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Chapter: Medical Microbiology: An Introduction to Infectious Diseases: Trematodes

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Clonorchiasis ( Liver Fluke Infection )

Praziquantel and albendazole have proven to be effective therapeutic agents. Prevention requires thorough cooking of freshwater fish and sanitary disposal of human feces.

CLONORCHIASIS ( LIVER FLUKE INFECTION )

EPIDEMIOLOGY

Clonorchiasis is endemic in the Far East, particularly in Korea, Japan, Taiwan, the RedRiver Valley of Vietnam, the Southern Chinese province of Kwantung, and Hong Kong. In previous years, parasite transmission was perpetuated by the practice of fertilizing commercial fish ponds with human feces. Recent improvements in the disposal of human waste have diminished acquisition of the disease in most countries. However, the extremely long lifespan of these worms is reflected in a much slower decrease in the over-all infection rate. In some villages in southern China, the entire adult population is in-fected. A recent survey of stool specimens from immigrants from Hong Kong to Canada showed an infection rate of more than 15% overall and 23% in adults between 30 and 50 years of age. The disease is acquired by eating raw, frozen, dried, salted, smoked, or pickled fish. Commercial shipment of such products outside of the endemic area may result in the acquisition of worms far from their original source.

 MANIFESTATIONS

Migration of the larvae from the duodenum to the bile duct may produce fever, chills, mild jaundice, eosinophilia, and liver enlargement. The adult worm induces epithelial hy-perplasia, adenoma formation, and inflammation and fibrosis around the smaller bile ducts. In light infection, clinical disease seldom results. However, numerous reinfections may produce worm loads of 500 to 1000, resulting in the formation of bile stones and sometimes bile duct carcinoma in patients with severe, long-standing infections. Calculus formation is often accompanied by asymptomatic biliary carriage of Salmonella typhi. Dead worms may obstruct the common bile duct and induce secondary bacterial cholan-gitis, which may be accompanied by bacteremia, endotoxin shock, and hypoglycemia. Occasionally, adult worms are found in the pancreatic ducts, where they can produce duc-tal obstruction and acute pancreatitis.

DIAGNOSIS

Definitive diagnosis requires the recovery and identification of the distinctive egg from the stool or duodenal aspirates. In mild infections, repeated examinations may be re-quired. Because most patients are asymptomatic, any individual with clinical manifesta-tions of disease in whom Clonorchis eggs are found must be evaluated for the presence of other causes of illness. In acute symptomatic clonorchiasis, there is usually leukocytosis, eosinophilia, elevation of alkaline phosphatase levels, and abnormal computed tomogra-phy and ultrasonographic liver scans. Cholangiograms may reveal dilatation of the intra-hepatic ducts, small filling defects compatible with the presence of adult worms, and occasionally cholangiocarcinoma.

TREATMENT AND PREVENTION

 

Praziquantel and albendazole have proven to be effective therapeutic agents. Prevention requires thorough cooking of freshwater fish and sanitary disposal of human feces.

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