Taenia saginata

T. saginata adult/CDC

General Information

• Beef tapeworm
• Definitive host is humans, herbivores are intermediate hosts

Geography

• Worldwide, particularly where beef is eaten raw or undercooked

Morphology (adults)

• Strobila is 15-20 ft
• 1000-3000 proglottids
• Gravid proglottids are longer than wide
• Mature proglottid has 12-30 lateral uterine branches, can be differentiated from Taenia solium (7-13)
• Quadrate (four suckers), unarmed scolex

Morphology (eggs)

• 30-35 um in diameter, radial striated
• Internal oncosphere contains three pairs of hooklets
• Indistinguishable from Taenia solium eggs

Life Cycle

• Adult in small intestine
• Gravid proglottids with infective eggs passed in feces
• Eggs can survive for months in the environment
• Eggs ingested by cattle
• Eggs hatch> onchospheres released> invade intestinal wall> becomes lodged in striated muscle
• Develop into cysticerci (survive for years)
• Humans are infected by eating raw or undercooked beef
• Cysticerci attach to small intestine and mature to adults

Pathology

• Most patients asymptomatic
• Mild abdominal symptoms
• Migrating proglottids- appendicitis or cholangitis possible

Diagnosis

• Identification to the species level not possible based solely on microscopic exam of eggs
• Egg stage a potential health hazard (T. solium)
• Identification of proglottids and/or scolex

Treatment

• Praziquantel or niclosamide

Epidemiology

• Cattle infected while grazing on contaminated vegetation

Prevention

• Cook beef thoroughly

T. saginata proglottid

T. saginata scolex

Taenia spp. egg

Diphyllobothrium latum

D. latum egg/CDC

General Information

• Also known as "Fish Tapeworm" and "Broad Tapeworm"
• Largest human tapeworm, strobila can reach 30-45 ft in length

Geography

• Worldwide, particularly in cool lake regions of the Northern hemisphere (North America, Europe and Asia) and South America

Morphology (adults)

• 30-45 ft in length, 1 cm in width
• Scolex (head) spatulate with two slit-like grooves (bothria)
• 3000 proglottids, each with "rosette-shaped" uterus. 
• Proglottids wider than long

Morphology (eggs)

• Oval or ellipsoidal, 75 um x 45 um
• Operculated
• Undeveloped embryo (coracidium)
• Small, terminal abopercular knob

Life Cycle

• Adult in small intestine
• Immature eggs shed from gravid proglottids, passed in feces
• Eggs develop in fresh water> develop into coracidium
• Coracidium emerge from egg, ingested by freshwater crustacean (copepod, Cyclops sp.) First intermediate host
• Develops into procercoid larva
• Infected crustacean ingested by small freshwater fish (minnows for example) (second intermediate host)> develops into plerocercoid larva (sparganum)
• Infected small fish ingested by larger "predatory fish" (perch, trout, etc)> plerocercoid larva released and penetrates muscles of predator fish
• Humans infected when consuming raw or undercooked infected fish
• Plerocercoid larva develops to adult in small intestine
• From beginning of infection> approximately 6 weeks until eggs passed in feces
• Adult can live for up to 20 years, each adult can shed 1 million eggs/day

Pathology

• Usually asymptomatic, patient becomes aware when worm segments passed in stool
• Clinical manifestations may include pernicious anemia due to vitamin B12 deficiency
• Abdominal discomfort, diarrhea, vomited, weight loss
• Heavy infections can result in intestinal obstruction

Diagnosis

• Microscopic identification of eggs in stool sample. Examination of characteristic proglottids also useful.

Treatment

• Praziquantel or nicolsamide

Epidemiology

• Freshwater transmission dependent on available human/mammal definitive host, suitable intermediate hosts, consumption of raw or undercooked freshwater fish
• Pollution of freshwater with infected human feces

Prevention

• Thorough cooking of freshwater fish, or
• Freezing fish for 24 hours at -18C (0F), or
• Irradiation

D. latum gravid proglottids/CDC

The Schistosomes

S. mansoni adults/CDC

General Information

• Trematodes from the genus Schistosoma that live in the blood vessels of humans and other mammals
• Adults have separate sexes (different from other trematodes)
• Disease called schistosomiasis or Bilharziasis, named after Theodore Bilharz
• Can cause acute and chronic disease, a disease-complex
• Most important helminth infection in terms of worldwide distribution, prevalence and morbidity
• Sometimes considered a "man-made" disease with the construction of hydroelectric dams and irrigation systems in developing nations
• The three most important human species are Schistosoma mansoni, S. haemotobium and S. japonicum

Geography

• S. mansoni is found in Africa (including Madagascar), the Arabian Peninsula, Brazil, Suriname, Venezuela and some Caribbean islands
• S. haemotobium is found in Africa and the Middle East
• S. japonicum is found in China, the Philippines and parts of Indonesia

Morphology (adults)

• Separate sexes
• Cylindrical in shape
• Male: short (10-20 mm in length) with copulatory groove
• Female: Long and slender (20-26 mm in length)

Morphology (eggs)

• S. mansoni: 180 um x 80 um, developed miracidium and a large lateral spine
• S. haemotobium: 160 um x 80 um, developed miricidium and a large terminal spine
• S. japonicum: 80 um x 60 um, developed miricidium and a small lateral knob (spine)

Life Cycle

• Eggs laid in blood vessels, pass from vessels into tissue, some reach the intestine  or bladder, excreted in the feces or urine
• Eggs that reach freshwater, miricidia hatches, swims to find appropriate snail host (intermediate) and penetrate
• In the snail- two generations of sporocysts> produce cercariae> cercariae migrate out of snail into water (Snail cycle requires 3-5 weeks)
• Cercariae: 0.1-0.2 mm in length, fork-tailed (infective stage) swims to find human host
• Penetrates through skin or mucous membranes
• Loses tail upon penetration> schistosomula
• Schistosomula enter peripheral veins> pass through heart, lungs to portal veins> to intestinal or bladder veins depending on species
• Adults have long life span 5-7 years and up to 30 years
• Eggs appear in feces or urine 1-3 months after cercarial penetration

Pathology

• Itchy papular eruption during cercarial penetration
• Response to antigenic and toxic secretions of larval and adult worms and eggs
• Acute stage- Katayama syndrome: fever, chills , nausea, abdominal pain, marked eosinophilia, enlarged and tender liver
• Daily egg outputs: S. haemotoboium 100, S. mansoni 300 and S. japonicum 1000-3500
• Late complications from chronic infections include liver fibrosis, portal hypertension and its sequelae
• Bowel obstruction, uropathy, superimposed bacterial infection (Salmonella) and bladder cancer
• Eggs depositied in ectopic sites like brain, spinal cord

Diagnosis

• Microscopic identification of eggs in stool or urine is the most practical method for diagnosis. Stool examination should be performed when infection with S. mansoni or S. japonicum is suspected, and urine examination should be performed if S. haematobium is suspected. 
• Kato-Katz, Ritchie technique
• Antibody detection

Treatment

• Infections with all major Schistosoma species can be treated with praziquantel

Epidemiology

• Exposure to contaminated freshwater that is used for agricultural, household, industrial or recreational purposes

Prevention

• Prevent exposure to contaminated freshwater
• Proper disposition of feces and urine 
• Educating the public, treatment
• Molluskicides for treating snail-breeding sites

S. haemotobium egg/CDC

S. mansoni egg/CDC

S. japonicum egg/CDC

Fasciolopsis buski

Fasciolopsis buski egg/CDC

General Information

• Human intestinal trematodiases are associated with eating habits
• They are localized to areas where there is water, snail vectors and reservoir hosts

Geography

• Widely found in rural southeast Asia, in particular central and south China, parts of India and Thailand

Morphology (adults)

• Fasciolopsis buski is the largest fluke to infect humans, aka Giant Intestinal Fluke
• 7.0 x 1.5 cm
• Large, leaf-shaped, lacks a cephalic cone

Morphology (eggs)

• Large, thin-shelled, unembryonated, operculated
• 130-150 x 78-98 um
• Found in large numbers in feces, too similar to F. hepatica to differentiate

Life Cycle

• Adults in the small intestine
• Eggs pass in feces to water where they embryonic
• After few weeks, miracidium emerges
• Miracidium swims to find suitable snail (Segmentina sp.) as first intermediate host
• In the snail-sporocysts>rediae>cercariae
• Cercariae released from snail to water
• Encyst on aquatic plant as metacercariae
• Plant eaten raw by mammalian host (humans and pigs)
• Metacercariae excysts and attach to the gut mucosa
• Develop into adults in about 3 months
• Lives for one year

Pathology

• More worms, more disease- usually asymptomatic
• Large number of worms attaching to mucosa - bleeding, inflammation and ulceration
• Diarrhea (foul smelling greenish-yellow stools), abdominal pain, intestinal obstruction, edema
• Toxic products from worms may be absorbed and cause toxemia
• Death is rare

Diagnosis

• Travel history
• Demonstration of eggs in feces or vomit (eggs indistinguishable from F. hepatica)
• Rarely by identifying adult fluke

Treatment

• Praziquantel is the drug of choice

Epidemiology

• Pigs are reservoir hosts
• Metacercariae encysts on hard surface, particularly water plants like water caltrop and water chestnuts
• The outer cover of plant is peeled off with teeth and metacercariae are released into the mouth
• Children more frequently infected--eat water plants going to and from school

Prevention

• Treatment
• Education
• Changing eating habits- do not eat without boiling first
• Keep pigs from contaminating areas where water plants grow
• Do not feed water plants to pigs

F. buski Life Cycle

 

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