Fasciolopsis

Fasciolopsis is a genus of parasitic flatworms in the class Trematoda. The best known species is Fasciolopsis buski, the giant intestinal fluke, which infects humans and pigs and can cause fasciolopsiasis. The parasite is most common in parts of South and Southeast Asia, including China, India, Vietnam, Indonesia, and the Philippines, though sporadic cases have occurred elsewhere.

Life cycle and transmission: Eggs released in feces reach fresh water and hatch into miracidia, which infect a freshwater snail as the first intermediate host. After development, cercariae leave the snail and encyst as metacercariae on aquatic vegetation. Humans and other mammals acquire infection by ingesting raw or undercooked aquatic plants bearing metacercariae. In the small intestine, metacercariae excyst and mature into adult flukes that reside mainly in the proximal small intestine and release eggs that pass in stool to continue the cycle.

Clinical features and pathology: Light infections may be asymptomatic. Heavier infections cause abdominal pain, diarrhea, anorexia, weight loss, and edema. Chronic infection can lead to malabsorption and intestinal inflammation; severe cases may cause intestinal obstruction or bleeding.

Diagnosis and treatment: Diagnosis is by detection of parasite eggs in stool, though serology or duodenal sampling can aid in certain settings. Praziquantel is the treatment of choice, typically given at 25 mg/kg three times daily for one day; alternative regimens with nitazoxanide or albendazole may be used in some cases.

Prevention: Prevention focuses on avoiding ingestion of metacercariae. This includes thorough washing and cooking of aquatic plants such as water chestnuts and water caltrops, and public health measures to reduce contamination of water with feces and to manage snail populations.