
• Taenia solium scolex


  • Has four acetabula, but is smaller (1 mm) and more spherical than Taenia saginata
  • Carries a cushion-like rostellum with a double crown of 25 to 30 large and small hooks
• Taenia solium proglottids


  • Presence of an accessory ovarian lobe
  • Absence of a vaginal sphincter
  • Smaller number of follicular testes (100- 200)
  • Gravid proglottids characteristically contain 7 to 13 lateral branches
• Taenia solium proglottids are relatively less active than the proglottids of Taenia saginata
• Taenia solium gravid proglottid


  Contains approximately 30,000 to 50,000 ova
• Development of Cysticercus cellulosae in pigs

  1. The Taenia solium eggs are ingested by hogs and the oncospheres are released in the intestines

  2. The oncosphere penetrates the intestinal mucosa to typically encyst in muscles as cysticercus cellulosae
• Cysticercus cellulosae


  • Oval, translucent, has an opaque invaginated scolex with four suckers and a circlet of hooks
  • Usually encapsulated with adventitious host tissue, but may be unencapsulated in the vitreous humor and in the brain
  • Can attain a full size of 5 mm in 10 weeks
• Human infection with Cysticercus cellulosae

  1. Can be acquired through fecal-oral route by ingesting Taenia solium eggs from contaminated food or drink

  2. Individuals harboring the adult Taenia solium can infect themselves (autoinfection) due to poor hygienic practice
• The patient may complain of intraorbital pain, photopsia, and blurring or loss of vision
• Taeniasis


  Specific diagnosis rests on identifying the characteristic proglottids, eggs, or scolex
• Cysticercosis


  Neurocysticercosis may be suspected in a patient coming from an endemic area with epileptic seizures without associated systemic symptoms
• Cysticercosis diagnosis


  • Concomitant infection with T. solium adult occurs only in 25% of cases
  • If a patient has subcutaneous cysticerci concomitant with neurologic symptoms, this provides presumptive evidence for neurocysticercosis
  • CSF abnormalities such as an elevated protein, reduced glucose, and increased mononuclear cells may be seen
  • Computed axial tomography (CAT) scans and nuclear magnetic resonance imaging (MRI) are useful for localizing cysticerci and evaluating the pathology before and after treatment
• CAT scan patterns for cysticercosis

  • A round low-density area without surrounding enhancement after administration of contrast dye (shows a viable larva with no inflammation)
  • Ring-like enhancement after injection of contrast dye (shows a dead larva)
  • A small calcified area within a cystic space (shows a dead scolex)
• Ophthalmic cysticercosis


  Can be diagnosed through the visualization of the cysticerci using ophthalmoscopy but the procedure may induce movement and/or evagination of the scolex
• Muscular and subcutaneous cysticerci

  Usually palpable and can be recovered through tissue biopsy for histopathologic processing
• Serologic tests for cysticercosis

  • Serum and CSF enzyme-linked immunosorbent assay (ELISA) and electro-immuno transfer blot (EITB) or Western blot for specific IgG and IgM anticysticercal antibodies (have a sensitivity of 75 to 100% using a partially purified glycoprotein antigen to detect antibodies)
  • Dot-ELISA test is a very good screening test for cysticercosis (uses crude antigen from the cysticerci obtained from pigs)
  • Recent studies are looking into the use of antigen B of cysticercus cellulosae as a useful adjunct in diagnosis
• Taeniasis treatment


  The drugs of choice are praziquantel and niclosamide