Sd MEDICAL PARASITOLOGY

CHAPTER 12 | TREMATODES: Flukes | FIRST SEMESTER

3. Schistosoma japonicum (in the
TREMATODES superior mesenteric vein)
● unsegmented helminths, flat, broad
BLOOD FLUKES
and leaf shaped
● have large prominent suckers Schistosoma haematobium
● hermaphrodites except for ● Distribution:
schistosomes - Schistosoma haematobium
● Eggs is endemic in most parts of
- are operculated except for Africa and West Asia
schistosome eggs ● Habitat:
● Snails - The adult worms live in the
- the only intermediate host for vesical and pelvic venous
schistosomes plexuses of humans
- the first intermediate host for
other trematodes Morphology
● Adult male worm
● Metacercaria
- 10–15 mm long by 1 mm
- infective stage for thick
trematodes except for - covered by a finely
schistosomes whereby tuberculated cuticle
cercariae is the infective - has 2 muscular suckers:
stage ● small oral sucker
● large prominent
ventral sucker
- Immediately behind the
ventral sucker and
extending to the caudal
end is the gynecophoric
canal, where the female
worm is found
● Adult female worm
- 20 mm by 0.25 mm
- with the cuticular tubercles
confined to the 2 ends
- gravid female worm
contains 20–30 eggs in its
uterus at one time and may
pass up to 300 eggs a day
● Eggs
- ovoid
- about 150 μm by 50 μm
- non-operculated, with a
terminal spine
- contain ciliated miracidium
- laid in the venules of the
vesical and pelvic plexuses
- from the venules, the eggs
CLASSIFICATION OF TREMATODES OF penetrate the vesical wall
by the action of the spine,
MEDICAL IMPORTANCE BASED ON
assisted by a lytic
HABITAT substance released by the
eggs
- the eggs pass into the
lumen of the urinary
bladder together with some
extravasated blood
- they are excreted in the
urine, more during midday,
particularly towards the
end of micturition
BLOOD FLUKES
- may be found in ectopic
1. Schistosoma haematobium (in the sites such as rectum where
vesical and pelvic venous plexuses) they generally die and
2. Schistosoma mansoni (in the inferior evoke local tissue
mesenteric vein)
 reactions

Pathogenesis and Clinical features

● Cercarial dermatitis presents
with transient itching and petechial
lesions at the site of entry of the
cercariae, more often seen in
visitors to endemic areas than
among locals who may be immune
due to repeated exposure
● Acute systemic schistosomiasis
may cause Katayama fever which
presents with leucocytosis,
eosinophilia and
hepatosplenomegaly
● Clinical features during oviposition
include painless terminal
hematuria.
● Hematuria is initially microscopic,
but become gross in heavy
infection.
● Patients develop frequency of
micturition with burning sensation.
● Cystoscopy shows hyperplasia
Life cycle and inflammation of bladder
1. The eggs are passed in urine (S. mucosa.
haematobium) and in feces (S. ● In the chronic stage, there is
mansoni and S. japonicum) from generalized hyperplasia and
infected humans. fibrosis of the bladder mucosa with
2. Eggs hatch in water releasing a granular appearance (sandy
miracidia. patch).
3. Miracidia penetrate tissue of ● At the sites of deposition of the
freshwater snail (intermediate eggs, there is dense infiltration
host). with lymphocytes, plasma cells
4. Sporocysts develop in snail. and eosinophils.
5. Free swimming cercariae are ● Initially, the trigone (smooth
released by snail into water. triangular region of the internal
6. Cercariae penetrate skin of urinary bladder formed by the two
human. ureteric orifices and the internal
7. Cercariae lose their tails during urethral meatus) is involved, but
penetration and become as it progresses, the entire
schistosomulae. mucosa becomes inflamed,
8-9. The schistosomulae are carried in thickened and ulcerated.
blood circulation and migrate to ● Calculi form in the bladder around
portal blood in liver and mature the eggs and blood clots.
into adults. ● There may be obstructive
10. Paired adult worms migrate to hyperplasia of the ureters and
venous plexus of bladder (S. urethra.
haematobium) or mesenteric ● Chronic urinary
venules (S. mansoni and S. schistosomiasis has been
japonicum) where the female lay associated with squamous cell
their eggs. carcinoma of the bladder

Diagnosis
1. Microscopic examination
● Detection of eggs with
 characteristic terminal Pathogenesis and Clinical features
spines in centrifuged urine ● Cercarial dermatitis may develop
sample. after skin penetration by the
● Eggs which are deposited cercariae.
in rectum may be ● It is self limiting.
occasionally found in ● Katayama fever may develop in
feces. acute infection.
2. Biopsy ● Symptoms of schistosomiasis
● Bladder mucosa or rectal mansoni are mainly intestinal.
biopsies to demonstrate ● Patients develop colicky
eggs. abdominal pain and dysentery,
3. Serodiagnosis which may persist intermittently for
4. Molecular diagnosis many years.
● PCR on clinical samples ● The eggs deposited in the
intestinal wall of colon and rectum,
Treatment cause inflammatory reactions
● Praziquantel (40 mg/kg/day orally causing granulomas, hyperplasia
in 2 divided doses for 1 day) is the and followed by fibrosis.
drug of choice. ● Eggs that are carried through
● Metrifonate is the alternative portal circulation to the liver may
drug. cause hepatosplenomegaly,
periportal fibrosis and portal
Prevention and Control hypertension.
1. Proper disposal of urine and feces
2. Treatment of infected persons Diagnosis
3. Avoid swimming, bathing and 1. Microscopic examination
washing in snail-infested water ● Detection of eggs with
4. Control of snails lateral spines in stool
sample.
● Stool concentration
BLOOD FLUKES methods may be used in
light infection.
Schistosoma mansoni 2. Biopsy
● Distribution: ● Biopsy of rectal mucosa to
- It is widely distributed in demonstrate eggs.
Africa, South America and 3. Serodiagnosis
the Caribbean islands. 4. Molecular diagnosis
● Habitat: ● PCR on stool sample.
- Adult worm lives in the
inferior mesenteric vein. Treatment
● Praziquantel (40 mg/kg/day orally
Morphology in 2 divided doses for 1 day) is the
● Schistosoma mansoni resembles drug of choice.
S. haematobium in morphology ● Oxamniquine is also effective
and life cycles, except the adult
worms Prevention and Control
- smaller 1. Same as S. haematobium
- integuments are covered
with coarse tubercles
- uterus of the gravid BLOOD FLUKES
female contains very few
eggs (1–3 only). Schistosoma japonicum
- egg has a lateral spine - Common name: Oriental blook
fluke
- Distribution:
● Schistosoma japonicum is
found in the Far East,
Japan, China, Taiwan,
Philippines and Sulawesi
- Habitat: The adult worms are
seen in the venules of the superior
mesenteric vein

Morphology
● similar to S. haematobium and S.
mansoni except the adult male is
comparatively slender with smooth
 cuticle. kg/day orally in 2 divided
● uterus of gravid female contains doses for 1 day) is the drug
as many as 100 eggs at one time of choice
and may pass out 3500 eggs daily.
● egg has a small lateral knob
BLOOD FLUKES

Schistosoma mekongi
● First recognized in 1978 and is
found in Thailand, Laos and
Cambodia.
● Morphology:
Life cycle - closely related to S.
1. Similar to S. haematobium japonicum but S. mekongi
eggs are smaller and have
Pathogenesis and Clinical features a small lateral spine.
● pathogenesis is similar to that of - The adult worms are found
S. mansoni, but because of its in the mesenteric venules.
higher egg output, the clinical ● Life cycle:
manifestations are more severe. - Human and dog are the
● During the acute phase, definitive hosts.
Katayama fever is similar to that - Human acquires infection
seen in S. mansoni. through penetration of
● Intestinal manifestations are skin by cercariae.
colicky abdominal pain and ● Pathogenesis:
dysentery. - It produces a mild disease
● Patient may also develop anemia. in humans.
● There is hepatomegaly with ● Treatment:
periportal fibrosis and portal - Praziquantel (60
hypertension mg/kg/day orally in 3
divided doses for 1 day) is
Diagnosis the drug of choice.
● similar to S. mansoni

Treatment Liver flukes

● Praziquantel (60 mg/kg/day orally 1. Clonorchis sinensis
in 3 divided doses for 1 day) is the 2. Opisthorchis viverrini
drug of choice. 3. Fasciola hepatica
Prevention and Control
1. similar to S. haematobium LIVER FLUKES

Clonorchis sinensis
BLOOD FLUKES ● Common name: Chinese liver
fluke, oriental liver fluke
Schistosoma intercalatum
● Distribution: Human
● First recognized in 1934 is found
in West and Central Africa.
clonorchiasis occurs in Japan,
● Morphology: Korea, Taiwan, China and
- Fully embryonated eggs Vietnam
with terminal spines are ● Habitat: Adult worm lives in the
passed in stool. biliary tract.
● Life cycle:
- Human acquires infection Morphology:
through penetration of ● Adult worm has a flat,
skin by cercariae. transparent, spatulate body;
● Pathogenesis: pointed anteriorly and rounded
- adults are found in the posteriorly
mesenteric venules of the ● It is 10–25 mm long and 3–5
colon. mm broad.
- The disease produced in
● adult worm can survive many
human is relatively benign.
● Diagnosis: years in the biliary tract.
- detection of eggs in feces ● worm is hermaphrodite and
and rectal biopsy. passes eggs into the bile duct.
● Treatment: ● The testes of the adult worm
- Praziquantel (40 mg/ are branched.
 ● eggs are broadly ovoid, 30 μm obstruction of the common bile
by 15 μm with a yellowish duct causing cholangitis.
brown (bile-stained) shell. ● Acute presentations are fever,
● It is jug shaped and epigastric pain, diarrhea and
operculated with characteristic hepatomegaly.
shoulders ● Chronic infection may result in
● At the terminal end of the egg, calculus formation. Some
a small knob is sometimes patients may progress to biliary
visible. cirrhosis and portal
● The eggs passed in faeces hypertension.
contain ciliated miracidia ● Clonorchiasis has been
associated with
cholangiocarcinoma.

Diagnosis
1. Microscopic examination
● Detection of eggs in
feces or aspirated bile.
● Identification of adult
worm extracted during
surgical treatment.
2. Serodiagnosis
● Not very useful because
of cross reaction against
other trematodes
Life cycle
1. Embryonated eggs are passed Treatment
out in faeces of infected ● Drug of choice is praziquantel
human. (75 mg/kg/day orally, 3 doses
2. The eggs in water are ingested per day for 2 days).
by freshwater snail. ● Surgical intervention in cases
3. Free swimming cercariae of obstructive jaundice
released by the snail encyst in
the skin or flesh of freshwater Prevention and control
fish. 1. Proper cooking of freshwater
4. The metacercariae in flesh or fish
skin of freshwater fish are 2. Proper disposal of feces
ingested by human host. 3. Control of snails
5-6. The metacercariae excyst in the 4. Treatment of cases
duodenum and adults develop
in the biliary duct
LIVER FLUKES

Opisthorchis viverrini
● Its infection is usually
asymptomatic but may
sometimes resemble
clonorchiasis.
● Distribution:
- common in Thailand and
is associated with
cholangiocarcinoma.
● Life cycle and other features of
Pathogenesis and Clinical features
Opisthorchis are similar to
● In endemic areas, most
Clonorchis.
infected persons are
● Adult worm of Opisthorchis
asymptomatic.
has lobe-shaped testes.
● The migration of the larva up
● egg is similar in morphology to
the bile duct induces
that of Clonorchis.
desquamation, followed by
● Praziquantel (75 mg/kg/day
hyperplasia and adenomatous
orally, 3 doses per day for 2
changes.
days) is the drug of choice
● The adult worm may cause
 Life cycle
LIVER FLUKES 1. Unembryonated eggs are
passed in faeces of infected
Fasciola hepatica human, sheep or cattle.
● Common name: Sheep liver 2. The eggs embryonate in water.
fluke 3. Miracidia hatch and penetrate
● Distribution: It is worldwide in freshwater snail.
distribution, being found mainly 4. In the snail, they undergo
in sheep-rearing countries development to the cercarial
● Habitat: The parasite resides in stage.
the liver and biliary passages of 5. The free swimming cercariae
the definitive host encyst on water plants.
6. The metacercariae on water
plants are ingested by human,
sheep or cattle.
7–8. The metacercariae excyst in the
duodenum and develop into
adults in hepatic biliary ducts.

Morphology:
● adult worm is large,
leaf-shaped fleshy fluke,
measuring 30 mm long and 15
mm broad.
- It has a conical
projection anteriorly with
an oral sucker and is
rounded posteriorly. Pathogenesis and Clinical features
- It is a hermaphrodite. ● Fasciola hepatica causes
● eggs mechanical damage due to its
- are large, ovoid, large size.
operculated, measuring ● It causes parenchymal injury
140 μm by 80 μm in size while passing through the liver
- unembryonated when tissues.
passed in feces. ● Humans develop severe
● Eggs of Fasciola hepatica and inflammatory response as they
Fasciolopsis buski (intestinal are not its primary host.
fluke) cannot be differentiated ● During larval migration, patients
may present with fever, right
upper quadrant pain,
eosinophilia and
hepatomegaly.
● The symptoms subside as
parasites reach the liver.
● In chronic infection, patients
may present with biliary
obstruction, cholelithiasis,
obstructive jaundice, biliary
cirrhosis and anemia.
● Its larvae may undergo ectopic
migration and penetrate
through the diaphragm to reach
the lung.
● Other ectopic sites include
subcutaneous tissue,
genitourinary tract and brain.
Diagnosis a small oral sucker and a large
3. Microscopic examination acetabulum.
● Demonstration of eggs in ● adult worm has a lifespan of
feces or aspirated bile. about 6 months.
4. Serodiagnosis ● Operculated eggs are similar
5. Imaging to those of Fasciola hepatica.
● Ultrasound and CT ● Eggs are laid in the lumen of
abdomen the intestine

Treatment Life cycle

● Triclabendazole (single oral 1. Unembryonated eggs are
dose of 10 mg/kg) is the passed in feces of humans or
treatment of choice. pigs.
● Bithionol is an alternative drug 2. The eggs embryonate in water.
3. Miracidia hatch and penetrate
Prevention and control freshwater snail.
1. Prevent pollution of water 4. In the snail, the miracidia
courses with sheep and cattle develop to the cercarial stage.
feces 5-6. The snail releases free
2. Proper sanitation swimming cercariae. The
3. Wash water cresses and other cercariae develop into
water vegetations, preferably in metacercariae on water plants
hot water or cook well before and are ingested by humans or
consumption pigs causing infection.
7-8. The metacercariae excyst in the
Intestinal flukes duodenum and develop into
1. Fasciolopsis buski adults in the small intestine.
2. Heterophyes heterophyes
3. Metagonimus yokogawai

INTESTINAL FLUKES

Fasciolopsis buski
● Common name: Giant
intestinal fluke
● Distribution: It is a common
parasite of humans and pigs in
China and in Southeast Asian Pathogenesis and Clinical features
countries. ● Adults that attach to the
● Habitat: The adult worm lives duodenal and jejunal mucosa
in the duodenum or jejunum of cause inflammation and local
pigs and humans ulceration.
● In heavy infections, the adult
worms may cause partial
obstruction of the bowel,
malabsorption and
protein-losing enteropathy.
● Clinical manifestations of
fasciolopsiasis are diarrhea
and abdominal pain.

Diagnosis
1. Microscopic examination
● Detection of eggs in
Morphology feces.
● adult is a large fleshy worm, ● Adult worms are rarely
20–75 mm long, 8–20 mm found in fecal specimen
broad and 0.5–3 mm in
thickness. Treatment
● elongated, ovoid in shape, with ● Drug of choice is praziquantel
(75 mg/kg/day orally in 3
 divided doses for 1 day). through ingestion of infected
● Hexylresorcinol and freshwater fish.
tetrachlorethylene have also ● Praziquantel is the drug of
been found useful choice.

Prevention and Control

1. Treatment of infected cases Lung fluke
2. Wash water vegetations, 1. Paragonimus westermani
preferably in hot water or cook
well before consumption LUNG FLUKES
3. Prevent contamination of ponds
and other water sources with Paragonimus westermani
pig or human excreta ● Common name: Oriental lung
4. Control of snails fluke
● Distribution: The parasite is
endemic in Japan, Korea,
INTESTINAL FLUKES Taiwan, China and Southeast
Asian countries.
Heterophyes heterophyes ● Habitat: Adult worms live in the
● smallest intestinal trematode of lungs, usually in pairs in cystic
human. spaces that communicate with
● The infection is prevalent in the bronchi
Nile delta, Turkey and in the
Far East.
● The adult worm lives in the
small intestine and has a
lifespan of about 2 months.
● definitive hosts:
- humans
- cats
- dogs
- foxes
- other fish eating Morphology
mammals ● Adult worm is coffee bean
● Freshwater snail is its first shaped about 10 mm long, 5
intermediate host mm broad and 4 mm thick.
● freshwater fish is the second - reddish brown in color
intermediate host. - Has an oral sucker and a
● Humans acquire infection ventral sucker.
through ingestion of infected - Lifespan of up to 20
freshwater fish. years in humans.
● Praziquantel is the drug of ● Eggs
choice - operculated, golden
brown in colour
- about 100 μm by 50 μm
INTESTINAL FLUKES in size
- unembryonated when
Metagonimus yokogawai freshly laid.
● It is found in the Far East,
northern Siberia, Balkan states Life cycle
and Spain. 1. Unembryonated eggs are
● definitive hosts are: passed out in sputum of
- humans infected human.
- pigs 2-3. Embryonated eggs hatch in
- dogs water to release miracidia
- cats which penetrate freshwater
- pelicans snail.
● first intermediate host is the 4. In the snail, the miracidia
freshwater snail and second develop to the cercarial stage.
intermediate host is the 5. Cercariae released by the snail
freshwater fish. invade the crustacean and
● Humans acquire infection encyst into metacercariae.
 6. Human ingests inadequately ● Bithinol and niclofolan are
cooked or pickled crustaceans also effective
containing metacercariae.
7-8. The metacercariae excyst in the Prevention and Control
duodenum and the larvae 1. Adequate cooking of crabs and
penetrate the intestinal wall and crayfish
migrate to the abdominal cavity, 2. Treatment of infected cases
diaphragm and pleural cavity to 3. Control of snails
the lungs. The larvae mature in
the lungs to adults. Adults in
cystic cavities in lungs lay eggs

Pathogenesis
● In the lungs, the worms live in
cystic spaces surrounded by
fibrous capsule formed by the
host tissues.
● Inflammatory reaction to the
worms and eggs causes
peribronchial granulomatous
lesions, cystic dilatation of
the bronchi, abscesses and
pneumonitis.
● Patients present with cough,
chest pain, dyspnea and
hemoptysis.
● The rusty sputum contains
golden brown eggs.
● Chronic cases may mimic
symptoms of pulmonary
tuberculosis.
Paragonimiasis may also be
extrapulmonary
● Ectopic sites include abdomen
and CNS.
● In the abdomen, it may cause
abdominal pain and diarrhea.
● In the CNS, it may cause
Jacksonian epilepsy. Some
children may present with
mental retardation.

Diagnosis
1. Microscopic examination
● Detection of the eggs in
sputum or faeces(if the
patient swallows the
eggs).
2. Serodiagnosis
3. Molecular diagnosis
● PCR on clinical
specimens.
4. Biopsy
● Identification of species
is made when adult or
egg is recovered from
the lesion in the lungs

Treatment
● Praziquantel (25 mg/kg orally
3 times per day for 2 days) is
the drug of choice.