BMS655 Liver flukes

Fasciola hepatica

Sheep liver fluke

infects liver of cattle and sheep

infections in humans after consuming raw contaminated aquatic vegetables

Morphology

Monoecious

Leaf-shaped flat worm

Tegument covered with large, scale like spines

Definitive host

mammals

Intermediate host

mud snails

Definitive host propagule

Metacercariae

Intermediate host propagule

Miracidium

Egg production and fertilization

Adults are hermaphroditic, capable of both cross- and self-fertilization (self occurs rarely)

Egg development

Eggs shed in feces into water hatch after 10 days into miracidium

Can only survive for about 24 hours

Egg hatching

Stimulated by blue-violet light

Operculum pops open to release miracidium

Transmission to snails

Miracidium burrows into snail, transforms to sporocysts

Sporocysts produce rediae, multiply to produce cercariae

Cercariae emerge from snail 5-7 days after infection

Cercariae drop tails and produce thick cyst wall to become metacercariae in water

Transmission to mammals

Infected after ingesting metacercariae

Excyst in small intestine releasing juvenile fluke

Juvenile penetrates intestinal wall, creep around until reach the liver

Fluke burrows into liver, eventually reach the bile duct

Become sexually mature after 1 month, start producing eggs

How does the fluke find the liver

Molecular signposts (bile salt)

Independent of brain function (cerebral ganglion not fully developed)

Pathology

Movement of liver causes necrosis

Worms feed on liver cells and blood (may cause anaemia)

Worms in bile ducts cause inflammation

Atrophy of liver tissue (cirrhosis, jaundice)

Damage of bile duct and worms entering parenchyma causing abscesses

Can end up in CNS or ocular tissue

Early (acute) phase symptoms

Mild symptoms can occur during migration from intestines to liver

Gastrointestnial probles such as nausea, vomiting, and abdominal pain

Starts a few days after exposure, can last several weeks or months

Chronic phase (parasite in bile duct)

Inflammation and blockage of bile ducts

Fever, malaise, abdominal pain, eosinophilia, hepatomegaly, abnormal liver function

Inflammation of gallbladder and pancreas

Diagnosis

Eggs detected during chronic phase of infection

Adult flukes detected with endoscopic retrograde cholangiopancreatography

Treatment

Triclabendazole

Prevention in humans

Wash aquatic vegetables before eating

Prevention in livestock

Snail control

Vaccine development

Fasciola gigantica

Common in herbivorous mammals, particularly cattle

Different snail host to F. hepatica

Other liver flukes

Clonorchis sinensis - Chinese liver fluke

Opisthorchis - Opisthorchiasis

C. sinensis

Asia

Consuming contaminated raw fish

Adults reside in bile duct, eggs passed in feces

Apisthorchis

Asia and Europe

Contaminated raw fish

Adult worms in bile duct, eggs passed in feces

Flukes and cancer

Schistosoma haematobium (blood fluke) associated with bladder cancer

O. viverrini (liver fluke) associated with cholangiocarcinoma (bile duct cancer)