Paragonimus westermani

Paragonimus westermani egg/CDC

General Information

• There are numerous species in the genus Paragonimus that are found worldwide; primarily in Asia, but also Africa (P.africanus and P. uterobilteralis) and South America (P. peruvianus)
• P. kellicotti is found in North America
• Paragonimus westermani (most common)is also known as the "Oriental Lung Fluke".

Geography

• Found throughout Asia
• China is the major endemic area with 20 million people infected
• Also seen with low prevalence in Japan, Korea, the Philippines, Thailand

Morphology (adults)

• Large, plump flukes
• 7-16 mm length x 4-8 mm width x up to 5 mm thick
• Found in pairs in the lungs; looks like coffee beans

Morphology (eggs)

• Large, thick-shelled 
• large, flattened operculum
• 80-120 um x 50-65 um

Life Cycle

• Unembryonated eggs passed into lung tissue and excreted in sputum; or swallowed and excreted in the feces
• Eggs embryonate in the water and miracidia emerge from egg and search for specific species of snail (first intermediate host)
• In the snail, miracidia goes transforms-sporocyst> rediae> cercariae
• Cercariae leaves snail and invades second intermediate host, a crustacean, typically a crab or crayfish
• The cercariae encysts into metacercariae (infective stage for human or animal host)
• Human infected after eating inadequately cooked crustacean
• Metacercariae excysts in small intestine and penetrates the gut wall
• Peritoneal cavity> abdominal wall> diaphragm> lungs
• Develop into adults in the lungs
• Prepatent period is 2-3 months
• Infection can last for years to decades

Pathology

• Migration of young worms (acute)may produce diarrhea and abdominal pain
• When established in the lungs: Fever, cough, rusty-brown sputum, hemoptysis (often thought to be tuberculosis at first)
• Migration of worms to other organs(erratic paragonimiasis) can be very severe, particularly when brain is involved

Diagnosis

• The presence of eggs in sputum or stool.
• Serodiagnosis

Treatment

• Praziquantel is the drug of choice
• Bithionol is alternate treatment

Epidemiology

• Humans or other mammals are definitive host
• Humans get infected eating undercooked crabs or crayfish
• China- "Drunken crabs" soaked in rice wine
• Philippines- roast crabs
• Thailand- raw crayfish salad
• Korea- soak crab in soy sauce
• Use of crab juice for seasoning and medicinal purposes
• Africa- undercooked crabs for fertility
• Pickled crabs

Prevention

• Stress the importance of fully cooking crustaceans
• Proper disposal of sputum and feces

Paragonimus westermani adult/CDC

Clonorchis sinensis

Clonorchis sinensis egg  Photo/CDC

General Information

• Clonorchis sinensis is a trematode or fluke also known as the “Chinese liver fluke” or “Oriental liver fluke”
• Clonorchiasis is a trematode disease of the bile ducts
• Adult flukes produce an estimated 4,000 eggs per day per worm

Geography

• Asia only
• Mainland China, highly endemic in southeastern China
• Taiwan, Korea, Vietnam
• Reports outside of Asia are important (imported cases)

Morphology (adults)

• Slender, pointed anterior, rounded posterior
• 1-2 cm long and 3-5 mm wide
• Characteristic branching testes posterior

Morphology (eggs)

• Small, 26-30 x 15-17 um
• Ovoid, yellowish color
• Operculated at one end, small knob at opposite end

Life Cycle

• Adults in biliary ducts, embryonated eggs pass to intestine and out with the feces
• Eggs reach water, ingested by suitable snail (P. manchouricus)
• In the snail (first intermediate host, eggs release miracidium and goes through several stages in host (sporocyst>rediae>cercariae)
• Cercariae released from snail, free-swimming in water, penetrates under scales of an appropriate freshwater fish (second intermediate host)
• Metacercariae encyst in the fish muscle
• Humans infected by eating raw, partially cooked, smoked or pickled fish
• Metacercariae excysts in the duodenum
• Ascends up through intestine to bile ducts
• Matures to adult in 30 days
• Worms may live 30-40 years in final host
• Carnivorous animals can serve as reservoir hosts

Pathology

• Most infections are asymptomatic
• More progressive infections may see anorexia, jaundice, diarrhea, epigastric pain, fever
• Some infections associated with severe complications: pancreatitis, cholangitis and cholangiocarcinoma (bile duct cancer)

Diagnosis

• Finding the characteristic eggs in feces or duodenal aspirate

Treatment

• Praziquantel or albendazole are the drugs of choice

Epidemiology

• Clonorchiasis is endemic where there is poor sanitation, and
• The right snail host, and
• The right fish (cyprinoid fish) as the second intermediate host, and
• A population who eats raw, poorly pickled, smoked, dried or salted freshwater fish

Prevention

• Thoroughly cook all freshwater fish, irradiate or freeze at -10C for at least 5 days
• Educate the public in endemic areas about the dangers of eating raw or improperly cooked fish
• Proper disposal of feces

C. sinensis adult

Photo/Banchob Sripa, Sasithorn Kaewkes, Paiboon Sithithaworn, Eimorn Mairiang, Thewarach Laha, Michael Smout, Chawalit Pairojkul, Vajaraphongsa Bhudhisawasdi, Smarn Tesana, Bandit Thinkamrop, Jeffrey M. Bethony, Alex Loukas & Paul J. Brindley via Wikimedia Commons

Fasciola hepatica

Fasciola hepatica egg  Photo/CDC

General Information

·         Fasciola hepatica is a trematode or fluke also known as the “sheep liver fluke”

·         All trematodes are parasitic

·         All trematodes have a phase of their life cycle in snail or other molluscan host

·         All trematodes are associated with water

·         Facioliasis is a zoonotic disease

Geography

·         Human infection has been reported from over 60 countries, mainly in sheep-raising areas

·         Important public health problem in Latin America (Peru, Bolivia, Cuba), Russia, parts of Europe and Iran

·         Reported sporadically in the US

Morphology (adults)

·         Leaf-shaped with cephalic cone

·         3.0 x 1.3 cm

Morphology (eggs)

·         Large, ovoid, thin-shelled, operculated, yellowish-brown in color

·         130-150 x 90 um in size

Life Cycle

·         Adult fluke in biliary passages

·         Immature eggs are discharged in feces

·         Eggs embryonate in the water

·         Eggs hatch and release miracidia

·         Miracidia invade suitable snail host (intermediate host)

·         Development in snail (sporocyst>rediae>cercariae)

·         Cercariae leaves snail and encyst on aquatic vegetation as metacercariae

·         Metacercariae on uncooked water plant is ingested by human, sheep or cattle (F. gigantica)

·         Metacercariae excyst in the duodenum

·         Migrates through intestinal tract, peritoneal cavity and liver parenchyma into bile ducts

·         Matures into adults

·         Maturation from metacercariae to adult fluke takes up to 4 months

·         In humans, adult flukes can produce eggs for 9 years

Pathology

·         Migrating flukes can cause abdominal pain, liver enlargement and fever

·         Blockage of bile ducts, portal cirrhosis, eosinophilia, jaundice, diarrhea and anemia

·         Halzoun: In humans that eat raw sheep liver. Adult flukes leave liver and attach to throat causing blockage

Diagnosis

·         In endemic areas, symptoms suggest infection

·         History of eating uncooked watercress and water lettuce

·         Finding eggs in feces or biiary drainage. Eggs of F. hepatica and Fasciolopsis buski too similar to differentiate. Check travel history.

·         Antibody detection: enzyme immunoassays (EIA) with excretory-secretory (ES) antigens combined with confirmation of positives by immunoblot

Treatment

·         The drug of choice is triclabendazole with bithionol as an alternative

Epidemiology

·         Sheep-raising countries (and cattle) where there is a suitable snail host (Lymnea sp).

·         Where humans eat uncooked watercress and other aquatic plants in salads or on sandwiches

Prevention and Control

·         Educate public in endemic areas not to eat wild (uncooked) watercress and other water plants

·         Avoid using livestock feces to fertilize water plants

·         Treat animal infections

·         Using molluskicides

Other Information

·         False fascioliasis (pseudofascioliasis): this is the presence of eggs in the stool resulting not from an actual infection but from recent ingestion of infected livers containing eggs. 

·         Have the patient follow a liver-free diet several days and repeat stool examination. 

Adult Fasciola hepatica  Photo/Adam Cuerden via Wikimedia Commons