- Karin Leder, MBBS, FRACP, PhD, MPH, DTMH
Karin Leder, MBBS, FRACP, PhD, MPH, DTMH
- Section Editor — Travel Medicine
- Head of Infectious Diseases Unit
- Monash University, Australia
- Peter F Weller, MD, MACP
Peter F Weller, MD, MACP
- Editor-in-Chief — Infectious Diseases
- Section Editor — Tropical Medicine
- William Bosworth Castle Professor of Medicine
- Harvard Medical School
- Professor of Immunology and Infectious Diseases
- Harvard T. H. Chan School of Public Health
Intestinal flukes (trematodes) are flat hermaphroditic worms that range in size from a few millimeters to several centimeters. Approximately 70 trematode species have been reported to colonize the human intestinal tract. The geographic distribution is worldwide; the highest prevalences are in East and Southeast Asia. Infection in the United States can be acquired via importation as well as locally; the most common species include Nanophyetus, Alaria, and Heterophyes . Intestinal trematodes are among the commonest parasitic infections in humans and animals but are less associated with mortality than many other parasites . Sources for transmission of human infection include fish, crustaceans, and aquatic plants, and endemicity of infection is associated with cultural and eating habits.
Four of the most frequently described intestinal flukes will be reviewed here: Fasciolopsis buski, Heterophyes heterophyes, Metagonimus yokogawai, and Echinostoma species.
Issues related to liver flukes are discussed separately. (See "Liver flukes: Clonorchis, Opisthorchis, and Metorchis" and "Liver flukes: Fascioliasis".)
F. buski is the largest intestinal fluke of humans; pigs are also mammalian hosts. The infection is common in Southeast Asia and the Far East, especially in areas where humans raise pigs and consume freshwater plants.
The life cycle begins with release of immature eggs in mammalian stool (figure 1). These eggs become embryonated in water and release miracidia, which enter snail intermediate hosts. In the snail, the parasites undergo several developmental stages (sporocysts, rediae, and cercariae). The cercariae are released from the snail and encyst as metacercariae on aquatic plants, where they can survive for prolonged periods (often up to a year). Mammalian hosts become infected by ingesting metacercariae on the aquatic plants. After ingestion, the metacercariae excyst in the duodenum and attach to the intestinal wall, where they develop into adult flukes in approximately three months. Adult worms are 2 to 7.5 cm long and 1 to 2 cm wide; they have a lifespan of about one year and produce approximately 25,000 eggs daily .
- Fried B, Abruzzi A. Food-borne trematode infections of humans in the United States of America. Parasitol Res 2010; 106:1263.
- Hung NM, Madsen H, Fried B. Global status of fish-borne zoonotic trematodiasis in humans. Acta Parasitol 2013; 58:231.
- Liu LX, Harinasuta KT. Liver and intestinal flukes. Gastroenterol Clin North Am 1996; 25:627.
- Sripa B, Kaewkes S, Intapan PM, et al. Food-borne trematodiases in Southeast Asia epidemiology, pathology, clinical manifestation and control. Adv Parasitol 2010; 72:305.
- Singh UC, Kumar A, Srivastava A, et al. Small bowel stricture and perforation: an unusual presentation of Fasciolopsis buski. Trop Gastroenterol 2011; 32:320.
- Keiser J, Utzinger J. Food-borne trematodiases. Clin Microbiol Rev 2009; 22:466.
- Bunnag D, Radomyos P, Harinasuta T. Field trial on the treatment of fasciolopsiasis with praziquantel. Southeast Asian J Trop Med Public Health 1983; 14:216.
- World Health Organizaiton Model Prescribing Information: Drugs Used in Parasitic Diseases - Second Edition: Helminths http://apps.who.int/medicinedocs/es/d/Jh2922e/3.8.1.html#Jh2922e.3.8.1 (Accessed on September 11, 2015).
- Drugs for Parasitic Infections, 3rd Ed, The Medical Letter, New Rochelle, NY 2013.
- Chai JY, Lee SH. Food-borne intestinal trematode infections in the Republic of Korea. Parasitol Int 2002; 51:129.
- Chai JY, Song TE, Han ET, et al. Two endemic foci of heterophyids and other intestinal fluke infections in southern and western coastal areas in Korea. Korean J Parasitol 1998; 36:155.
- Belizario VY Jr, Bersabe MJ, de Leon WU, et al. Intestinal heterophyidiasis: an emerging food-borne parasitic zoonosis in southern Philippines. Southeast Asian J Trop Med Public Health 2001; 32 Suppl 2:36.
- Mahanty S, Maclean JD, Cross JH. Liver, Lung, and Intestinal Fluke Infections. In: Tropical Infectious Diseases: Principles, Pathogens and Practice, 3rd ed, Guerrant RL, Walker DH, Weller PF (Eds), Saunders Elsevier, Philadelphia 2011. p.854.
- Jeon HK, Lee D, Park H, et al. Human infections with liver and minute intestinal flukes in Guangxi, China: analysis by DNA sequencing, ultrasonography, and immunoaffinity chromatography. Korean J Parasitol 2012; 50:391.
- Pungpak S, Radomyos P, Radomyos BE, et al. Treatment of Opisthorchis viverrini and intestinal fluke infections with Praziquantel. Southeast Asian J Trop Med Public Health 1998; 29:246.
- Toledo R, Esteban JG. An update on human echinostomiasis. Trans R Soc Trop Med Hyg 2016; 110:37.
- Carney WP. Echinostomiasis--a snail-borne intestinal trematode zoonosis. Southeast Asian J Trop Med Public Health 1991; 22 Suppl:206.
- Pungpark S, Bunnag D, Harinasuta T. Albendazole in the treatment of opisthorchiasis and concomitant intestinal helminthic infections. Southeast Asian J Trop Med Public Health 1984; 15:44.
- Wiwanitkit V, Nithiuthai S, Suwansaksri J. Motility of minute intestinal fluke, Haplorchinae spp, metacercariae in fish dishes prepared by different uncooked methods. MedGenMed 2002; 4:8.