Foodborne trematodiases infect 40 million people worldwide, and 750 million people are at risk. Fasciolopsiasis occurs mainly in rural Southeast Asia, central and southern China, and India. Prevalence is highest in pig-farming areas. Use of pig or human feces for fertilization is associated with endemicity. Children younger than 15 years are often more commonly infected than adults due to gathering and eating contaminated water plants during play.
Fasciolopsis buski is one of the largest flukes that infects humans, with a body length of 2-7.5 cm and width of 0.8-2 cm. It mainly inhabits the duodenum and jejunum, where the flukes produce large eggs (130-159 µm by 78-98 µm) that are oval, thin shelled, and yellow. Egg opercula are inconspicuous.
Fasciolopsiasis is a disease where humans are intentional definitive hosts. Animal reservoirs include pigs and less commonly dogs. Intermediate hosts are snails. The site of infection is the small intestine (duodenum and jejunum).
Unembryonated eggs are released from adult trematodes into the intestine and stool of host mammals. Stool is excreted into fresh water, where miracidia hatch and penetrate the intermediate host, a snail of the family Planorbidae. In the snail, the trematodes multiply and develop into free-living cercariae. Cercariae emerge from the snail and attach to a variety of aquatic plants (water chestnuts, water bamboo, water caltrop, water hyacinth, lotus, etc) and encyst as metacercariae. Humans and other mammals become infected on ingestion of metacercariae attached to aquatic plants or by drinking untreated water. When humans consume raw or undercooked infected plants, the metacercariae excyst in the duodenum and attach to the intestinal wall where they can live for up to a year. The larvae develop into mature adult flukes within 3 months and produce large numbers of eggs (an estimated 10 000-25 000 eggs per worm per day).
Fasciolopsiasis is mostly subclinical, and severity of symptoms is directly associated with the burden of infection. Attached adult flukes may produce local inflammation, ulceration, hemorrhage, or abscesses. Heavy infections may lead to acute intestinal obstruction and ileus. Patients may experience fever, anorexia, abdominal pain, vomiting, alternating constipation and chronic diarrhea, anemia, malnutrition including vitamin B12 deficiency, wasting, and eosinophilia. Peripheral edema, anasarca, and ascities may result from hypersensitivity to worm metabolites, allergic reaction, or hypoalbuminemia due to malabsorption or protein-losing enteropathy. Symptoms may develop 1 or 2 months after exposure.
B66.5 – Fasciolopsiasis
54266002 – Infection by Fasciolopsis buski
Heterophyiasis and metagonimiasis – Metacercariae encyst under the scales of fish. Infection is acquired by consumption of undercooked or salted fish. Eggs may enter a nearby lymphatic or blood vessel and may be transported to other organs where they can cause disease.
Echinostomiasis – Human infection is due to consumption of raw or incompletely cooked freshwater snails, fish, or other animals harboring metacercariae. Eggs are difficult to differentiate from those of fasciolopsiasis; however, worms recovered after chemotherapy can allow for differentiation based on morphology (circumoral disk and collar spines around the oral sucker).