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Overview: Trematodes (flukes) are members of the phylum Platyhelminthes (flatworms); they are flat, fleshy, leaf shaped worms. Shistosomes are an exception, as they have cylindrical bodies. All flukes require a mollusk (e.g. clam, snail) intermediate host. Fluke eggs have a lid, called an operculum, that opens to allow the larval worm to find its mollusk host. Of note, shistosomes don't have an operculum, the eggs just split open. All flukes are hermaphroditic, except shistosomes.

Fasciolopsis buski
- giant intestinal fluke
- intestinal fluke found in SE Asia
- Transmission: snail serves as intermediate host. Free swimming organisms (Cercaria) are released from the snail and attach to water plants. Human ingests the water chestnut and gets infected.
- Vector: Water plants (e.g. water chestnuts)
- Clinical: abd pain, diarrhea, bowel obstruction, marked eosinophilia
- Dx: stool O&P shows bile-stained eggs w/ operculum
- Tx: Praziquantel
Fasciola hepatica
- Sheep liver fluke
- Reservoir: humans, sheep, cattle
- Intermediate host: snail
- Vector: Water plants (watercress, water chestnuts)
- Larval flukes migrate through duodenal wall and across peritoneal vacity, penetrate the liver capsule, and enter the bile ducts. There, they become adult worms. 3-4 months after ingestion, the adult worms starts producing operculated eggs.
- Clinical: RUQ pain, hepatomegaly, fevers, chills, eosinophilia. May get areas of liver necrosis. May get hepatic bacterial superinfection or cirrhosis.
- Dx: O&P, may see operculated eggs (indistinguishable from F. buski). Can examine bile; if eggs are in bile, then it is F. hepatica and not F. buski. CT liver shows peripheral, tunnel like branching hypodense lesions. Check serology.
- Tx: Triclabendazole (preferred) or Bithionol (*note: responds poorly to praziquantel)
Opisthorchis sinensis
- Small liver fluke, Chinese Liver Fluke
- Vector: uncooked fish
- Intermediate host: snail, freshwater fish
- Reservoir: humans, dogs, cats
- Epi: China, Japan, Korea, Vietnam
- Clinical: usually mild and asymptomatic infx. Severe infx: fever, diarrhea, epigastric pain, hepatomegaly, anorexia, jaundice, biliary obstruction. Chronic infx: recurrent cholangitis and cholangiocarcinoma, liver abscess.
- Dx: O&P shows eggs w/ distinct operculum (prominent shoulders and tiny know at the posterior pole). Imaging may show abnormalities of the biliary tract.
- Prevention: avoid uncooked fish
- Tx: Praziquantel
Paragonimus westermani
- Lung fluke
- Intermediate host: snail, freshwater crabs, crayfish
- Vector: uncooked crabs, crayfish
- Reservoir: humans, pigs, monkeys
- Transmission: ingestion of infected crab or crayfish, larval worm hatches in the stomach and migrates through the intestinal wall to the abdominal cavity, then through the diaphragm, and finall to the pleural cavity. Adult worms reside in the lungs and produce eggs there. The eggs may appear in the sputum, and if swallowed, in the feces as well.
- Epi: Asia, Africa, India, Latin America
- Easily confused with: pulmonary TB
- - think of patient with TB like presentation who does not improve following treatment for TB
- Clinical: fevers, chills, eosinophilia, cough, productive of sputum, cavitary lung lesion, hemoptysis/rusty sputum, chest pain. May see dyspnea, chronic bronchitis, bronchiectasis, pleural effusions, pulmonary fibrosis, extra-pulmonary involvement: spinal cord, brain (cerebral paragonimiasis)), abdomen, liver.
- Dx: O&P shows golden brown operculated eggs. Examine any pleural effusion for eggs. CXR w/ infiltrates, nodular cysts / cavitary lesion, pleural effusion. Check serology.
- Prevention: avoid uncooked crabs and crayfish
- Tx: Triclabendazole (alternative: praziquantel)
Schistosomes
- Schistosoma mansoni
- Schistosoma japonicum
- Schistomsoma haematobium
Cercarial Dermatitis