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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)
      •  
 
Tapeworms (Cestodes)
Organism
Clinical Manifestation(s)
Transmission Treatment
Taenia solium ("pork tapeworm")
  • Intestinal tapeworm
    • most carriers are asymptomatic
    • passage of proglottids in stool
    • may have nausea, anorexia, or epigastric pain
    • peripheral eosinophilia may be seen
  • Cysticercosis
    • most commonly affecting muscles or subcutaneous tissues
  • Neurocysticercosis 
    • seizures (most common clinical manifestation with involvement of the brain parenchyma)
    • headache
    • altered mental status
  • Consumption of
    • larvae in undercooked pork (intestinal tapeworm)
    • eggs in foods contaminated in human feces (cysticercosis and neurocysticercosis)

  • Albendazole or albendazole and praziquantel (for neurocysticercosis)
Taenia saginata ("beef tapeworm")
  • Intestinal tapeworm
    • most carriers are asymptomatic
    • passage of proglottids in stool
    • may have nausea, anorexia, or epigastric pain
    • peripheral eosinophilia may be seen
  • Consumption of undercooked beef
  • Praziquantel
Diphyllobothrium latum ("fish tapeworm")
  • Vitamin B12 deficiency 
    • leads to development of megaloblastic anemia
  • Consumption of larvae in raw freshwater fish
  • Praziquantel
Echinococcus granulosus
  • Liver hydatid cysts 
    • typically patients are asymptomatic
    • right hepatic lobe is most commonly affected
    • when the cyst is large, patients can present with hepatomegaly and right upper quadrant pain
    • cysts can rupture in the
      • peritoneum, leading to peritonitis
      • pleural space, leading to pulmonary hydatidosis
      • biliary tree, leading to biliary colic, obstructive jaundice, cholangitis, or pancreatitis
  • Consumption of eggs in foods that are contaminated in dog feces
  • Sheep are an intermediate host
  • Albendazole
 
 

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(M1.MC.13.115) A 35-year-old shepherd is found to have a large hydatid cyst in his liver. His doctor explains to him that surgery is required to remove the cyst, as aspiration of the contents would risk an anaphylactic reaction in the patient. What is the most likely cause of this patient's cyst? Tested Concept

QID: 101172
1

Diphyllobothrium latum

7%

(23/344)

2

Echinococcus granulosus

67%

(231/344)

3

Taenia solium

8%

(28/344)

4

Schistosoma

10%

(35/344)

5

Clonorchis sinensis

7%

(24/344)

L 2 E

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