Fasciola hepatica infects sheep, goats and cattle, in which it produces liver disease, and is only accidentally transmitted to humans via consumption of wild watercress grown on the grazing land of infected animals. The disease is found worldwide, including the UK. Animals excrete eggs in their faeces, from which ciliated miracidia emerge. These enter the freshwater snail (the intermediate host) in which larval development takes place. Eventually cercaria are released and these encyst on aquatic or surface vegetation.
After ingestion by a mammalian host, the parasites excyst, migrate through the intestinal wall and penetrate the liver capsule after traversing the peritoneal cavity. Immature flukes reach the bile duct by passing through liver parenchyma and after maturation begin to produce eggs. Adult flukes remain within the biliary tract for many years.
Early symptoms of intermittent fever, malaise, weight loss, right upper quadrant pain and urticaria relate to migration of flukes through the liver and generally occur 2-3 months after infection. A second phase of the illness relates to the presence of ukes in the biliary tract, where they can cause obstrucn with jaundice and cholangitis, although infection y remain asymptomatic. Flukes have been found in y ectopic sites, including lung, brain and skin.
Eosinophilia is common in the early phase of the illness d is often associated with liver biochemical abnormalies and a positive complement fixation test. Ova are notd in the stool until the second phase of the illness en the mature flukes are established in the biliary tract. Ho “ever, in up to 30% of cases, stools remain negative; e diagnosis can then be confirmed either by identifying “3 in duodenal aspirate or by serological tests. Treatt is with bithionol 30-50 mg kg'” for 10-15 doses either daily or on alternate days.
Cnorchis sinensis is a common fluke of the dog, cat and pig that affects millions of animals in the Far East, pararly Indo-China, Japan, Korea, Hong Kong and Vietnam. A related fluke, Opisthorchis felineus, also affects foxes and is found predominantly in India, the Philipines Korea and Japan. The life-cycles of both these flukes are similar to that of F. hepatica, except that freshwater fish become infected by the cercaria and thereby function as a second intermediate host. Human infection occurs by ingestion of infected raw fish.
Infected individuals may remain symptom-free, although prolonged exposure with heavy infection results in recurrent cholestatic jaundice, suppurative cholangitis, liver abscess and cholangiocarcinoma.
The diagnosis is made on microscopic examination of faeces or duodenal aspirate.
Praziquantel 25 mg kg” as a single dose is the treatment of choice.
Fasciolopsis buski causes intestinal infection in humans and pigs. There are two intermediate hosts-freshwater snails and water plants. Human infection is initiated by oral contact with contaminated water plants. These large flukes, which are several centimetres in length, are common in China, Vietnam, Thailand and Taiwan. Mucosal ulceration and inflammation are apparent at the site of attachment in the intestine; abscess formation, haemorrhage and occasionally bowel obstruction may result. The symptoms are usually non-specific. Heavy infection in children may simulate or precipitate proteinenergy malnutrition. Anaemia and eosinophilia are common.
The diagnosis may be simple if the patient is vomiting or passing flukes per rectum, but may be confirmed by identifying ova in the stools.
Treatment is with tetrachloroethylene 0.12 ml kg:’ as a single dose (maximum dose of 5 ml) or dichlorophen 100 mg kg-l as a single dose (which may be repeated 1 week later).