Digenetic Trematodes of Importance

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Digenetic Trematodes of Importance
We will study important digenetic trematodes
(flukes) by where they live in the definitive
host. Liver flukes Lung flukes Reproductive
System Flukes Intestinal Flukes Blood Flukes
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Liver Flukes
3 families of digenetic trematodes inhabit the
livers of mammals. Important species of medical
and veterinary importance are found in
these families.   FAMILY FASCIOLIDAE Chapter
17, p. 268-272 Large leaf-shaped flukes. Most
are parasites in livers of mammals, but 1 species
occurs in small intestine.  
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Fasciola hepatica
First trematode to be described de Brie (1379)
described this parasite as causing
____________________________________ First
trematode in which the life cycle was worked out
in 1883 - accomplished simultaneously by a
British graduate student A. P. Thomas and eminent
German parasitologist Rudolph Leuckart.
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Morphology of adult Fasciola hepatica

Large, leaf-shaped fluke, reaching a size of 30
mm long and 13 mm wide. Characteristics -
________________________ at anterior end
contains the _____________________________________
____________________________________________ -
body widens at base of oral cone to form
_______________ - identifying character
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Morphology of adult Fasciola hepatica

• Internal organs are branched
• ________________________ is branched near the
  uterus
• ________________________ is in middle of body
  near ovary
• lateral ___________________ are extensive
• _____________________ are tandem and highly
  branched
• ________________________ are highly branched
• Branching of internal organs makes them difficult
  to identify.

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Morphology of adult Fasciola hepatica

acetabulum
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Definitive hosts Distribution of Fasciola
hepatica

• Adults occur in the bile ducts of the livers of
  _____________ ____________________________________
  _______________________________________ in
  southern and western U.S.
•  - presence in sheep and cattle is of veterinary
  importance
• in Wisconsin?
• human cases? 

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Life cycle of Fasciola hepatica
1. ________________________ inhabit the
_________________ of the liver of the definitive
host. 2. ________________________ are released
into the bile, enter the duodenum, pass through
the digestive tract, and are voided in the
feces. - Eggs must be released into an aquatic
habitat and will hatch in 14 days. 3.
________________________ hatches from egg, swims
about until finding a pond snail (Lymnaea sp.),
and penetrates the snail to become a
____________ __________________________.
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Life cycle of Fasciola hepatica
4. Within the snail, the mother sporocyst
produces ____________________________ which
produce ____________________________ which
produce ________________ -Cercariae are released
from the snail 4-7 weeks after
miracidial penetration. 5. Cercariae swim
about until contacting aquatic vegetation. They
encyst on vegetation as __________________________
_.  - __________________________ is common
aquatic plant associated with human
infections.  
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Life cycle of Fasciola hepatica
6. When the definitive host ingests this aquatic
vegetation, metacercariae excyst in the
small intestine. How do the immature adults get
to the liver? ____________________________________
_____________________________________________ Adul
ts wander within the liver for some time before
reaching the bile ducts. Adults reach maturity
in 3 months.
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Pathology of Fasciola hepatica infections
Immature adults - ________________ _______________
_________________
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Pathology of Fasciola hepatica infections
Adults - presence in the bile ducts
cause 1. 2. 3. 4.
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Pathology of Fasciola hepatica infections
Problems in infected livestock -
__________________________________________________
__________________________________________________
__________________________________________________
_____ Infected livers are condemned in packing
plants.  
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Diagnosis of Fasciola hepatica infections

• ID eggs in fecal sample 
• unembryonated with distinct _____________________
  ____
• - size
• (Note A false ID can occur in a person who has
  eaten an infected cow or sheep liver. Eggs will
  be passed through the digestive tract.)

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Fasciola hepatica infections
TREATMENT - PREVENTION -
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Fascioloides magna deer liver fluke
Definitive hosts - Parasite is very large and
fleshy.
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Fascioloides magna deer liver fluke

• LIFE CYCLE is similar to that of Fasciola
  hepatica
• eggs released in deer feces into water
• miracidium hatches and penetrates snail - snail
  intermediate host in Wisconsin is Lymnaea
• sporocysts and rediae in snail produce cercariae
• free-swimming cercariae attach to aquatic plants
• metacercariae form on aquatic plant
• deer becomes infected by eating aquatic plant
  containing metacercariae
• immature adults migrate up common bile duct into
  liver tissue

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Fascioloides magna deer liver fluke
Adults occur within the __________________________
_ (not bile ducts) and cause considerable damage.
Worms become encapsulated by fibrous tissue
resulting in an extensive ________________________
___.
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Fasciolopsis buski
Common parasite of ______________________________
in the Orient SE Asia to India and the Pacific
Islands. It is estimated that over 10 million
persons are infected with this parasite.  
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Morphology of Adult Fasciolopsis buski
Size length 20-75 mm long and 20 mm wide Adult
is somewhat similar to Fasciola hepatica but
differs by (1) (2) (3)  
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Morphology of Adult Fasciolopsis buski
Other structures are distinct ___________________
_____________________________ __________________
______ ________________________ __________________
______
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Life Cycle of Fasciolopsis buski
Life Cycle is similar to that of Fasciola
hepatica except that adults inhabit the
__________________________________ (not the
liver) Dogs and pigs are common reservoir hosts.
Thus, is is a _________________
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Life Cycle of Fasciolopsis buski
Human infections are associated with eating
________________________________ _________________
_______________ Common plants are
________________________________ _________________
______________
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Pathology of Fasciolopsis buski
1. ____________________________________________
of the small intestine at the attachment site.
Causes a chronic _______________________________ 2
. Heavy infections can __________________________
_______________________ 3. ______________________
____ - parasite's waste metabolites are absorbed
and poison body cells. May cause death.
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Pathology of Fasciolopsis buski
Diagnosis _________________ ____________________
_______ These cannot be distinquished from
Fasciola hepatica (unembryonated with distinct
operculum). Treatment Drug treatment is
available. Drug of choice is ____________________
_______ Prevention -
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Family OpisthorchiidaeClonorchis sinensis -
Chap. 18, p. 287-291
Chinese liver fluke is an important parasite of
humans in the ____________________________________
______________________________ 19 million persons
infected in 1947 - more now Disease is
Clonorchiasis.
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Morphology of Clonorchis sinensis adult

• Adults are elongate, 8-25 mm long.
• Characteristic feature _____________________
  
• _____________________ at the posterior end.

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Morphology of Clonorchis sinensis adult
Other organs are distinct
_____________________ _____________________ _____
________________ _____________________ ___________
__________ _____________________ ________________
_____
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Life Cycle
1. Adult Clonorchis inhabits the
_______________________.   2. Adult releases up
to 4,000 eggs/day. Eggs are released into the
_______________? _____________________?
_____________________ 3. Egg is released into
an aquatic habitat where _________________________
_______________________(first intermediate host)
- this snail does not occur in North America  
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Life Cycle
4. Within the snail, the miracidium hatches into
a mother sporocyst ? mother rediae ?
cercariae. 5. Free-swimming cercariae attach to
_________________ (2nd intermediate host), burrow
into the muscle, and become ______________________
__
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Life Cycle
6. Human becomes infected by
__________________________________________________
______________________________________________
7. Metacercariae excyst in the human
duodenum. Immature adults migrate via
________________________ ________________________
Adults are mature in 1 month.

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Epidemiology
Life cycle is initiated by _______________________
_________________ ________________________________
______especially fish ponds where both snails and
carp are present. Privys are often built over
the fish pond.
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Epidemiology
In the Orient, fish is the main source of
protein. - raw fish is
considered a delicacy (sushi, sashimi)
- poor people cannot afford fuel to
cook fish
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Epidemiology
Metacercariae in carp can withstand pickling,
salting, smoking, and drying.   Cases of
clonorchiasis in the U.S.?   Reservoir hosts?

Carp second intermediate hosts
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Pathology
1. Hyperplasia of the _________________________ca
uses extreme thickening of the bile duct.  2.
Bile ducts become surrounded by
_________________________ resulting in pipestem
fibrosis.
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Pathology

• Bile duct may perforate and eggs can get into the
  liver parenchyma where they are surrounded by
  scar tissue resulting in ________________________
• 4. Infection may also stimulate
  ________________________
•  

White areas show cirrhosis in infected liver
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Diagnosis and Treatment

• DIAGNOSIS
• these are small with operculum at constricted
  end
• well measure them in lab to find out size!
• TREATMENT -

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Why is Clonorchis not in the U.S.?
1. 2.  
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Family DicrocoelidaeDicrocoelium dendriticum -
p. 277-279
Adults of the lancet fluke are parasitic in the
bile ducts of some 50 different species of
mammals This is _________________________________
______ Common definitive hosts are
__________________________ _______________________
___________________________. Human cases?
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Morphology of Dicrocoelium dendriticum adult
Adults are small, 6-10 mm in length. Characteristi
c feature is the _________________________________
_____________________ - testes are lobed and
tandem - posterior to the testes is
_________________________ Posterior portion of
body consists of an ___________________________

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Life Cycle of Dicrocoelium dendriticum
1. Adults occur in the _________________________
_____________________and release eggs in the bile
and eggs are deposited __________________ in the
definitive host's feces. 2. Fecal material is
fed on by a _______________________ (1st
intermediate host) that ingests the eggs.
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Life Cycle of Dicrocoelium dendriticum
3. Eggs hatch inside the snail releasing the
_________________________. These become mother
sporocysts which produce daughter sporocysts
which produce _________________________. (no
redia stage) 4. Cercariae are released from the
snail in thick mucus trails called
_________________________ formed as the snail
crawls along.
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Life Cycle of Dicrocoelium dendriticum
5. Slime balls are eaten by an
_____________________ - 2nd intermediate host. -
Most metacercariae occur in the ant's body cavity
but a few metacercariae encyst in the
_________________________  - These metacercariae
cause an _______________________
_________________________ causing the ants to
climb to the top of plants where they are easily
accessible to grazing mammals.
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Life Cycle of Dicrocoelium dendriticum
6. Grazing mammal ingests ant, metacercariae
excyst in duodenum, and worms migrate up common
bile duct into the liver.
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Differences in life cycle compared to other
trematodes
1. Life cycle occurs ______________________ 2.
Parasite causes a ______________________ of the
ant second intermediate host to increase the
chances that the life cycle will be completed
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Pathology of Dicrocoelium dendriticum infections
Pathology is similar to that of other liver
flukes involving 1. 2. Pathology of
Dicrocoelium is generally not as severe as that
caused by other liver flukes. Drug
treatment is available.
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Why are human infections with Dicrocoelium
rare? Movie from The Body Snatchers on
parasites changing behavior of intermediate
hosts