288 - Trematodes (Schistosomes and Liver, Intestinal, and Lung Flukes)

Abstract

Schistosomes and the nonschistosomal foodborne trematodes are highly prevalent flatworms that infect people throughout the world, particularly in resource-limited settings. Schistosomiasis is acquired by contact with fresh water infested by the intermediate snail host. Previously uninfected persons may develop acute infection with fever and eosinophilia on first exposure, whereas chronically infected persons are at risk for disease of the intestines, liver, or genitourinary tract caused by the inflammatory reaction to eggs shed by the adult worms that live in blood vessels. Diagnosis is by microscopic identification of eggs, serology, detection of circulating antigens, or polymerase chain reaction. All persons with schistosomiasis should be treated with praziquantel, including asymptomatic persons with light infections, because they are at risk for serious neurologic complications from the ectopic deposition of eggs. The foodborne trematodes include the liver flukes (Clonorchis, Opisthorchis, and Fasciola), numerous species of intestinal flukes, and the lung fluke (Paragonimus). Although snails are the first intermediate host, these infections are acquired by ingestion of poorly cooked or uncooked fish, crustaceans, or aquatic vegetation, the second intermediate hosts. Some persons will present with fever and eosinophilia during the early stages of infection. Complications of heavy chronic infections include biliary disease, chronic diarrhea, or cystic pulmonary or brain lesions, depending on the species. Praziquantel is the treatment of choice for all species except for Fasciola, which is best treated with triclabendazole. Global control efforts for control of trematode infections include mass drug administration to populations at risk, provision of sanitation and clean water, and food safety.