Tapeworms (Cestodes)

Snapshot

• A 35-year-old man presents to the emergency department for seizures. Prior to developing seizures, he complained of a headache and was progressively confused. He eventually became nauseous and had multiple episodes of emesis. He recently emigrated from Mexico to the United States and did not have a seizure history. A CT scan of the head demonstrates parenchymal calcifications in the left parieto-occipital region. (Neurocysticercosis)

Introduction

• Definition
  • flat and hermaphroditic worms that are parasites of humans
    • may reside in the intestinal lumen or live in extraintestinal tissues
• Pathogens
  • Taenia solium
  • T. saginata
  • Diphyllobothrium latum
  • Echinococcus granulosus
• Pathogenesis
  • tapeworm contains a scolex (head) and proglottids (attached segments)
  • scolex of the tapeworm attaches to the intestinal tract and the adjacent proglottids inseminate, leading to the formation and release of eggs that are passed in feces
    • after an intermediate host ingests these eggs in feces, the eggs release an oncosphere
      • penetrates the gut and develops as cysticercus in tissues
        • humans become infected with the tapeworm when they ingest infected animal tissue that contains cysticerci
  • note, ingestion of cysticerci lead to the formation of tapeworms that reside in the proximal small bowel (e.g., Taenia solium and T. saginata) vs ingestion of eggs passed in human or animal feces leads to the formation of oncospheres, causing extraintestinal cystic lesions (e.g., T. solium and Echinococcus)