2The lancet liver fluke (0.5–1.0 ! 0.2 cm) Fasciola hepatica F. hepatica is a flattened,leaf-shaped parasite about2–5 cm long and at most1 cm wide.Dicrocoelium dendriticumThe lancet liver fluke(0.5–1.0 ! 0.2 cm)Fasciola hepatica and F. gigantica are bile duct parasites of domestic ruminants.In their life cycle freshwater snails act as intermediate host Humans become accidentally infected when they eat plants to which infectious parasite stages (metacercariae) adhere Dicrocoelium dendriticum is a bile duct parasite in sheep, cattle, and other herbivores, Its life cycle includes two intermediate hosts (terrestrial snails and ants). Humans become infected accidentally when they ingest ants containing infective metacercariae of the lancet liver fluke.
5Life cycle of Fasciola hepatica Adult liver flukes parasitize in the bile ducts. They produce large golden brown, operculated eggs that are shed by the bile duct-intestinal tract route. Under favorable conditions, a ciliate larva, the miracidium, develops in the egg within a few weeks. The miracidia then hatch and penetrate into freshwater snails where they transform into sporocysts.
6Life cycle of Fasciola hepatica After formation of further asexual reproductivestages, tailed cercariae develop and swarm outof the snails into the open water.They soon attach to plants and encyst, transforminto infective metacercariae, which are theningested with vegetable food of their definitivehosts.Eating watercress contaminated with metacercariaeis one of the sources of infection for humans.
7Life cycle of Fasciola hepatica The juvenile liver flukes hatch from the cyst in thesmall intestine, penetrate the intestinal wall, andmigrate through the peritoneal cavity to the liver.After migrating through the hepatic parenchymafor about six to seven weeks, the parasites finallyreach the bile ducts, in which they developto sexual maturity.Egg excretion begins two to three months
8Life cycle of Dicrocoelium dendriticum It stands apart from most trematodes since it has a landbased life cycle. The definitive host's feces containmiracidia which do not hatch until after they are eaten bythe first intermediate host, a land snail,The miracidium emerges inside the intestine of the snailand metamorphoses into a sporocyst and than intocercaria.The second intermediate host is the common brown ant,There cercaria turns to metacercaria.Upon ingestion by the definitive host, the metacercariaarrive in the duodenum and migrate up the common bileduct to the liver. The adult fluke matures in 6-7 weeks,producing egg capsules about a month later.
10Dicrocoelium dendriticum Fasciola hepatica Eating watercress contaminated with metacercariae is one of the sources of infection for humans.Dicrocoelium dendriticumHumans become infected accidentally when they ingestants containing infective metacercariae of the lancet liverfluke.Such infections are rare and either run an asymptomaticcourse or manifest in mild abdominal and hepaticsymptoms.
12Diagnosis of Fasciola infection Diagnosis of Fasciola infection . The manifestations to be expected during the migration phase of the liver fluke include mainly leukocytosis, eosinophilia, and a rise in liverspecific serum enzymes. Detection of eggs in stool or duodenal fluid is not possible until at least two to three months . Other diagnostic tools include detection of serum antibodies and of coproantigen in stool.Diagnosis of Dicrocoelium infection. Diagnosis is basedon detection of eggs in stool (about µm, oval, darkbrown containing a miracidium with two rounded germinalcells) Ingestion of contamined beef or mutton liver canresult in egg excretion in stool without infection.This isintestinal passage.
13Praziquantel has been shown to be effective Treatment of Fasciola infection The drug of choice is triclabendazole, the infection can be avoided by not eating raw watercress and other plants that may be contaminated with metacercariae.Treatment of Dicrocoelium infectionPraziquantel has been shown to be effectiveagainst Dicrocoelium in animals .
15Clonorchis spp Liver flukes of the genera Clonorchis occur mainly in river and lake regions of Asia and Eastern Europe.The definitive hosts of Clonorchis species are fisheating mammals like cats,dogs, pigs, and humans,inwhich these trematodes colonize the bile ducts.
17Clonorchis spp The life cycle of these organisms involves various species of aquatic snails as the first intermediatehosts and freshwaterfish species as the secondintermediate hosts.The infective metacercariae are localized in themusculature of the fish and,when raw fish isingested, enter the intestinal tract of the definitivehost, they migrate through the common bile duct
20Clonorchis spp Pathogenesis and clinical manifestations. Clonorchis infections cause proliferations of the bile duct epithelium,cystlike dilatation, inflammation,and fibrosis of the bile duct walls aswell as connective tissue proliferation in the hepatic parenchyma.A high incidence of bile duct carcinomas has been reported from areasin which C. sinensis are endemic.Clinical symptoms of more severe infections include variable fever,hepatocholangitic symptoms with hepatomegaly, leukocytosis, upperpains, and diarrhea.
21Clonorchis spp Diagnosis, therapy, and prevention Diagnosis is made by detection of eggs (26–32 lm long) in stool or duodenal fluidTherapy and preventionThe drug of choice is praziquantel; albendazole can also beused.Reliable preventive measures include boiling or frying fishto kill the metacercariae, which die at temperatures aslowas 70 C, and freezing to –10 8C for five days.
22Paragonimus sp (Lung Flukes) Lung flukes of the genus Paragonimus are endemic inparts of Asia, Africa, and America.Parasitize in pulmonary cysts and cause atuberculosis-like clinical picture.Following development in two intermediatehosts(freshwater snailsband crabs or crayfish),infective stages (metacercariae) can be transmitted tohumans by eating the crabs or crayfish uncooked.Parasite eggs are detectable in sputum or stool.
23Paragonimus sp (Lung Flukes) The sexually mature parasites live in cystlikedilatations in the lungs,usually in connectionwith the bronchial tree.The yellow-brown, operculated eggs laid bythe adultworms are shed either in sputum orstool.
25Paragonimus sp (Lung Flukes) The life cycle then continues in water,where a miracidium develops in each egg,hatches and invades an intermediatebhost.Egg-shaped cercariae with short tails developin the first intermediate host, a freshwatersnail.The cercariae encyst in the second intermediatehost like crayfish or crabs to form the infectiveMetacercariae.
27Paragonimus sp When a suitable definitive host ingests the crustaceans uncooked, the young trematodeshatch in the small intestine,migrate through theperitoneal cavity to the diaphragm and finally intothe lungs.The prepatent period is two to three months.Parasites that deviate from the normal migrationroute may enter other organs.
28Paragonimus sp Besides humans, crustacean eating mammals play a significant epidemiological role as reservoirhosts.Young lung flukes can be localized in themusculature of pigs and other “transport hosts” andbe transmitted to humans who ingest the raw meatof these animals.
29Paragonimus sp Clinical manifestations. Typical cases are clinically characterized by pulmonary symptomschronic cough, bloody expectoration, thoracic pain.Parasites following the normal or deviant migrationroutes can also cause abdominal,hepatic,pancreatic or CNS symptoms, or skin lesions likeswelling, nodules.
30Paragonimus sp Diagnosis, therapy, and prevention. An etiological diagnosis is based on detection of eggs insputum or stool and of serum antibodies.Regarding the differential diagnosis especially tuberculosismust be kept in mind.The drug of choice is praziquantel, but triclabendazolemcan also be used .Cooking crustaceans before eating them is a reliablepreventive measure.