Neurosurgery notes/Infection/Cranial infection/Parasites/Worms/Cestodes (tapeworms)

Cestodes (tapeworms)

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Worms

Cysticercosis

Numbers

  • Most common parasitic infection involving the CNS
  • Most frequent CNS parasitic disease in the world.
  • Some low-income countries it is the most common cause of acquired epilepsy
  • Endemic in areas of Mexico, Eastern Europe, Asia, Central and South America, and Africa
  • The incidence of neurocysticercosis (encystment of larva in the brain) may reach 4% in some areas

Microorganism

  • Taenia solium
    • Pork tapeworm
  • The human is the definitive host of the adult worm.
  • The incubation period varies from months to decades
    • 83% of cases show symptoms within 7 years of exposure
  • Life cycle of T. Solium
    • 3 Stages
      • Larva
      • Embryo (or oncosphere)
      • Adult
  • T. solium can infect a person at two different stages forming 2 different diseases
      • As adult worm - causing Taeniasis
      • Infection with the adult worm (taeniasis—a parasitic infection)
      • Eating undercooked infested (measly) pork → The encysted larvae are released in the small bowel → the larvae then mature within the intestine into an adult over about 2 months.
      • The scolex (head) of the segmented adult worm attaches by means of four suckers and two rows of hooklets to the wall of the small intestine where the worm absorbs food directly through its cuticle.
      • Humans are the only known definitive hosts for the adult tapeworm, for which the GI tract is the sole habitat.
      • Proglottids (mature segments, each containing reproductive organs) produce eggs which are liberally excreted along with gravid proglottid segments in the fences.
      As the larva - causing Cysticercosis
      • Infection with the larva
      (a) Animals or humans become an intermediate host for the larval stage by ingesting viable eggs produced by the proglottid.
      (b) The most common routes of ingestion of viable eggs are
      1. Food (usually vegetables) or water contaminated with human faeces containing eggs or gravid proglottids (this is the means whereby pigs acquire the disease)
      1. Faecal-oral autoinoculation in an individual harbouring the adult form of the tapeworm due to lack of good sanitary habits or facilities
      1. Autoinfection by reverse peristalsis of gravid proglottids from the intestine into the stomach (unproven theoretical possibility)
      (c) In the duodenum of man and pig, the shell of the ova dissolves → newly hatched embryos (oncospheres) burrow through the small bowel wall to enter the lymphatics or vascular circulation → spread to
      1. Brain - see Neurocystecerosis
          • Involved in 60–92% of cases of cysticercosis.
          • Latency from ingestion of eggs to symptomatic neurocysticercosis: 2–5 years
      1. Skeletal muscle
      1. Eye
          • Immunologically privileged, like brain
      1. Subcutaneous tissue
      1. Heart
      (d) Once in the tissue of the intermediary host, embryos develop a cyst wall in ≈ 2 months (immature cyst) which matures in ≈ 4 months to a larva.
      (e) Larval cysts are usually rapidly eliminated by the immune system.
      (f) Many larvae die naturally within 5–7 yrs or with cysticidal therapy producing an inflammatory reaction with collapse of the cyst (granular nodular stage); these sometimes calcify (nodular calcified stage).
      (g) In pigs, the larva lie dormant in the muscle, “waiting” to be eaten, after which the cycle repeats.

Treatment

  • Praziquantel and albendazole.
  • Steroids are also given concurrently to reduce the edema that tends to occur initially during treatment with antihelmintics