Biliary liver flukes (opisthorchiasis and clonorchiasis) in immigrants in the United States: Often subtle and diagnosed years after arrival

Background: Biliary liver flukes are extremely common parasites in some regions of the world where consumption of raw fresh-water fish is a cultural practice. Clonorchis sinensis and Opisthorchis spp. are the major biliary liver flukes associated with human disease. Some of these parasites are highly associated with cholangiocarcinoma. It was noted that several cases presenting at our center had been in the US for prolonged periods. This prompted us to retrospectively review cases of liver fluke infection diagnosed at our facility. Methods: All cases of biliary liver fluke infection over a 6-year period were retrospectively investigated at a clinic serving international patients, to determine the prevalence and risk factors for infection in a nonendemic area. Cases were identified through review of stool ova and parasite (O&P) records maintained at Regions Hospital/HealthPartners microbiology laboratory. All O&P samples positive for Opisthorchis spp. or Clonorchis sinensis were included in the review. Results: Seventeen cases were identified during the study period. Our center performed approximately 1,800 stool O&P examinations per year on approximately 1,100 individuals per year during the study period. Biliary liver flukes were uncommon, accounting for 1.3% of individuals infected with organisms considered to be potentially pathogenic. Infections were predominantly found in migrants from Laos, Cambodia and Thailand. Cases were also identified in migrants from the former Soviet Union and South America. It is of note that 25% of patients were detected after 5 years of residence in the US. Often, the only clinical clue to infection was a mild absolute eosinophilia (500 to 1000 μL). Conclusions: Although biliary liver fluke is an infrequent cause of infection in immigrants to the US, because of the potential long-term consequences of chronic infection, educational information highlighting routes of infection and the fact that asymptomatic infection is common and may eventually lead to cancer should be aimed at high-risk community members and those who have been visiting friends and relatives in endemic areas.