Coll.

medicine
Lec.5
Parasitology

Prof. Dr. Amal Kh. Kh.

Helminthology
Class: Trematodes

Fasciola hepatica:

Common Name: liver fluke.

History and Distribution F. hepatica was the first trematode that was discovered more than
600 years ago in 1379 by Jehan de Brie. • It was named by Linnaeus in 1758. • It is the
largest and most common liver fluke found in man, however its primary host is the sheep
and to a less extent, cattle. • It causes the economically important disease, "liver rot'; in
sheep.

Habitat The parasite resides in the liver and biliary passages of the definitive host.

Morphology :

Adult worm: • It is large in size, flat leaf-shaped fluke measuring 30 mm long and 15 mm
broad, gray or brown in color. • lt has a conical projection anteriorly containing an oral
sucker and is rounded posteriorly • The adult worm lives in the biliary tract of the definitive
host for many years-about 5 years in sheep and 10 years in humans. • Like all other
trematodes, it is hermaphrodite.

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Egg:

 The eggs are large, ovoid, operculated, bile-stained and about 140 µm by 80 µmin
size.
 Eggs contain an immature larva, the miracidium.
 Eggs do not float in saturated solution of common salt.
 Eggs of F. hepatica and Fasciolopsis buski cannot be differentiated.
• Eggs are unembryonated when freshly passed

Life cycle:

F. hepatica passes its life cycle in one definitive host and two intermediate hosts.

Definitive host: : Sheep, goat, cattle and man.

Intermediate host: Snails of the genus Lymnaea .. Encystment occurs on aquatic plants.

Mode of infection:

 'the definitive host, sheep and man, get infection by ingestion of metacercariae
encysted on aquatic vegetation.
 Adult worm lives in the biliary passage of sheep or man. Eggs are laid in the biliary
passages and are shed in feces.
 the embryo matures in water in about 10 days and the miracidium escapes. It
penetrates the e tissues of first intermediate host, snails of the genus Lymnaea.
 In snail, the miracidium progresses through the sporocyst and the first and second
generation redia stages to become the cercariae in about 1-2 months.
 • the cercariae escape into the water and encyst on aquatic vegetation or blades of
grass to become metacercariae, which can survive for long periods.
 • Sheep, cattle, or humans eating watercress or other water vegetation containing
the melacercaria become infected. the metacercariae excyst in the duodenum of the
definitive host and pierce the gut wall to enter the peritoneal cavity. They penetrate
the Glisson's capsule, traverse the liver parenchyma, and reach the biliary passages,
where they matureinto the adult worms in about 3-4 months.

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Pathogenicity :

Fascioliasis differs from clonorchiasis in that F. hepatica is larger and so causes more
mechanical damage. In traversing the liver tissue, it causes parenchymal injury. As humans
are not its primary host, it causes more severe inflammatory response.

• In acute phase during the migration of the larva, patients present with fever, right upper
quadrant pain, eosinophilia and tender hepatomegaly.

In chronic phase: patients may develop biliary obstruction, biliary cirrhosis, obstructive
jaundice, cholelithiasis and anemia. No association to hepatic malignancy has been
ascribed to fascioliasis.
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Diagnosis:

Stool microscopy:

Demonstration of eggs in feces or aspirated bile from duodenum is the best method of
diagnosis. Eggs of E hepatica and F. buski are indistinguishable.

Serodiagnosis:

Serological tests such as immunofl uorescence, ELISA, immunoelectrophoresis and

complement fixation are helpful in lightly infected individuals for detection of specific
antibody. ELISA becomes positive within 2 weeks of infection and is negative after
treatment. In chronic fascioliasis, Fasciola coproantigen may be detected in stool

Prophylaxis:

Fascioliasis can be prevented by: Health education. Control of snails. Proper disposal of
human, sheep and cattle feces. Proper disinfection of water cresses and other water
vegetations before consumption.

KEY POINTS OF FASCIOLA HEPATICA:

 Largest and most common liver fluke.

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 Large leaf-shaped with a dorsoventrally flattened body.

 Hermaphroditic parasite.
 Eggs are ovoid, operculated and bile-stained.
 Definitive host Primary definitive host is sheep, but it is also found in biliary tract
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of man.
 first intermediate host Fresh water snails (Lymnaea).
 Second intermediate host Aquatic vegetations.
 • Infective form: Metacercariae encysted on raw aquatic vegetations.
 Clinical features: Acute phase-fever, right upper quadrant pain and hepatomegaly.
Chronic phase-biliary obstruction, obstructive jaundice, cholelithiasis and anemia.
 Diagnosis: Detection of eggs in stool and aspirated bile, USG, ERCP and ELISA.
 Treatment: Oral triclabendazole or bithional.
 Prophylaxis: Preventing pollution of water with feces and proper disinfection.

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Clonorchis Sinensis

Common Name :The Chinese liver fluke and oriental liver fluke.

History and Distribution:

C. sinensis was first described in 1875 by McConnell in the biliary tract of a Chinese
carpenter in Calcutta Medical College Hospital. • Complete life cycle of Clonorchis was
worked out by Faust and Khaw in 1927. • Human clonorchiasis occurs in Japan, Korea,
Taiwan, China and Vietnam, affecting about 10 million persons.

Habitat Adult worm lives in the biliary tract and sometimes in the pancreatic duct.

Morphology:

 Adult worm: It has a flat transparent, spatulate body; pointed anteriorly and rounded
posteriorly .
 It is 10- 25 mm long and 3-5 mm broad.
 The adult worm can survive in the biliary tract for 15 years or more.
 The hermaphroditic worm discharges eggs into the bile duct.
 Eggs: Eggs are flask-shaped, 35 µm by20 µm with a yellowish - brown (bile-stained)
shell.
 It is operculated at one pole and possesses a tiny knob at the other pole and a small
hook-like spine at the other .
 Eggs do not float in saturated solution of common salt.
 The eggs passed in feces contain the ciliated miracidia.

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Life Cycle :

Definitive host: Humans are the principal definitive host, but dogs and other fish -eating
canines act as reservoir hosts. Intermediate hosts: Two intermediate hosts are required to
complete its life cycle, the first being snail and the second being.fish. Infective form:
Metacercaria larva. Mode of infection: Man acquires infection by eating undercooked
freshwater fish carrying metacercariae larvae. Clonorchis eggs although embryonated do
not hatch in water, but only when ingested by suitable species of operculate snails (first
intermediate host), such as Parafossarulus, Bulimus, or Alocinma species. The miracidium
develops through the sporocyst and redia stages to become the lophocercus cercaria with a
large fluted tail in about 3 weeks . The cercariae escape from the snail and swim about in
water, waiting to get attached to the second intermediate host, suitable freshwater fish of
the Carp family. The cercariae shed their tails and encyst under the scales or in the flesh of
the fish to become metacercariae, in about 3 weeks, which are the infective stage for
humans.

Infection occurs when such fish are eaten raw or inadequately processed by h uman or other
defini tive hosts. Frozen, dried, or pickled fish may act as source of infection . Infection
may also occur through fingers or cooking uten sils contaminated with the metacercariae
during preparation of the fish for cooking. • The metacercariae excyst in the duodenum of
the definitive host. • The adolescaria that come out, enter the common bile duct through
the ampulla of Vater a nd proceed to thedistal bile capillaries, where th ey marure in about
a month and assume the adult form . • Adult worms produce an average of 10, 000 eggs
per day, which exit the bile ducts and are excreted in the feces. The cycle is then repeated.

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Pathogenicity:

The migration of the larva up the bile duct induces desquamation, followed by hyperplasia,
and sometimes, adenomatous changes. The smaller bile ducts undergo cystic dilatation.

The adult worms may obstruct and block the common bile duct leading to cholangitis. •
Patients in the early stage have fever, epigastric pain, diarrhea and tender hepatomegaly.
This is followed by biliary colic, jaundice and progressive liver enlargement. Many
infections are asymptomatic. • Chronic infection may result in calculus formation. • A few
cases go on to biliary cirrhosis and portal hypertension. • Some patients with chronic
clonorchiasis tend to become biliary carriers of typhoid bacilli. • Chronic infection has also
been linked with cholangiocarcinoma.

Diagnosis :

1he eggs may be demonstrated in feces (stool microscopy) or aspirated bile. They do not
float in concentrated saline. • Several serological tests have been described including
complement fixation and gel precipitation but extensive cross-reactions limit their utility.
!HA with a saline extract of etherized worms has been reported to be sensitive and specific.
• Intradermal allergic tests have also been described.

Treatment Drug of choice is praziquantel 25 mg/ kg, three doses in l day. Surgical
intervention may become necessary in cases with obstructive jaundice.

Prophylaxis Clonorchiasis can be prevented by: • Proper cooking of fish. • Proper disposal
of feces. • Control of snails.

• INTESTINAL FLUKES

A number of flukes parasitize the human small intestine. These include Fasciolopsis buski,
H. heterophyes, Metagonimus yokogawai, .

Fasciolopsis buski :

Common Name Giant intestinal fluke

History and Distribution:

It was first described by Busk in 1843 in the duodenum of an East Indian sailor, who died
in London. • It is the largest and most common intestinal fluke of man and pigs. • Mainly
found in China and in Southeast Asian countries. • In India it occurs in Assam, Bengal,
Bihar and Odisha. • Prevalence rate is as high as 22.4% in India. • Children are more prone
to infection than adults as they enjoy playing in water.

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Habitat :

The adult worm lives in the duodenum or jejunum of pigs and man.

Morphology

Adult worm: The adult is a large fleshy worm, 20-75 mm long and 8- 20 mm broad and
0.5-3 mm in thickness.

Largest trematode infecting humans: Fasciolopsis buski

• Smallest trematode infecting humans: heterophyes

• It is elongated ovoid in shape, with a small oral sucker and a large acetabulum. lt has no
cephalic cone as in F. hepatica . • The adult worm has a lifespan of about 6 months. • The
two intestinal caeca do not bear any branches .

Eggs: • The operculated eggs are similar 10 those of F. hepatica . • Eggs are laid in the
lumen of the intestine in large numbers, about 25,000 per day.

Life Cycle:

F. buski passes its life cycle in one definitive host and two intermediate host. Definitive
host: Man and pigs. Pigs serve as a reservoir of infection for man. First intermediate host:
Snails of the genus Segmentina. Second intermediate host: Encystment occurs on aquatic
plants, roots of the lotus, bulb of the water chestnut which act as second intermediate host.

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Infective form: Encysted metacercariae on aquatic vegetation. • The eggs passed in feces
of definitive host hatch in waler in about 6 weeks, releasing the miracidia which swim
about. • On coming in contact wilh a suitable molluscan intermediate host, snails of the
genus Segmentina, miracidia penetrates its tissues to undergo development in the next few
weeks as sporocyst, first and second generation rediae and cercariae . • The cercariae,
which escape from the snail, encyst on the roots of the lotus, bulb of the water chestnut,
water hyacinth and on other aquatic vegetations. • When they are eaten by man, the
metacercariae excysts in the duodenum, become allached to the mucosa and develop into
adults in about 3 months .

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Pathogenesis:

The pathogenesis of fasciolopsiasis is due to traumatic, mechanical and toxic effects. •

Larvae that attach to the duodenal and jejuna! mucosa cause inflammation and local
ulceration. Intoxication and sensitization also account for clinical illness.

In heavy infections, the adult worms cause partial obstruction of the bowel, malabsorption,
protein-losing enteropathy and impaired vitamin B12 absorption. • ·the initial symptoms
are diarrhea and abdominal pain. • Toxic and allergic symptoms appear usually as edema,
ascites, anemia, prostration and persistent diarrhea. • Paralytic ileus is a rare complication.
Laboratory Diagnosis History of residence in endemic areas suggests the diagnosis, which
is confirmed by demonstration of the egg in feces or of the worms after administration of
a purgative or anthelmintic drug.

Treatment

Drug of choice is praziquantel.

Prophylaxis :

• Treatment of infected persons. • Proper disinfection of water vegetables, by hot water. •

Prevention of polution of water resources from human and pig feces.

Community-based praziquantel treatment can be used to control infection. • Control of

snails.

Heterophyes heterophyes:

This is the smallest trematode parasite of man. • the infection is prevalent in the Nile delta,
Turkey and in the Far East. • The worm has been reported in a dog in India. • The adult
worm lives in the small intestine and has a lifespan of about 2 months.

Definitive Hosts Humans, cats, dogs, foxes and other fish-eating mammals. First
Intermediate Host Snails of the genera Pironella Second Intermediate Host Fishes, such as
the mullet and tilapia; encystment occurs in fishes. • Man acquires infection by eating raw
or undercooked fishes containing metacercaria. • In the small intestine, it can induce
mucous diarrhea and colicky pains. • Ectopic lesions may occur as granulomas in
myocardium, brain and spinal cord. • Diagnosis is based on the finding of a minute
operculated egg in the stool.

Drug of Choice Praziquantel.

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Morphology and life cycle:

The mature Heterophyes heterophyes is a minute pyriform worm, broadly rounded

posteriorly and somewhat narrower anteriorly. It measures 1 to 1.7 mm. in length by 0.3 to
0.4 mm. in breadth. It is covered with minute spines set close together. The eggs are small
(28 to 30 micron by 15 to 17 microns), have a conspicuous conical operculum, and each
contains a mature miracidium.

When these egg are ingested by Pirenella conica (Egypt) or Cerithedia cingulata (Japan),
they hatch and proceed with their intra-molluskan stages of development. The cercariae
which escape from the mollusk encyst superficially in fresh or brackish-water fishes, which
constitute the source of infection for man.

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Metagonimus Yokogawai:

It is found in the Far East, Northern Siberia, Balkan states and Spain. Definitive Hosts
Humans, pigs, dogs, cats and pelicans. First Intermediate Host Freshwater snail Cerithidea..
Second Intermediate Host Fish. • Definitive hosts are infected by eating raw fish containing
the metacercariae. • Pathogenic effects consist of mucous diarrhea and ectopic lesions in
myocardium and central nervous system as in heterophyasis. Drug of Choice Praziquantel.

Morphology and life cycle of Metagonimus yokogawai :

Metagonimus yokogawai resembles H. heterophyes in its habitat in the definitive host, its
shape, size (1 to 2.5 mm. by 0.4 to 0.75 mm.) and its life cycle. The snail hosts are species
Thiara,, which ingest the eggs and in which the miracidia transform into sporocysts, with
two successive generations of rediae and finally the development of cercariae having a pair
of pigmented “eye-spots” and a dorsal and a ventral fluted tail fin. The cercariae which
escape from the snail host become attached to fresh-water fishes and encyst under the skin.
Consumption of uncooked infected fish provides opportunity for infection of the definitive
host.

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Symptoms and pathogenesis :

Attached to intestinal wall , the adult worm produce no symptoms unless present in large
numbers . Chronic intermittent diarrhea , nausea, and vague abdominal complaints have
been reported . occasionally the worm invade the mucosa , and their eggs deposited in the
tissues may gain access to the circulation to embolize to the brain , spinal cord or heart .
neurologic deficits , and cardiac insufficiency have been ascribed to granulomas that form
around these eggs.

Diagnosis , treatment and prevention :

This is based on recovery of the eggs in the stool . praziquantel is the of choice (25mg\kg
tid for 1 day) . prevention can be effected by the through cooking of all fish intended for
human consumption.

• LUNG FLUKES :

Paragonimus Westermani :

Common Name Oriental lung fluke. History and Distribution P. westermani was
discovered in 1878 by Kerbert in the I ungs of a Bengal tiger captured in India that died in
the zoological gardens at Amsterdam. • The parasite is endemic in the Far East-Japan,
Korea, Taiwan, China and South East Asia- Sri Lanka and India. • Th ere are about 40
species of Paragonimus that infect mammals. • ln India, cases have been reported from
Assam, Bengal, TamiI Nadu, Kerala, Manipur, Sikkim, Arunachal Pradesh and Nagaland.
• P. westermani is the most common species infecting human. • Endemic foci of P.
westermani and P heterotremus are present in Manipur. • lt is an important human pathogen
in Central and South America.

Morphology:

Adult worm:

 The adult worm is egg-shaped about 10 mm long, 5 mm broad and 4 mm thick and
reddish-brown in color
 The integument is covered with scale-like spines.
 It has an oral sucker placed anteriorly and a ventral sucker located towards the middle
of the body .
 It has two un branched intestinal caeca which end blindly in the caudal area.
 They have a lifespan of up to 20 years in humans.
 Egg:The eggs are operculated,golden-brown in color and about 100 µm by 50 µmin
size .

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  They are unemb1yonated when freshly laid.

Habitat:

Adults worms live in the lungs, usually in pairs in cystic spaces that communicate with
bronchi .

Life Cycle:

Definitive host: Man. Besides humans, other definitive hosts include cats, tigers, leopards,
foxes, dogs, pigs, beavers, mongoose, and many other crab-eating mammals and domestic
animals.

First intermediate host: Freshwater snail, belonging lo the genera Semisulcospira and
Brotia. Second intermediate host: Freshwater crab or crayfish. Infective form:
Metacercariae encysted in crab or crayfish.

Mode of infection: Man acquires infection by eating undercooked crab or crayfish

containing metacercariae. • The adull worms live in the respiratory tract of the definitive
host. • Unembryonated eggs escape into the bronchi and are coughed up and voided in
sputum or swallowed a nd passed in feces . • The eggs mature in about 2 weeks and hatch
to release free-swimming miracidia. • These infect the.first intermediate molluscan host,
snails belonging to the genera Semisulcospira and Brotia. • Cercariae that are released from
the snails after several weeks are microcercus, having a short stumpy tail. • The cercariae
that swim about in streams are drawn into the gill chambers of the second intermediate
crustacean host, crabs or crayfish . • they encyst in the gills or muscles as metacercariae. •

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Definitive hosts are infected when they eat such crabs or crayfish raw or inadequately
cooked. • The metacercariae excyst in the duodenum and the adolescariae penetrate the gut
wall, reaching the abdominal cavity in a few hours. They then migrate up through the
diaphragm into the pleural cavity and lungs finally reaching in the vicinity of the bronchi,
where they develop into adult worms in 2-3 months . The worm is hermaphroditic but
usually it takes 2 for fertilization.

Pathogenicity and Clinical Features

Pulmonary features: In the lungs, the worms lie in cystic spaces surrounded by a fibrous
capsule formed by the host tissues. The cysts, about a centimeter in diameter are usually in
communication with a bronchus. Inflammatory reaction to the worms and their eggs lead
to peribronchial granulomatous lesions, cystic dilatation of the bronchi, abscesses,
pneumonitis and eosinophilia. • Patients present with cough, chest pain and hemoptysis.
The viscous sputum is speckled with the golden-brown eggs. Occasionally, the hemoptysis
may be profuse. • Chronic cases may resemble pulmonary tuberculosis.

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Diagnosis :

Microscopy: Demonstration of the eggs in sputum provides definitive evidence. Sputum

examination should be repeated for 7 consecutive days.

Serology: Complement fixation test is positive only during and shortly after active
infection, while the intradermal test remains positive for much longer periods. Parasite-
specific immunoglobulin E (lgE) and antiparagonimus antibodies can be detected in serum.
• Indirect hemagglutination and ELISA tests are highly sensitive. they become negative
within 3-4 months after successful treatment.

Computed tomography scan of chest also helps in diagnosis of pulmonary lesions "Soap-
bubble'' like appearance .

Treatment • Praziquantel (25 mg/ kg TDS for 1-2 days) is the drug of choice. • Bithionol
and niclofolan are also effective in treatment.

Prophylaxis:

Adequate cooking of crabs and crayfish and washing lhe hands after preparing them for
food.

Treatment of infected persons. • Disinfection of sputum and feces. • Eradication of

molluscan hosts.

GOOD LUCK …….Prof. Amal KH. KHalaf

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