Common-source outbreak of acute infection due to the North American liver fluke Metorchis conjunctus

Background We investigated an outbreak of acute clinical illness among 19 people who ate raw fish (sashimi) prepared from the white sucker, Catostomus commersoni, caught in a river north of Montreal, Canada. Methods We collected epidemiological, clinical, laboratory, and serological data on 19 individuals who ate the sashimi and six who did not. Because of the suggestive clinical picture, we set out to recover helminth parasites from uneaten fish. Findings The illness consisted of persistent upper abdominal pain, low grade fever, high blood eosinophil concentrations, and raised liver enzymes. After 10 days, opisthorchiid-like eggs were found in stools. Symptoms persisted for 3 days to 4 weeks without treatment, but responded rapidly to praziquantel therapy. Necropsy of golden hamsters infected with metacercariae from uneaten fish revealed adult flukes identified as Metorchis conjunctus. Interpretation We describe an acute illness caused by the North American liver fluke M conjunctus. This is a new human disease and is the first report of a common-source outbreak of an acute illness caused by liver flukes of the family Opisthorchiidae.