2. A Parasite is an organism that spends
a significant portion of its life in or on the
living tissue of a host organism & which
causes harm to the host without
immediately killing it.
Every free-living species has its own
unique species of parasite, so the number
of parasitic species greatly exceeds the
number of free living species.
3. PARASITOLOGY & MEDICAL PARASITOLOGY:
• It is the study of parasites, their hosts & the relationship
between them.
• One of the largest fields in parasitolgy, medical
parasitology is the subhect which deals with the
parasites that infect humans, the diseases caused by
them, clinical picture and the response generated by
humans against them. It is also concerned with the
various methods of their diagnosis, treatment & finally
their prevention & control.
5. TREMATODES-FLAT WORMS(FLUKES)
• Opisthorchis
• O. sinensis
• O. felineus
• O. viverini
• Paragonimus
• P. westermani
• P. kellicotti
• Echinostoma
• Schistosoma
• S. mansoni
• S. hematobium
• S. japonicum
• Fasciolopsis
• Fasciolopsis buski
• Fasiola
• Fasiola hepatica
• Fasiola gigantica
6. Trematodes: Morphological Features
• Mouth connects to pharynx,
leads to esophagus, bifurcates
into 2 ceca
• No anus: releases cecal contents
back through mouth into tissue
it infects
• Cecal contents can be seen in
histopathologic section and are
colloquially referred to as “fluke
puke”
• Also possess and acetabulum, or
ventral sucker – holdfast organ
not associated with feeding
• Near anterior end, mouth
is surrounded by muscular
oral sucker
7. Trematodes: Reproduction
• With exception of
schistosomes (blood flukes) all
flukes are hermaphroditic
• Each fluke possesses both sex
organs
• Self-fertilization usually takes
place, but cross-fertalization
can also occur
8. Fasciola hepatica
• Fasciola hepatica, also known as the common liver
fluke or sheep liver fluke.
• Is a parasitic flatworm of the class Trematoda,
phylum Platyhelminthes that infects liver of various
mammals, including humans.
• The disease caused by the fluke is called fascioliasis
(also known as fasciolosis).
• F. hepatica is world-wide distributed and causes
great economic losses in sheep and cattle.
9. • Definitive host:
• Sheep
• Cattle
• Humans (Accidental)
• Other Mammals
• Intermediate host:
• Fresh Water Snail
• Geographic Range:
• Cosmopolitan; anywhere sheep and cattle are
raised
14. Life cycle outside the animal
• Eggs hatch in spring (>10 °C) to release miracidia
which must penetrate a mud snail (Lymnaea [syn.
Galba] truncatula) within 3 hours
• Develop inside snail
• Cercariae emerge from snail
• Encyst on grass (metacercariae)
• Infection of a snail with one miracidium can produce
over 600 metacercariae
15. Life cycle inside the animal
• Once ingested metacercariae excyst in SI and
immature fluke migrate through the gut wall to
penetrate the liver
• Tunnel through liver for 6-8 weeks before entering
bile ducts where they reach maturity
• Time from infection of cattle/sheep to adult egg-
laying fluke is 10-12 weeks
• Little or no development of immunity
16. Cycle of Events in Fasciola hepatica
• The life cycle of Fasciola hepatica starts
when a female lays eggs in the liver of an
infected human. Immature eggs are
discharged in the biliary ducts and taken out
in the feces. If landed in water, the eggs
become embryonated and develop larvae
called miracidia. A miracidium invades an
aquatic snail and develops into cercaria, a
larva that is capable of swimming with its
large tail.
DR.T.V.RAO MD 16
17. • The cercaria exits and
finds aquatic vegetation
where it forms a cyst
called Metacercariae. A
human eats the raw
freshwater plant
containing the cyst.The
Metacercariae excysts in
the first part of the small
intestine, duodenum. It
then penetrates the
intestinal wall and gets
into the peritoneal cavity.
Cycle of events in infection
DR.T.V.RAO MD 17
18. Cycle of events in infection
• It finds the liver and starts eating liver cells.
This happens only a few days after the initial
contact with the parasite. Usually the larva
spends a few weeks just browsing and
eating the liver.Then it relocates to the bile
duct where it begins its final stage and
becomes an adult. It takes about three
months for the Metacercariae to develop
into an adult.Adults are about 3 cm long and
1 cm wide.Adult females can produce up to
25000 eggs per day.
DR.T.V.RAO MD 18
19. • Ingestion
Metacercariae
• Ex-cyst in
Duodenum
• Burrows through
Intestinal Wall
• Enters Peritoneal
Cavity
• Migrates to Liver
Progress of Infection
DR.T.V.RAO MD 19
23. egg capsule with emerging
miracidium of Fasciola
hepatica. 400x
unembryonated egg
capsule of F. hepatica.
earlier stage of
development. 400x
embryonated egg
capsule of Fasciola
hepatica. So-named
because the
miracidium is fully
formed and ready to
emerge. The
operculum can be seen
to the left. 400x
24. Redia and cercaria of Fasciola
hepatica
Miracidium of Fasciola hepatica.
This ciliated, non-feeding larval
stage, has about 24 hours to find
its specific snail host, such as
Fossaria modicella or Stagnicola
bulimoides. 400x
25. The ova
Length 130-145 µm
Width 70-90 µm
Regular ellipse
Thin shell
Operculum at one pole
Granular yellowish-brown contents filling whole egg
26. The Adult
• one of the largest flukes in the world.
• 20 -30mm in length and 13 mm in width
• Leaf shape characteristic with the
anterior end broader than the posterior
end and an anterior cone-shaped
projection.
• Possesses a powerful oral sucker at the
anterior cone and a ventral sucker at
the base of the cone attach to the
lining of the biliary ducts.
• monoecious - possesses ovaries and
testes which are highly branched and
allow for individual flukes to produce
eggs independently.
27. A stained adult Fasciola
hepatica; approximate length =
20 mm.
The internal organs are highly
branched, thus making it very
difficult to differentiate the
various internal organs
All of their major systems
are branched, including
the intestine, testes, and
ovary.
28.
29. F.hepatica, adult worm, macroscopic
examination:
adults measure 2-5 cm by 8-13 mm, are
flat, oval in shape with a cephalic cone
containing the oral sucker.The adults
live in biliary ducts for up to 10 years.
Fasciola hepatica, living adult in bile duct of sheep.
30. F.hepatica, adult
worm, liver biopsy:
after excistation in
the small intestine,
metacercariae
penetrate the
intestinal wall and
the Glisson capsule,
cross the liver
parenchima to the
bile ducts.Eggs can
be found in faeces 3-
4 months after
penetration.
33. • The first stage: prepatent or larval period:
• Abdominal Pain
• Fever
• Backache, headache
• Chills
• Weight loss
• Urticaria
• Eosinophilia, elevation of AST, ALT
• Cough and chest discomfort
• The second stage: patent or biliary period:
• Intermittent right upper quadrant pain
• Enlarged, tender liver
• Diarrhea
• Eosinophilia
• Complications:
• Anemia, cholangitis, biliary obstruction, subcapsular liver
hematomas, hemoperitoneum
Symptoms
34. Condemned Liver
Annual
condemnation
of livers of 3-4%
of cattle at $3-5
each due to
parasites.
•Adult-Biliary hyperplasia,
dilatation, fibrosis,
calcification
•Migration-Diffuse
fibrosis, shrunken ventral
lobe
35. • The course of infection passes through three phases:
• The acute phase
• The chronic phase
• The obstructive phase
• Pathology / clinical manifestations are related to the phase
36. • Acute Phase:
• Rarely seen in humans and occurs only when a large
number of metacercariae are ingested at once.
• Fever, tender hepatomegaly, and abdominal pain are the
most frequent symptoms of this stage of infection
• vomiting, diarrhea, urticaria (hives), anemia, may be
present.
• Caused by the migration of the F. hepatica larvae
throughout the liver parenchyma.
• The larvae penetrate the liver capsule and begin to produce
symptoms 4-7 days after ingestion.
• Migration and acute phase continues for 6-8 weeks until
the larvae mature and settle in the bile ducts.
37. The acute phase:
• Coincides with migration of
the immature flukes
through the peritoneal
cavity, penetrating liver
capsule then through
liver parenchyma till they
reach the bile ducts.
liver
38. Symptoms :
• Acute symptoms
• Asymptomatic (unusual)
• Severe illness
(prostration & jaundice)
(unusual)
• Acute dyspepsia
• Prolonged high fever
• Hepatomegaly/
abdominal pain in the
right hypochondrium
•Urticaria
•Peripheral
eosinophilia, up to
80%.
•Anaemia
39. Cont..
• Chronic Phase:
• more common in human
• include biliary cholic, abdominal pain, tender hepatomegaly,
and jaundice.
• In children, severe anemia - common result of infection
• biliary obstruction and inflammation caused by the
presence of the large adult worms and their metabolic waste in
the bile ducts.
• Inflammation of the bile ducts leads to fibrosis and a
condition called "pipestem liver", (white appearance of the
biliary ducts after fibrosis).
• The final outcome portal cirrhosis and even death.
40. • The chronic phase,
coincides with the
presence of the flukes
in the bile ducts
• The life span of the
parasite is 10-13 years
• Pathology tends to be
mild
41. Symptoms :
• Asymptomatic
Few gastrointestinal symptoms
• Intermittent fever with persistent prominent
eosinophilia
Recurrences of the acute signs & symptoms
Recurrent cholangitis
42. Obstructive phase
(heavy / prolonged
infection)
Coincides with epithelial
changes in the bile ducts
due to irritation of the
epithelium
by the spines
& the activity of proline
45. Laboratory diagnosis
• The definitive and most widely used form of diagnosis is the directly
observed presence of Fasciola hepatica eggs either in a stool sample,
duodenal aspirate or biliary aspirate.
• However, the flukes do not begin to produce eggs until roughly 4 months
after infection.
• Until this time and in the case of ectopic infections where eggs are not
present in the stool, serological tests can be used, the FAST-ELISA being
the most popular.
• It has a sensitivity of 95% and can detect specific F. hepatic antibodies as
early as 2 weeks after infection .
• Ultrasound can be used to visualize the adult flukes in the bile ducts
• CT scan may reveal the burrow tracts made by the worms and dilation of
the bile ducts.
46. Computed tomography (CT) and magnetic-resonance-imaging (MRI)are used for
further characterization of the lesion.They are indispensable for the evaluation of
extrahepatic affection in AE and they are used for a preoperative evaluation.CT best
depicts the typical calcifications and it is used for follow-up examinations at longer
intervalls. For serology an ELISA was established based on the purified
E.multilocularis
carbohydrate antigen Em2 (derived from the laminated layer).
It is the reference test for diagnosis and it may allow discrimination of AE from
E.granulosus infection.However, in a significant percentage of cases the two species
can not be differentiated simply by serological means.
47. • Halzoun : worm settles in the pharynx.
• Occurs when an individual consumes infected raw liver
The young adult worms then attach themselves to the
pharyngeal mucosa causes considerable pain, edema,
and bleeding that can interfere with respiration.
• The adults can live in the biliary ducts, causing symptoms
for up to 10 years.
• Ectopic Infection: Ectopic infections through normal
transmission are infrequent but can occur in the peritoneal
cavity, intestinal wall, lungs, subcutaneous tissue, and very
rarely in other locations.
48. Fasciola hepatica:
although direct
diagnosis by
observation of eggs
in faecal smears it
the reference
method, indirect
diagnostic tests such
as IF may allow
diagnosis when direct
observation is
negative.
Immunodiagnosis by
indirect
mmunofluorescence.
Antigen: frozen
sections of Fasciola
hepatica.
49. epidemiology
49
• Infection begins when Metacercariae
infected aquatic vegetation is eaten or when
water containing Metacercariae is drunk.
Humans are often infected by eating
watercress. Human infections occur in parts
of Europe, northern Africa, Cuba, South
America, and other locales. It is one of the
most important disease agents of domestic
stock throughout the world and shows
promise of remaining so for years to come.
50. Treatment
• Bithional
• Highly Effective
• Large Dose
• High Cost
• LongTreatment Period
• Triclabendazole
• Easier to Use
• 1-2 Oral Doses in 24 hrs
• Virtually 100% Effective
• Surgery
50
51. Prevention
• The presence of a substantial reservoir - keep domestic animal
herds separate from the growing sites of aquatic. This limits the
risk of contaminating the vegetation and thus decreases both
human infection and the animal reservoir
• The presence of the intermediate host, the Lymanaea snails -
application of molluscicides to decrease the population of
Lymnaea snails.
• The opportunity for water source contamination by human and
non-human hosts
• Dietary practices that include the consumption of raw,
untreated aquatic vegetation.
