Metorchis conjunctus is in the same family as Opisthorchis and Clonorchis species but is only found in North America, where it normally infects wild carnivores and has been noted as a cause of death of sled dogs (Table 17.1). Human infection occurs rarely. Recently, an outbreak of acute illness caused by M. conjunctus was described in 19 people who ate raw fish near Montreal, Canada (MacLean et al., 1996). Many of the individuals had abdominal pain, fever, headache, weight loss and fatigue after an incubation period of 1-15 days. In addition, eosinophilia and elevated liver enzyme concen trations were noted in the majority of those infected. The symptoms lasted for 3 days to 4 weeks, with rapid resolution after treatment with praziquantel. Besides this description of acute illness, there is little information on infection attributed to M. conjunctus. While the eggs have been detected in asymptomatic individuals, there is no known association of this parasite with chronic clinical features such as cholangitis or cholangiocarcinoma associated with other hepatobiliary flukes.
Dicrocoelium species have also rarely been associated with human infection. Dicrocoelium dendriticum is found in Europe, North and South America, Africa and Saudi Arabia, while D. hospes is present in Africa. Infections are acquired by ingesting metacercariae from ants, which serve as the second intermediate host (Mohamed and Mummery, 1990). Humans can also acquire a pseudoinfection by ingesting adult worms in raw or undercooked liver from infected mammals. In a series of 208 individuals from Saudi Arabia, 81%
had symptoms, which most often included abdominal pain. In addition, liver enzyme concentration elevations, eosinophilia and gall bladder abnormalities on ultrasound were noted in many of the patients. There were no control groups for comparison to evaluate the specificity of the clinical features of the illness or the radiographic abnormalities. Praziquantel was successful in alleviating symptoms in four of nine individuals.
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