STEPTRACKERMICROBIOLOGY + PATHOLOGY | CESTODES, TREMATODES & VECTORS | HIGH-YIELD REVIEW

Cestodes, Trematodes & Vectors

Tapeworms and flukes — what you swallow decides whether you get a gut worm or cysts in the brain and liver — plus the arthropods that carry disease.

FOCUS ON
Taenia solium: undercooked pork with larvae → intestinal tapeworm; ingesting eggs (fecal-oral) → cysticercosis/neurocysticercosis (cystic brain lesions, seizures) → albendazole (+ steroids), praziquantel for gut worm. Diphyllobothrium: raw fish → B12 deficiency. Echinococcus granulosus: dog feces (sheep areas) → hydatid liver cyst ("eggshell" calcification); spillage → anaphylaxis → albendazole + careful surgery (PAIR). Schistosoma: freshwater snails, skin penetration → S mansoni/japonicum (portal hypertension), S haematobium (hematuria, squamous cell bladder cancer) → praziquantel. Clonorchis: raw fish → cholangiocarcinoma. Paragonimus: crabs → hemoptysis.
PARASITE
SOURCE · ROUTE
DISEASE
CLUE · TREATMENT
Taenia solium — taeniasis
Undercooked pork containing cysticerci (larvae)
Adult tapeworm in gut, mild symptoms, proglottids in stool
Praziquantel
Taenia solium — neurocysticercosis
Swallowing eggs from a human carrier (fecal-oral) — no pork needed
New-onset seizures, headache, hydrocephalus; multiple cysts with scolex ("cyst with a dot"), calcifications
Most common cause of adult seizures worldwide · albendazole + steroids, antiseizure drugs
Taenia saginata
Undercooked beef
Intestinal tapeworm only (no cysticercosis)
Praziquantel
Diphyllobothrium latum
Raw or undercooked freshwater fish (sushi, ceviche)
Longest tapeworm; competes for B12 → megaloblastic anemia, neuropathy
Praziquantel + B12
Echinococcus granulosus
Eggs from dog feces; dogs eat sheep offal (sheep-raising regions)
Slow-growing hydatid cyst in liver (right lobe) or lung with daughter cysts
"Eggshell" calcification · rupture → anaphylaxis · albendazole + PAIR or surgery (with scolicidal agent)
Echinococcus multilocularis
Foxes, rodents (northern hemisphere)
Infiltrative "alveolar" liver lesions mimicking cancer
Surgery + albendazole
Schistosoma mansoni · japonicum
Cercariae from freshwater snails penetrate skin; adults in mesenteric veins
Swimmer's itch → Katayama fever → egg granulomas in liver → pre-sinusoidal portal hypertension, "pipestem" fibrosis, varices, splenomegaly
Eggs with lateral (mansoni) spine · praziquantel
Schistosoma haematobium
Same route; adults in bladder venous plexus (Africa, Middle East)
Terminal hematuria, bladder fibrosis/calcification, hydronephrosis → squamous cell carcinoma of bladder
Eggs with terminal spine in urine · praziquantel
Clonorchis sinensis · Opisthorchis
Raw freshwater fish (East Asia)
Biliary inflammation, pigmented stones, cholangiocarcinoma
Praziquantel
Paragonimus westermani
Undercooked crabs/crayfish (Asia)
Chronic cough, hemoptysis, mimics TB
Praziquantel
Fasciola hepatica
Watercress contaminated by sheep/cattle
RUQ pain, biliary obstruction, eosinophilia
Triclabendazole

Mechanism — larva vs egg in Taenia solium

Eat pork with larvae
→
Adult worm in intestineTaeniasis
Swallow eggsFecal-oral from a carrier
→
Larvae penetrate gut → blood
→
Cysts in brain, muscle, eyeCysticercosis

Arthropod vectors

VECTOR
DISEASES
REGION
Ixodes tick
Lyme, babesiosis, anaplasmosis
Northeast, upper Midwest US
Dermacentor tick
RMSF, tularemia
Southeast/south-central US
Amblyomma tick
Ehrlichiosis; alpha-gal allergy
Southeast US
Louse
Epidemic typhus, trench fever, relapsing fever
Crowding, homelessness
Flea
Plague, endemic typhus
Rodents
Mosquito
Malaria, dengue, Zika, West Nile, filariasis
Tropics, US summer

How it's tested

COMMON CONFUSIONNeurocysticercosis needs eggs from a human carrier, not pork — a vegetarian can get it from a household member with taeniasis.
THE TRAPAspirating a hydatid cyst without precautions risks anaphylaxis and seeding — albendazole and scolicidal protocols come first.
YOUR APPROACHWhat was eaten or touched (pork, fish, dog, freshwater, crab) → worm → organ → praziquantel for flukes and gut tapeworms, albendazole for tissue cysts.

If you see… think…

Immigrant with new seizures and multiple brain cysts with a dot → neurocysticercosis
Megaloblastic anemia in a fan of raw freshwater fish → Diphyllobothrium latum
Sheep farmer with a calcified liver cyst → Echinococcus granulosus
Anaphylaxis during liver cyst surgery → hydatid cyst spillage
Egyptian man with hematuria and bladder cancer → Schistosoma haematobium (squamous)
Portal hypertension with normal liver function after African lakes → S mansoni
Cholangiocarcinoma in a man from Southeast Asia → Clonorchis/Opisthorchis
Hemoptysis after eating raw crabs → Paragonimus
Drug for most flukes and adult tapeworms → praziquantel
Tick linked to Lyme and babesiosis → Ixodes